diff --git a/Sources/SWBApplePlatform/CoreMLCompiler.swift b/Sources/SWBApplePlatform/CoreMLCompiler.swift
index 17225c0a..1fd193d2 100644
--- a/Sources/SWBApplePlatform/CoreMLCompiler.swift
+++ b/Sources/SWBApplePlatform/CoreMLCompiler.swift
@@ -48,6 +48,10 @@ fileprivate struct CoreMLTaskPayload: TaskPayload, Encodable {
 
 /// The indexing info for a CoreML file.  This will be sent to the client in a property list format described below.
 fileprivate enum CoreMLIndexingInfo: Serializable, SourceFileIndexingInfo, Encodable {
+    public var compilerArguments: [String]? { nil }
+    public var indexOutputFile: String? { nil }
+    public var language: IndexingInfoLanguage? { nil }
+
     /// Setting up the code generation task did not generate an error.  It might have been disabled, which is treated as success.
     case success(generatedFilePaths: [Path]?, languageToGenerate: String, notice: String?)
     /// Setting up the code generation task failed, and we use the index to propagate an error back to Xcode.
diff --git a/Sources/SWBApplePlatform/IntentsCompiler.swift b/Sources/SWBApplePlatform/IntentsCompiler.swift
index 6d879dd1..ccffd2ff 100644
--- a/Sources/SWBApplePlatform/IntentsCompiler.swift
+++ b/Sources/SWBApplePlatform/IntentsCompiler.swift
@@ -43,6 +43,10 @@ fileprivate struct IntentsTaskPayload: TaskPayload, Encodable {
 
 /// The indexing info for an Intents file.  This will be sent to the client in a property list format described below.
 fileprivate enum IntentsIndexingInfo: Serializable, SourceFileIndexingInfo, Encodable {
+    public var compilerArguments: [String]? { nil }
+    public var indexOutputFile: String? { nil }
+    public var language: IndexingInfoLanguage? { nil }
+
     /// Setting up the code generation task did not generate an error.  It might have been disabled, which is treated as success.
     case success(generatedFilePaths: [Path])
     /// Setting up the code generation task failed, and we use the index to propagate an error back to Xcode.
diff --git a/Sources/SWBApplePlatform/MetalCompiler.swift b/Sources/SWBApplePlatform/MetalCompiler.swift
index 9830085d..133ff839 100644
--- a/Sources/SWBApplePlatform/MetalCompiler.swift
+++ b/Sources/SWBApplePlatform/MetalCompiler.swift
@@ -20,6 +20,9 @@ struct MetalSourceFileIndexingInfo: SourceFileIndexingInfo {
     let commandLine: [ByteString]
     let builtProductsDir: Path
     let toolchains: [String]
+    var compilerArguments: [String]? { commandLine.map { $0.asString } }
+    var indexOutputFile: String? { outputFile.str }
+    public var language: IndexingInfoLanguage? { .metal }
 
     init(outputFile: Path, commandLine: [ByteString], builtProductsDir: Path, toolchains: [String]) {
         self.outputFile = outputFile
@@ -49,7 +52,7 @@ struct MetalSourceFileIndexingInfo: SourceFileIndexingInfo {
 
 extension OutputPathIndexingInfo {
     fileprivate init(task: any ExecutableTask, payload: MetalIndexingPayload) {
-        self.init(outputFile: Path(task.commandLine[payload.outputFileIndex].asString))
+        self.init(outputFile: Path(task.commandLine[payload.outputFileIndex].asString), language: .metal)
     }
 }
 
diff --git a/Sources/SWBBuildService/BuildDescriptionMessages.swift b/Sources/SWBBuildService/BuildDescriptionMessages.swift
new file mode 100644
index 00000000..e6c4a3e5
--- /dev/null
+++ b/Sources/SWBBuildService/BuildDescriptionMessages.swift
@@ -0,0 +1,218 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SWBBuildSystem
+import SWBCore
+import SWBProtocol
+import SWBServiceCore
+import SWBTaskConstruction
+import SWBTaskExecution
+import SWBUtil
+
+// MARK: - Retrieve build description
+
+/// Message that contains enough information to load a build description
+private protocol BuildDescriptionMessage: SessionMessage {
+    /// The ID of the build description from which to load the configured targets
+    var buildDescriptionID: BuildDescriptionID { get }
+
+    /// The build request that was used to generate the build description with the given ID.
+    var request: BuildRequestMessagePayload { get }
+}
+
+extension BuildDescriptionConfiguredTargetsRequest: BuildDescriptionMessage {}
+extension BuildDescriptionConfiguredTargetSourcesRequest: BuildDescriptionMessage {}
+extension IndexBuildSettingsRequest: BuildDescriptionMessage {}
+
+fileprivate extension Request {
+    struct BuildDescriptionDoesNotExistError: Error {}
+
+    func buildDescription(for message: some BuildDescriptionMessage) async throws -> BuildDescription {
+        return try await buildRequestAndDescription(for: message).description
+    }
+
+    func buildRequestAndDescription(for message: some BuildDescriptionMessage) async throws -> (request: BuildRequest, description: BuildDescription) {
+        let session = try self.session(for: message)
+        guard let workspaceContext = session.workspaceContext else {
+            throw MsgParserError.missingWorkspaceContext
+        }
+        let buildRequest = try BuildRequest(from: message.request, workspace: workspaceContext.workspace)
+        let buildRequestContext = BuildRequestContext(workspaceContext: workspaceContext)
+        let clientDelegate = ClientExchangeDelegate(request: self, session: session)
+        let operation = IndexingOperation(workspace: workspaceContext.workspace)
+        let buildDescription = try await session.buildDescriptionManager.getNewOrCachedBuildDescription(
+            .cachedOnly(
+                message.buildDescriptionID,
+                request: buildRequest,
+                buildRequestContext: buildRequestContext,
+                workspaceContext: workspaceContext
+            ), clientDelegate: clientDelegate, constructionDelegate: operation
+        )?.buildDescription
+
+        guard let buildDescription else {
+            throw BuildDescriptionDoesNotExistError()
+        }
+        return (buildRequest, buildDescription)
+    }
+}
+
+// MARK: - Message handlers
+
+struct BuildDescriptionConfiguredTargetsMsg: MessageHandler {
+    /// Compute the toolchains that can handle all Swift and clang compilation tasks in the given target.
+    private func toolchainIDs(in configuredTarget: ConfiguredTarget, of buildDescription: BuildDescription) -> [String]? {
+        var toolchains: [String]?
+
+        for task in buildDescription.taskStore.tasksForTarget(configuredTarget) {
+            let targetToolchains: [String]? =
+                switch task.payload {
+                case let payload as SwiftTaskPayload: payload.indexingPayload.toolchains
+                case let payload as ClangTaskPayload: payload.indexingPayload?.toolchains
+                default: nil
+                }
+            guard let targetToolchains else {
+                continue
+            }
+            if let unwrappedToolchains = toolchains {
+                toolchains = unwrappedToolchains.filter { targetToolchains.contains($0) }
+            } else {
+                toolchains = targetToolchains
+            }
+        }
+
+        return toolchains
+    }
+
+    func handle(request: Request, message: BuildDescriptionConfiguredTargetsRequest) async throws -> BuildDescriptionConfiguredTargetsResponse {
+        let buildDescription = try await request.buildDescription(for: message)
+
+        let dependencyRelationships = Dictionary(
+            buildDescription.targetDependencies.map { (ConfiguredTarget.GUID(id: $0.target.guid), [$0]) },
+            uniquingKeysWith: { $0 + $1 }
+        )
+
+        let session = try request.session(for: message)
+
+        let targetInfos = buildDescription.allConfiguredTargets.map { configuredTarget in
+            let toolchain: Path?
+            if let toolchainID = toolchainIDs(in: configuredTarget, of: buildDescription)?.first {
+                toolchain = session.core.toolchainRegistry.lookup(toolchainID)?.path
+                if toolchain == nil {
+                    log("Unable to find path for toolchain with identifier \(toolchainID)", isError: true)
+                }
+            } else {
+                log("Unable to find toolchain for \(configuredTarget)", isError: true)
+                toolchain = nil
+            }
+
+            let dependencyRelationships = dependencyRelationships[configuredTarget.guid]
+            return BuildDescriptionConfiguredTargetsResponse.ConfiguredTargetInfo(
+                guid: ConfiguredTargetGUID(configuredTarget.guid.stringValue),
+                target: TargetGUID(rawValue: configuredTarget.target.guid),
+                name: configuredTarget.target.name,
+                dependencies: Set(dependencyRelationships?.flatMap(\.targetDependencies).map { ConfiguredTargetGUID($0.guid) } ?? []),
+                toolchain: toolchain
+            )
+        }
+        return BuildDescriptionConfiguredTargetsResponse(configuredTargets: targetInfos)
+    }
+}
+
+fileprivate extension SourceLanguage {
+    init?(_ language: IndexingInfoLanguage?) {
+        switch language {
+        case nil: return nil
+        case .c: self = .c
+        case .cpp: self = .cpp
+        case .metal: self = .metal
+        case .objectiveC: self = .objectiveC
+        case .objectiveCpp: self = .objectiveCpp
+        case .swift: self = .swift
+        }
+    }
+}
+
+struct BuildDescriptionConfiguredTargetSourcesMsg: MessageHandler {
+    private struct UnknownConfiguredTargetIDError: Error, CustomStringConvertible {
+        let configuredTarget: ConfiguredTargetGUID
+        var description: String { "Unknown configured target: \(configuredTarget)" }
+    }
+
+    typealias SourceFileInfo = BuildDescriptionConfiguredTargetSourcesResponse.SourceFileInfo
+    typealias ConfiguredTargetSourceFilesInfo = BuildDescriptionConfiguredTargetSourcesResponse.ConfiguredTargetSourceFilesInfo
+
+    func handle(request: Request, message: BuildDescriptionConfiguredTargetSourcesRequest) async throws -> BuildDescriptionConfiguredTargetSourcesResponse {
+        let buildDescription = try await request.buildDescription(for: message)
+
+        let configuredTargetsByID = Dictionary(
+            buildDescription.allConfiguredTargets.map { ($0.guid, $0) }
+        ) { lhs, rhs in
+            log("Found conflicting targets for the same ID: \(lhs.guid)", isError: true)
+            return lhs
+        }
+
+        let indexingInfoInput = TaskGenerateIndexingInfoInput(requestedSourceFile: nil, outputPathOnly: true, enableIndexBuildArena: false)
+        let sourcesItems = try message.configuredTargets.map { configuredTargetGuid in
+            guard let target = configuredTargetsByID[ConfiguredTarget.GUID(id: configuredTargetGuid.rawValue)] else {
+                throw UnknownConfiguredTargetIDError(configuredTarget: configuredTargetGuid)
+            }
+            let sourceFiles = buildDescription.taskStore.tasksForTarget(target).flatMap { task in
+                task.generateIndexingInfo(input: indexingInfoInput).compactMap { (entry) -> SourceFileInfo? in
+                    return SourceFileInfo(
+                        path: entry.path,
+                        language: SourceLanguage(entry.indexingInfo.language),
+                        outputPath: entry.indexingInfo.indexOutputFile
+                    )
+                }
+            }
+            return ConfiguredTargetSourceFilesInfo(configuredTarget: configuredTargetGuid, sourceFiles: sourceFiles)
+        }
+        return BuildDescriptionConfiguredTargetSourcesResponse(targetSourceFileInfos: sourcesItems)
+    }
+}
+
+struct IndexBuildSettingsMsg: MessageHandler {
+    private struct AmbiguousIndexingInfoError: Error, CustomStringConvertible {
+        var description: String { "Found multiple indexing informations for the same source file" }
+    }
+
+    private struct FailedToGetCompilerArgumentsError: Error {}
+
+    func handle(request: Request, message: IndexBuildSettingsRequest) async throws -> IndexBuildSettingsResponse {
+        let (buildRequest, buildDescription) = try await request.buildRequestAndDescription(for: message)
+
+        let configuredTarget = buildDescription.allConfiguredTargets.filter { $0.guid.stringValue == message.configuredTarget.rawValue }.only
+
+        let indexingInfoInput = TaskGenerateIndexingInfoInput(
+            requestedSourceFile: message.file,
+            outputPathOnly: false,
+            enableIndexBuildArena: buildRequest.enableIndexBuildArena
+        )
+        // First find all the tasks that declare the requested source file as an input file. This should narrow the list
+        // of targets down significantly.
+        let taskForSourceFile = buildDescription.taskStore.tasksForTarget(configuredTarget)
+            .filter { $0.inputPaths.contains(message.file) }
+        // Now get the indexing info for the targets that might be relevant and perform another check to ensure they
+        // actually represent the requested source file.
+        let indexingInfos =
+            taskForSourceFile
+            .flatMap { $0.generateIndexingInfo(input: indexingInfoInput) }
+            .filter({ $0.path == message.file })
+        guard let indexingInfo = indexingInfos.only else {
+            throw AmbiguousIndexingInfoError()
+        }
+        guard let compilerArguments = indexingInfo.indexingInfo.compilerArguments else {
+            throw FailedToGetCompilerArgumentsError()
+        }
+        return IndexBuildSettingsResponse(compilerArguments: compilerArguments)
+    }
+}
diff --git a/Sources/SWBBuildService/CMakeLists.txt b/Sources/SWBBuildService/CMakeLists.txt
index ac623f70..43b9ac05 100644
--- a/Sources/SWBBuildService/CMakeLists.txt
+++ b/Sources/SWBBuildService/CMakeLists.txt
@@ -10,6 +10,7 @@ See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 
 add_library(SWBBuildService
   BuildDependencyInfo.swift
+  BuildDescriptionMessages.swift
   BuildOperationMessages.swift
   BuildService.swift
   BuildServiceEntryPoint.swift
diff --git a/Sources/SWBBuildService/Messages.swift b/Sources/SWBBuildService/Messages.swift
index ded6b880..ab5b43b8 100644
--- a/Sources/SWBBuildService/Messages.swift
+++ b/Sources/SWBBuildService/Messages.swift
@@ -1614,6 +1614,10 @@ package struct ServiceMessageHandlers: ServiceExtension {
         service.registerMessageHandler(ComputeDependencyGraphMsg.self)
         service.registerMessageHandler(DumpBuildDependencyInfoMsg.self)
         
+        service.registerMessageHandler(BuildDescriptionConfiguredTargetsMsg.self)
+        service.registerMessageHandler(BuildDescriptionConfiguredTargetSourcesMsg.self)
+        service.registerMessageHandler(IndexBuildSettingsMsg.self)
+
         service.registerMessageHandler(MacroEvaluationMsg.self)
         service.registerMessageHandler(AllExportedMacrosAndValuesMsg.self)
         service.registerMessageHandler(BuildSettingsEditorInfoMsg.self)
diff --git a/Sources/SWBCore/ConfiguredTarget.swift b/Sources/SWBCore/ConfiguredTarget.swift
index 4f93f80e..5ab5c0c5 100644
--- a/Sources/SWBCore/ConfiguredTarget.swift
+++ b/Sources/SWBCore/ConfiguredTarget.swift
@@ -82,7 +82,7 @@ public final class ConfiguredTarget: Hashable, CustomStringConvertible, Serializ
     public struct GUID: Hashable, Sendable, Comparable, CustomStringConvertible {
         public let stringValue: String
 
-        fileprivate init(id: String) {
+        public init(id: String) {
             self.stringValue = id
         }
 
diff --git a/Sources/SWBCore/SpecImplementations/Tools/CCompiler.swift b/Sources/SWBCore/SpecImplementations/Tools/CCompiler.swift
index 279b0b3b..26e43bb9 100644
--- a/Sources/SWBCore/SpecImplementations/Tools/CCompiler.swift
+++ b/Sources/SWBCore/SpecImplementations/Tools/CCompiler.swift
@@ -93,7 +93,7 @@ public struct ClangPrefixInfo: Serializable, Hashable, Encodable, Sendable {
 }
 
 /// The minimal data we need to serialize to reconstruct `ClangSourceFileIndexingInfo` from `generateIndexingInfo`
-fileprivate struct ClangIndexingPayload: Serializable, Encodable, Sendable {
+public struct ClangIndexingPayload: Serializable, Encodable, Sendable {
     let sourceFileIndex: Int
     let outputFileIndex: Int
     let sourceLanguageIndex: Int
@@ -101,7 +101,7 @@ fileprivate struct ClangIndexingPayload: Serializable, Encodable, Sendable {
     let assetSymbolIndexPath: Path
     let workingDir: Path
     let prefixInfo: ClangPrefixInfo?
-    let toolchains: [String]
+    public let toolchains: [String]
     let responseFileAttachmentPaths: [Path: Path]
 
     init(sourceFileIndex: Int,
@@ -128,7 +128,7 @@ fileprivate struct ClangIndexingPayload: Serializable, Encodable, Sendable {
         return Path(task.commandLine[self.sourceFileIndex].asString)
     }
 
-    func serialize<T: Serializer>(to serializer: T) {
+    public func serialize<T: Serializer>(to serializer: T) {
         serializer.serializeAggregate(9) {
             serializer.serialize(sourceFileIndex)
             serializer.serialize(outputFileIndex)
@@ -142,7 +142,7 @@ fileprivate struct ClangIndexingPayload: Serializable, Encodable, Sendable {
         }
     }
 
-    init(from deserializer: any Deserializer) throws {
+    public init(from deserializer: any Deserializer) throws {
         try deserializer.beginAggregate(9)
         self.sourceFileIndex = try deserializer.deserialize()
         self.outputFileIndex = try deserializer.deserialize()
@@ -165,6 +165,19 @@ public struct ClangSourceFileIndexingInfo: SourceFileIndexingInfo {
     let assetSymbolIndexPath: Path
     let prefixInfo: ClangPrefixInfo?
     let toolchains: [String]
+    public var compilerArguments: [String]? {
+        var result = commandLine.map { $0.asString }
+        // commandLine does not contain the `-index-unit-output-path` but we want to return it from the
+        // `IndexBuildSettingsRequest`, so add it.
+        if !result.contains(where: { $0 == "-o" || $0 == "-index-unit-output-path" }), let indexOutputFile {
+            result += ["-index-unit-output-path", indexOutputFile]
+        }
+        return result
+    }
+    public var indexOutputFile: String? { outputFile.str }
+    public var language: IndexingInfoLanguage? {
+        return IndexingInfoLanguage(compilerArgumentLanguage: sourceLanguage)
+    }
 
     init(outputFile: Path, sourceLanguage: ByteString, commandLine: [ByteString], builtProductsDir: Path, assetSymbolIndexPath: Path, prefixInfo: ClangPrefixInfo?, toolchains: [String]) {
         self.outputFile = outputFile
@@ -280,6 +293,7 @@ public struct ClangSourceFileIndexingInfo: SourceFileIndexingInfo {
 extension OutputPathIndexingInfo {
     fileprivate init(task: any ExecutableTask, payload: ClangIndexingPayload) {
         self.outputFile = Path(task.commandLine[payload.outputFileIndex].asString)
+        self.language = IndexingInfoLanguage(compilerArgumentLanguage: task.commandLine[payload.sourceLanguageIndex].asByteString)
     }
 }
 
@@ -422,7 +436,7 @@ public struct ClangTaskPayload: ClangModuleVerifierPayloadType, DependencyInfoEd
     public let serializedDiagnosticsPath: Path?
 
     /// Additional information used to answer indexing queries.  Not all clang tasks will need to provide indexing info (for example, precompilation tasks don't).
-    fileprivate let indexingPayload: ClangIndexingPayload?
+    public let indexingPayload: ClangIndexingPayload?
 
     /// Additional information used by explicit modules support.
     public let explicitModulesPayload: ClangExplicitModulesPayload?
@@ -2120,3 +2134,15 @@ public final class ClangModuleVerifierSpec: ClangCompilerSpec, SpecImplementatio
 private func ==(lhs: ClangCompilerSpec.DataCache.ConstantFlagsKey, rhs: ClangCompilerSpec.DataCache.ConstantFlagsKey) -> Bool {
     return ObjectIdentifier(lhs.scope) == ObjectIdentifier(rhs.scope) && lhs.inputFileType == rhs.inputFileType
 }
+
+private extension IndexingInfoLanguage {
+    init?(compilerArgumentLanguage: ByteString) {
+        switch compilerArgumentLanguage {
+        case "c": self = .c
+        case "c++": self = .cpp
+        case "objective-c": self = .objectiveC
+        case "objective-c++": self = .objectiveCpp
+        default: return nil
+        }
+    }
+}
diff --git a/Sources/SWBCore/SpecImplementations/Tools/SwiftCompiler.swift b/Sources/SWBCore/SpecImplementations/Tools/SwiftCompiler.swift
index 44b99a76..9effd838 100644
--- a/Sources/SWBCore/SpecImplementations/Tools/SwiftCompiler.swift
+++ b/Sources/SWBCore/SpecImplementations/Tools/SwiftCompiler.swift
@@ -95,7 +95,18 @@ public struct SwiftSourceFileIndexingInfo: SourceFileIndexingInfo {
     let builtProductsDir: Path
     let assetSymbolIndexPath: Path
     let toolchains: [String]
-    let outputFile: Path
+    public let outputFile: Path
+    public var compilerArguments: [String]? {
+        var result = commandLine.map { $0.asString }
+        // commandLine does not contain the `-index-unit-output-path` but we want to return it from the
+        // `IndexBuildSettingsRequest`, so add it.
+        if !result.contains(where: { $0 == "-o" || $0 == "-index-unit-output-path" }), let indexOutputFile {
+            result += ["-index-unit-output-path", indexOutputFile]
+        }
+        return result
+     }
+    public var indexOutputFile: String? { outputFile.str }
+    public var language: IndexingInfoLanguage? { .swift }
 
     public init(task: any ExecutableTask, payload: SwiftIndexingPayload, outputFile: Path, enableIndexBuildArena: Bool, integratedDriver: Bool) {
         self.commandLine = Self.indexingCommandLine(commandLine: task.commandLine.map(\.asByteString), payload: payload, enableIndexBuildArena: enableIndexBuildArena, integratedDriver: integratedDriver)
@@ -3267,7 +3278,7 @@ public final class SwiftCompilerSpec : CompilerSpec, SpecIdentifierType, SwiftDi
                                                                    objectFileDir: payload.indexingPayload.objectFileDir, fileExtension: ".o")
             let indexingInfo: any SourceFileIndexingInfo
             if input.outputPathOnly {
-                indexingInfo = OutputPathIndexingInfo(outputFile: outputFile)
+                indexingInfo = OutputPathIndexingInfo(outputFile: outputFile, language: .swift)
             } else {
                 indexingInfo = SwiftSourceFileIndexingInfo(task: task, payload: payload.indexingPayload, outputFile: outputFile, enableIndexBuildArena: input.enableIndexBuildArena, integratedDriver: payload.driverPayload != nil)
             }
diff --git a/Sources/SWBCore/TaskGeneration.swift b/Sources/SWBCore/TaskGeneration.swift
index 7ef96613..53db7891 100644
--- a/Sources/SWBCore/TaskGeneration.swift
+++ b/Sources/SWBCore/TaskGeneration.swift
@@ -1020,18 +1020,46 @@ extension DependencyDataStyle: Serializable {
 public protocol TaskPayload: Serializable, Sendable {
 }
 
+public enum IndexingInfoLanguage {
+    case c
+    case cpp
+    case metal
+    case objectiveC
+    case objectiveCpp
+    case swift
+}
+
 /// Defines the indexing information to be sent back to the client for a particular source file.
 ///
 /// This protocol includes `PropertyListItemConvertible` to describe how the info is packaged up to send back to the client.  Someday we hope to transition this to sending the info in a strongly typed format.
 public protocol SourceFileIndexingInfo: PropertyListItemConvertible {
+    /// The compiler arguments that should be used to index this source file.
+    ///
+    /// `nil` if this indexing info does not supply compiler arguments to index a source file.
+    var compilerArguments: [String]? { get }
+
+    /// The output path that is used for indexing, ie. the value of the `-index-unit-output-path` or `-o` option in
+    /// the source file's build settings.
+    ///
+    /// This is a `String` and not a `Path` because th index output path may be a fake path that is relative to the
+    /// build directory and has no relation to actual files on disks.
+    ///
+    /// `nil` if this indexing info does not produce an output file.
+    var indexOutputFile: String? { get }
+
+    var language: IndexingInfoLanguage? { get }
 }
 
 /// The `SourceFileIndexingInfo` info returned when only output paths are requested.
 public struct OutputPathIndexingInfo: SourceFileIndexingInfo {
     public let outputFile: Path
+    public var compilerArguments: [String]? { nil }
+    public var indexOutputFile: String? { outputFile.str }
+    public let language: IndexingInfoLanguage?
 
-    public init(outputFile: Path) {
+    public init(outputFile: Path, language: IndexingInfoLanguage?) {
         self.outputFile = outputFile
+        self.language = language
     }
 
     /// The indexing info is packaged and sent to the client in a property list format.
diff --git a/Sources/SWBProtocol/BuildAction.swift b/Sources/SWBProtocol/BuildAction.swift
index 11a37542..443bc4f0 100644
--- a/Sources/SWBProtocol/BuildAction.swift
+++ b/Sources/SWBProtocol/BuildAction.swift
@@ -86,7 +86,7 @@ public enum BuildAction: String, Serializable, Codable, CaseIterable, Comparable
 }
 
 /// Opaque token used to uniquely identify a build description.
-public struct BuildDescriptionID: Hashable, Sendable {
+public struct BuildDescriptionID: Hashable, Sendable, SerializableCodable {
     public let rawValue: String
 
     public init(_ value: String) {
diff --git a/Sources/SWBProtocol/BuildDescriptionMessages.swift b/Sources/SWBProtocol/BuildDescriptionMessages.swift
new file mode 100644
index 00000000..36cace79
--- /dev/null
+++ b/Sources/SWBProtocol/BuildDescriptionMessages.swift
@@ -0,0 +1,227 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+public import SWBUtil
+
+// MARK: Support types
+
+public struct ConfiguredTargetGUID: Hashable, Sendable, Codable {
+    public var rawValue: String
+
+    public init(_ rawValue: String) {
+        self.rawValue = rawValue
+    }
+}
+
+/// The language of a source file
+public enum SourceLanguage: Hashable, Sendable, Codable {
+    case c
+    case cpp
+    case metal
+    case objectiveC
+    case objectiveCpp
+    case swift
+}
+
+// MARK: Requests
+
+/// Get the configured targets inside a pre-generated build description, their dependencies and some supplementary
+/// information about the targets.
+public struct BuildDescriptionConfiguredTargetsRequest: SessionMessage, RequestMessage, SerializableCodable, Equatable {
+    public typealias ResponseMessage = BuildDescriptionConfiguredTargetsResponse
+
+    public static let name = "BUILD_DESCRIPTION_CONFIGURED_TARGETS_REQUEST"
+
+    public let sessionHandle: String
+
+    /// The ID of the build description from which to load the configured targets
+    public let buildDescriptionID: BuildDescriptionID
+
+    /// The build request that was used to generate the build description with the given ID.
+    public let request: BuildRequestMessagePayload
+
+    public init(sessionHandle: String, buildDescriptionID: BuildDescriptionID, request: BuildRequestMessagePayload) {
+        self.sessionHandle = sessionHandle
+        self.buildDescriptionID = buildDescriptionID
+        self.request = request
+    }
+}
+
+public struct BuildDescriptionConfiguredTargetsResponse: Message, SerializableCodable, Equatable {
+    public static let name = "BUILD_DESCRIPTION_CONFIGURED_TARGETS_RESPONSE"
+
+    public struct ConfiguredTargetInfo: SerializableCodable, Equatable, Sendable {
+        /// The GUID of this configured target
+        public let guid: ConfiguredTargetGUID
+
+        /// The GUID of the target from which this configured target was created
+        public let target: TargetGUID
+
+        /// A name of the target that may be displayed to the user
+        public let name: String
+
+        /// The configured targets that this target depends on
+        public let dependencies: Set<ConfiguredTargetGUID>
+
+        /// The path of the toolchain that should be used to build this target.
+        ///
+        /// `nil` if the toolchain for this target could not be determined due to an error.
+        public let toolchain: Path?
+
+        public init(guid: ConfiguredTargetGUID, target: TargetGUID, name: String, dependencies: Set<ConfiguredTargetGUID>, toolchain: Path?) {
+            self.guid = guid
+            self.target = target
+            self.name = name
+            self.dependencies = dependencies
+            self.toolchain = toolchain
+        }
+    }
+
+    public let configuredTargets: [ConfiguredTargetInfo]
+
+    public init(configuredTargets: [ConfiguredTargetInfo]) {
+        self.configuredTargets = configuredTargets
+    }
+}
+
+/// Get information about the source files in a list of configured targets.
+public struct BuildDescriptionConfiguredTargetSourcesRequest: SessionMessage, RequestMessage, SerializableCodable, Equatable {
+    public typealias ResponseMessage = BuildDescriptionConfiguredTargetSourcesResponse
+
+    public static let name = "BUILD_DESCRIPTION_CONFIGURED_TARGET_SOURCES_REQUEST"
+
+    public var sessionHandle: String
+
+    /// The ID of the build description in which the configured targets reside
+    public let buildDescriptionID: BuildDescriptionID
+
+    /// The build request that was used to generate the build description with the given ID.
+    public let request: BuildRequestMessagePayload
+
+    /// The configured targets for which to load source file information
+    public let configuredTargets: [ConfiguredTargetGUID]
+
+    public init(sessionHandle: String, buildDescriptionID: BuildDescriptionID, request: BuildRequestMessagePayload, configuredTargets: [ConfiguredTargetGUID]) {
+        self.sessionHandle = sessionHandle
+        self.buildDescriptionID = buildDescriptionID
+        self.request = request
+        self.configuredTargets = configuredTargets
+    }
+}
+
+public struct BuildDescriptionConfiguredTargetSourcesResponse: Message, SerializableCodable, Equatable {
+    public static let name = "BUILD_DESCRIPTION_CONFIGURED_TARGET_SOURCES_RESPONSE"
+
+    public struct SourceFileInfo: SerializableCodable, Equatable, Sendable {
+        /// The path of the source file on disk
+        public let path: Path
+
+        /// The language of the source file.
+        ///
+        /// `nil` if the language could not be determined due to an error.
+        public let language: SourceLanguage?
+
+        /// The output path that is used for indexing, ie. the value of the `-index-unit-output-path` or `-o` option in
+        /// the source file's build settings.
+        ///
+        /// This is a `String` and not a `Path` because th index output path may be a fake path that is relative to the
+        /// build directory and has no relation to actual files on disks.
+        ///
+        /// May be `nil` if the output path could not be determined due to an error.
+        public let indexOutputPath: String?
+
+        public init(path: Path, language: SourceLanguage?, outputPath: String?) {
+            self.path = path
+            self.language = language
+            self.indexOutputPath = outputPath
+        }
+    }
+
+    public struct ConfiguredTargetSourceFilesInfo: SerializableCodable, Equatable, Sendable {
+        /// The configured target to which this info belongs
+        public let configuredTarget: ConfiguredTargetGUID
+
+        /// Information about the source files in this source file
+        public let sourceFiles: [SourceFileInfo]
+
+        public init(configuredTarget: ConfiguredTargetGUID, sourceFiles: [SourceFileInfo]) {
+            self.configuredTarget = configuredTarget
+            self.sourceFiles = sourceFiles
+        }
+    }
+
+    /// For each requested configured target, the response contains one entry in this array
+    public let targetSourceFileInfos: [ConfiguredTargetSourceFilesInfo]
+
+    public init(targetSourceFileInfos: [ConfiguredTargetSourceFilesInfo]) {
+        self.targetSourceFileInfos = targetSourceFileInfos
+    }
+}
+
+/// Load the build settings that should be used to index a source file in a given configured target
+public struct IndexBuildSettingsRequest: SessionMessage, RequestMessage, SerializableCodable, Equatable {
+    public typealias ResponseMessage = IndexBuildSettingsResponse
+
+    public static let name = "INDEX_BUILD_SETTINGS_REQUEST"
+
+    public var sessionHandle: String
+
+    /// The ID of the build description in which the configured targets reside
+    public let buildDescriptionID: BuildDescriptionID
+
+    /// The build request that was used to generate the build description with the given ID.
+    public let request: BuildRequestMessagePayload
+
+    /// The configured target in whose context the build settings of the source file should be loaded
+    public let configuredTarget: ConfiguredTargetGUID
+
+    /// The path of the source file for which the build settings should be loaded
+    public let file: Path
+
+    public init(
+        sessionHandle: String,
+        buildDescriptionID: BuildDescriptionID,
+        request: BuildRequestMessagePayload,
+        configuredTarget: ConfiguredTargetGUID,
+        file: Path
+    ) {
+        self.sessionHandle = sessionHandle
+        self.buildDescriptionID = buildDescriptionID
+        self.request = request
+        self.configuredTarget = configuredTarget
+        self.file = file
+    }
+}
+
+public struct IndexBuildSettingsResponse: Message, SerializableCodable, Equatable {
+    public static let name = "INDEX_BUILD_SETTINGS_RESPONSE"
+
+    /// The arguments that should be passed to the compiler to index the source file.
+    ///
+    /// This does not include the path to the compiler executable itself.
+    public let compilerArguments: [String]
+
+    public init(compilerArguments: [String]) {
+        self.compilerArguments = compilerArguments
+    }
+}
+
+// MARK: Registering messages
+
+let buildDescriptionMessages: [any Message.Type] = [
+    BuildDescriptionConfiguredTargetsRequest.self,
+    BuildDescriptionConfiguredTargetsResponse.self,
+    BuildDescriptionConfiguredTargetSourcesRequest.self,
+    BuildDescriptionConfiguredTargetSourcesResponse.self,
+    IndexBuildSettingsRequest.self,
+    IndexBuildSettingsResponse.self,
+]
diff --git a/Sources/SWBProtocol/CMakeLists.txt b/Sources/SWBProtocol/CMakeLists.txt
index 9208d4b2..8fdbe81d 100644
--- a/Sources/SWBProtocol/CMakeLists.txt
+++ b/Sources/SWBProtocol/CMakeLists.txt
@@ -11,6 +11,7 @@ See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 add_library(SWBProtocol
   AsyncSequence.swift
   BuildAction.swift
+  BuildDescriptionMessages.swift
   BuildOperationMessages.swift
   BuildSettingsInfoMessageTypes.swift
   ClientExchangeMessages.swift
diff --git a/Sources/SWBProtocol/Message.swift b/Sources/SWBProtocol/Message.swift
index c32a01ad..dce784c0 100644
--- a/Sources/SWBProtocol/Message.swift
+++ b/Sources/SWBProtocol/Message.swift
@@ -1218,6 +1218,7 @@ public struct IPCMessage: Serializable, Sendable {
       + localizationMessageTypes
       + dependencyClosureMessageTypes
       + dependencyGraphMessageTypes
+      + buildDescriptionMessages
 
     /// Reverse name mapping.
     static let messageNameToID: [String: any Message.Type] = {
diff --git a/Sources/SwiftBuild/CMakeLists.txt b/Sources/SwiftBuild/CMakeLists.txt
index 45970977..9a1bbea2 100644
--- a/Sources/SwiftBuild/CMakeLists.txt
+++ b/Sources/SwiftBuild/CMakeLists.txt
@@ -31,6 +31,7 @@ add_library(SwiftBuild
   ProjectModel/TargetDependency.swift
   ProjectModel/Targets.swift
   SWBBuildAction.swift
+  SWBBuildDescriptionID.swift
   SWBBuildOperation.swift
   SWBBuildOperationBacktraceFrame.swift
   SWBBuildParameters.swift
@@ -41,6 +42,9 @@ add_library(SwiftBuild
   SWBBuildServiceSession.swift
   SWBChannel.swift
   SWBClientExchangeSupport.swift
+  SWBConfiguredTargetGUID.swift
+  SWBConfiguredTargetInfo.swift
+  SWBConfiguredTargetSourceFilesInfo.swift
   SWBDocumentationSupport.swift
   SWBIndexingSupport.swift
   SWBLocalizationSupport.swift
@@ -49,6 +53,7 @@ add_library(SwiftBuild
   SWBProductPlannerSupport.swift
   SWBPropertyList.swift
   SWBProvisioningTaskInputs.swift
+  SWBSourceLanguage.swift
   SWBSystemInfo.swift
   SWBTargetGUID.swift
   SWBTerminal.swift
diff --git a/Sources/SwiftBuild/ConsoleCommands/SWBServiceConsoleBuildCommandProtocol.swift b/Sources/SwiftBuild/ConsoleCommands/SWBServiceConsoleBuildCommandProtocol.swift
index 28283569..46f97977 100644
--- a/Sources/SwiftBuild/ConsoleCommands/SWBServiceConsoleBuildCommandProtocol.swift
+++ b/Sources/SwiftBuild/ConsoleCommands/SWBServiceConsoleBuildCommandProtocol.swift
@@ -925,6 +925,17 @@ public struct AbsolutePath: Hashable, Equatable, Sendable {
         self.pathString = path
     }
 
+    init(_ path: Path) {
+        self.pathString = path.str
+    }
+
+    init?(_ path: Path?) {
+        guard let path else {
+            return nil
+        }
+        self.init(path)
+    }
+
     public static let root = try! AbsolutePath(validating: Path.root.str)
 }
 
diff --git a/Sources/SwiftBuild/SWBBuildDescriptionID.swift b/Sources/SwiftBuild/SWBBuildDescriptionID.swift
new file mode 100644
index 00000000..33b766ca
--- /dev/null
+++ b/Sources/SwiftBuild/SWBBuildDescriptionID.swift
@@ -0,0 +1,32 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SWBProtocol
+
+/// Opaque token used to uniquely identify a build description.
+public struct SWBBuildDescriptionID: Hashable, Sendable {
+    public let rawValue: String
+
+    public init(_ value: String) {
+        self.rawValue = value
+    }
+
+    init(_ buildDescriptionID: BuildDescriptionID) {
+        self.rawValue = buildDescriptionID.rawValue
+    }
+}
+
+extension BuildDescriptionID {
+    init(_ buildDescriptionID: SWBBuildDescriptionID) {
+        self.init(buildDescriptionID.rawValue)
+    }
+}
diff --git a/Sources/SwiftBuild/SWBBuildServiceSession.swift b/Sources/SwiftBuild/SWBBuildServiceSession.swift
index 07b29c65..c96d6c7e 100644
--- a/Sources/SwiftBuild/SWBBuildServiceSession.swift
+++ b/Sources/SwiftBuild/SWBBuildServiceSession.swift
@@ -388,6 +388,35 @@ public final class SWBBuildServiceSession: Sendable {
         return result
     }
 
+    public func configuredTargets(buildDescription: SWBBuildDescriptionID, buildRequest: SWBBuildRequest) async throws -> [SWBConfiguredTargetInfo] {
+        let response = try await service.send(request: BuildDescriptionConfiguredTargetsRequest(sessionHandle: uid, buildDescriptionID: BuildDescriptionID(buildDescription), request: buildRequest.messagePayloadRepresentation))
+        return response.configuredTargets.map { SWBConfiguredTargetInfo($0) }
+    }
+
+    public func sources(of configuredTargets: [SWBConfiguredTargetGUID], buildDescription: SWBBuildDescriptionID, buildRequest: SWBBuildRequest) async throws -> [SWBConfiguredTargetSourceFilesInfo] {
+        let response = try await service.send(
+            request: BuildDescriptionConfiguredTargetSourcesRequest(
+                sessionHandle: uid,
+                buildDescriptionID: BuildDescriptionID(buildDescription),
+                request: buildRequest.messagePayloadRepresentation,
+                configuredTargets: configuredTargets.map { ConfiguredTargetGUID($0) }
+            )
+        )
+        return response.targetSourceFileInfos.map { SWBConfiguredTargetSourceFilesInfo($0) }
+    }
+
+    public func indexCompilerArguments(of file: AbsolutePath, in configuredTarget: SWBConfiguredTargetGUID, buildDescription: SWBBuildDescriptionID, buildRequest: SWBBuildRequest) async throws -> [String] {
+        let buildSettings = try await service.send(
+            request: IndexBuildSettingsRequest(
+                sessionHandle: uid,
+                buildDescriptionID: BuildDescriptionID(buildDescription),
+                request: buildRequest.messagePayloadRepresentation,
+                configuredTarget: ConfiguredTargetGUID(configuredTarget),
+                file: Path(file.pathString)
+            )
+        )
+        return buildSettings.compilerArguments
+    }
 
     // MARK: Macro evaluation
 
diff --git a/Sources/SwiftBuild/SWBConfiguredTargetGUID.swift b/Sources/SwiftBuild/SWBConfiguredTargetGUID.swift
new file mode 100644
index 00000000..4b193169
--- /dev/null
+++ b/Sources/SwiftBuild/SWBConfiguredTargetGUID.swift
@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SWBProtocol
+
+public struct SWBConfiguredTargetGUID: RawRepresentable, Hashable, Sendable {
+    public var rawValue: String
+
+    public init(rawValue: String) {
+        self.rawValue = rawValue
+    }
+
+    init(_ guid: ConfiguredTargetGUID) {
+        self.init(rawValue: guid.rawValue)
+    }
+}
+
+extension ConfiguredTargetGUID {
+    init(_ guid: SWBConfiguredTargetGUID) {
+        self.init(guid.rawValue)
+    }
+}
diff --git a/Sources/SwiftBuild/SWBConfiguredTargetInfo.swift b/Sources/SwiftBuild/SWBConfiguredTargetInfo.swift
new file mode 100644
index 00000000..410924c1
--- /dev/null
+++ b/Sources/SwiftBuild/SWBConfiguredTargetInfo.swift
@@ -0,0 +1,50 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SWBProtocol
+
+public struct SWBConfiguredTargetInfo {
+    /// The GUID of this configured target
+    public let guid: SWBConfiguredTargetGUID
+
+    /// The GUID of the target from which this configured target was created
+    public let target: SWBTargetGUID
+
+    /// A name of the target that may be displayed to the user
+    public let name: String
+
+    /// The configured targets that this target depends on
+    public let dependencies: Set<SWBConfiguredTargetGUID>
+
+    /// The path of the toolchain that should be used to build this target.
+    ///
+    /// `nil` if the toolchain for this target could not be determined due to an error.
+    public let toolchain: AbsolutePath?
+
+    public init(guid: SWBConfiguredTargetGUID, target: SWBTargetGUID, name: String, dependencies: Set<SWBConfiguredTargetGUID>, toolchain: AbsolutePath?) {
+        self.guid = guid
+        self.target = target
+        self.name = name
+        self.dependencies = dependencies
+        self.toolchain = toolchain
+    }
+
+    init(_ configuredTargetInfo: BuildDescriptionConfiguredTargetsResponse.ConfiguredTargetInfo) {
+        self.init(
+            guid: SWBConfiguredTargetGUID(configuredTargetInfo.guid),
+            target: SWBTargetGUID(configuredTargetInfo.target),
+            name: configuredTargetInfo.name,
+            dependencies: Set(configuredTargetInfo.dependencies.map { SWBConfiguredTargetGUID($0) }),
+            toolchain: AbsolutePath(configuredTargetInfo.toolchain)
+        )
+    }
+}
diff --git a/Sources/SwiftBuild/SWBConfiguredTargetSourceFilesInfo.swift b/Sources/SwiftBuild/SWBConfiguredTargetSourceFilesInfo.swift
new file mode 100644
index 00000000..d87f5927
--- /dev/null
+++ b/Sources/SwiftBuild/SWBConfiguredTargetSourceFilesInfo.swift
@@ -0,0 +1,62 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SWBProtocol
+
+public struct SWBConfiguredTargetSourceFilesInfo: Equatable, Sendable {
+    public struct SourceFileInfo: Equatable, Sendable {
+        /// The path of the source file on disk
+        public let path: AbsolutePath
+
+        /// The language of the source file.
+        ///
+        /// `nil` if the language could not be determined due to an error.
+        public let language: SWBSourceLanguage?
+
+        /// The output path that is used for indexing, ie. the value of the `-index-unit-output-path` or `-o` option in
+        /// the source file's build settings.
+        ///
+        /// This is a `String` and not a `Path` because th index output path may be a fake path that is relative to the
+        /// build directory and has no relation to actual files on disks.
+        ///
+        /// May be `nil` if the output path could not be determined due to an error.
+        public let indexOutputPath: String?
+
+        public init(path: AbsolutePath, language: SWBSourceLanguage? = nil, indexOutputPath: String? = nil) {
+            self.path = path
+            self.language = language
+            self.indexOutputPath = indexOutputPath
+        }
+
+        init(_ sourceFileInfo: BuildDescriptionConfiguredTargetSourcesResponse.SourceFileInfo) {
+            self.path = AbsolutePath(sourceFileInfo.path)
+            self.language = SWBSourceLanguage(sourceFileInfo.language)
+            self.indexOutputPath = sourceFileInfo.indexOutputPath
+        }
+    }
+
+    /// The configured target to which this info belongs
+    public let configuredTarget: SWBConfiguredTargetGUID
+
+    /// Information about the source files in this source file
+    public let sourceFiles: [SourceFileInfo]
+
+    public init(configuredTarget: SWBConfiguredTargetGUID, sourceFiles: [SWBConfiguredTargetSourceFilesInfo.SourceFileInfo]) {
+        self.configuredTarget = configuredTarget
+        self.sourceFiles = sourceFiles
+    }
+
+    init(_ sourceFilesInfo: BuildDescriptionConfiguredTargetSourcesResponse.ConfiguredTargetSourceFilesInfo) {
+        self.configuredTarget = SWBConfiguredTargetGUID(sourceFilesInfo.configuredTarget)
+        self.sourceFiles = sourceFilesInfo.sourceFiles.map { SourceFileInfo($0) }
+    }
+}
diff --git a/Sources/SwiftBuild/SWBSourceLanguage.swift b/Sources/SwiftBuild/SWBSourceLanguage.swift
new file mode 100644
index 00000000..edf5d75f
--- /dev/null
+++ b/Sources/SwiftBuild/SWBSourceLanguage.swift
@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SWBProtocol
+
+public enum SWBSourceLanguage: Hashable, Sendable {
+    case c
+    case cpp
+    case metal
+    case objectiveC
+    case objectiveCpp
+    case swift
+
+    init?(_ language: SourceLanguage?) {
+        guard let language else {
+            return nil
+        }
+        self.init(language)
+    }
+
+    init(_ language: SourceLanguage) {
+        switch language {
+        case .c: self = .c
+        case .cpp: self = .cpp
+        case .metal: self = .metal
+        case .objectiveC: self = .objectiveC
+        case .objectiveCpp: self = .objectiveCpp
+        case .swift: self = .swift
+        }
+    }
+}
diff --git a/Sources/SwiftBuild/SWBTargetGUID.swift b/Sources/SwiftBuild/SWBTargetGUID.swift
index 922c00c4..c70f433f 100644
--- a/Sources/SwiftBuild/SWBTargetGUID.swift
+++ b/Sources/SwiftBuild/SWBTargetGUID.swift
@@ -10,10 +10,16 @@
 //
 //===----------------------------------------------------------------------===//
 
+import SWBProtocol
+
 public struct SWBTargetGUID: RawRepresentable, Hashable, Sendable {
     public var rawValue: String
 
     public init(rawValue: String) {
         self.rawValue = rawValue
     }
+
+    init(_ guid: TargetGUID) {
+        self.init(rawValue: guid.rawValue)
+    }
 }
diff --git a/Tests/SwiftBuildTests/InspectBuildDescriptionTests.swift b/Tests/SwiftBuildTests/InspectBuildDescriptionTests.swift
new file mode 100644
index 00000000..e4fde56a
--- /dev/null
+++ b/Tests/SwiftBuildTests/InspectBuildDescriptionTests.swift
@@ -0,0 +1,239 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import Testing
+import SwiftBuild
+import SwiftBuildTestSupport
+import SWBTestSupport
+@_spi(Testing) import SWBUtil
+import SWBProtocol
+import SWBCore
+
+// These tests use the old model, ie. the index build arena is disabled.
+@Suite(.requireHostOS(.macOS))
+fileprivate struct InspectBuildDescriptionTests {
+    @Test
+    func configuredTargets() async throws {
+        try await withTemporaryDirectory { (temporaryDirectory: NamedTemporaryDirectory) in
+            try await withAsyncDeferrable { deferrable in
+                let tmpDir = temporaryDirectory.path
+                let testSession = try await TestSWBSession(temporaryDirectory: temporaryDirectory)
+                await deferrable.addBlock {
+                    await #expect(throws: Never.self) {
+                        try await testSession.close()
+                    }
+                }
+
+                let frameworkTarget = TestStandardTarget(
+                    "MyFramework",
+                    type: .framework,
+                    buildPhases: [TestSourcesBuildPhase([TestBuildFile("MyFramework.swift")])],
+                )
+
+                let appTarget = TestStandardTarget(
+                    "MyApp",
+                    type: .application,
+                    buildPhases: [TestSourcesBuildPhase([TestBuildFile("MyApp.swift")])],
+                    dependencies: [TestTargetDependency("MyFramework")]
+                )
+
+                let project = TestProject(
+                    "Test",
+                    groupTree: TestGroup("Test", children: [TestFile("MyFramework.swift"), TestFile("MyApp.swift")]),
+                    targets: [frameworkTarget, appTarget]
+                )
+
+                try await testSession.sendPIF(TestWorkspace("Test", sourceRoot: tmpDir, projects: [project]))
+
+                let activeRunDestination = SWBRunDestinationInfo.macOS
+                let buildParameters = SWBBuildParameters(configuration: "Debug", activeRunDestination: activeRunDestination)
+                var request = SWBBuildRequest()
+                request.add(target: SWBConfiguredTarget(guid: appTarget.guid, parameters: buildParameters))
+
+                let buildDescriptionID = try await testSession.session.createBuildDescription(buildRequest: request)
+                let targetInfos = try await testSession.session.configuredTargets(buildDescription: buildDescriptionID, buildRequest: request)
+
+                #expect(Set(targetInfos.map(\.name)) == ["MyFramework", "MyApp"])
+                let frameworkTargetInfo = try #require(targetInfos.filter { $0.name == "MyFramework" }.only)
+                #expect(frameworkTargetInfo.dependencies == [])
+                #expect(frameworkTargetInfo.toolchain != nil)
+                let appTargetInfo = try #require(targetInfos.filter { $0.name == "MyApp" }.only)
+                #expect(appTargetInfo.dependencies == [frameworkTargetInfo.guid])
+                #expect(appTargetInfo.toolchain != nil)
+            }
+        }
+    }
+
+    @Test
+    func configuredTargetSources() async throws {
+        try await withTemporaryDirectory { (temporaryDirectory: NamedTemporaryDirectory) in
+            try await withAsyncDeferrable { deferrable in
+                let tmpDir = temporaryDirectory.path
+                let testSession = try await TestSWBSession(temporaryDirectory: temporaryDirectory)
+                await deferrable.addBlock {
+                    await #expect(throws: Never.self) {
+                        try await testSession.close()
+                    }
+                }
+
+                let appTarget = TestStandardTarget(
+                    "MyApp",
+                    type: .application,
+                    buildPhases: [TestSourcesBuildPhase([TestBuildFile("MyApp.swift")])]
+                )
+
+                let otherAppTarget = TestStandardTarget(
+                    "MyOtherApp",
+                    type: .application,
+                    buildPhases: [TestSourcesBuildPhase([TestBuildFile("MyOtherApp.swift")])]
+                )
+
+                let project = TestProject(
+                    "Test",
+                    groupTree: TestGroup("Test", children: [TestFile("MyApp.swift"), TestFile("MyOtherApp.swift")]),
+                    targets: [appTarget, otherAppTarget]
+                )
+
+                try await testSession.sendPIF(TestWorkspace("Test", sourceRoot: tmpDir, projects: [project]))
+
+                let activeRunDestination = SWBRunDestinationInfo.macOS
+                var buildParameters = SWBBuildParameters(configuration: "Debug", activeRunDestination: activeRunDestination)
+                buildParameters.overrides = SWBSettingsOverrides()
+                buildParameters.overrides.commandLine = SWBSettingsTable()
+                // Set `ONLY_ACTIVE_ARCH`, otherwise we get two entries for each Swift file, one for each architecture
+                // with a different output path.
+                buildParameters.overrides.commandLine!.set(value: "YES", for: "ONLY_ACTIVE_ARCH")
+                var request = SWBBuildRequest()
+                request.add(target: SWBConfiguredTarget(guid: appTarget.guid, parameters: buildParameters))
+                request.add(target: SWBConfiguredTarget(guid: otherAppTarget.guid, parameters: buildParameters))
+
+                let buildDescriptionID = try await testSession.session.createBuildDescription(buildRequest: request)
+                let targetInfos = try await testSession.session.configuredTargets(buildDescription: buildDescriptionID, buildRequest: request)
+                let appTargetInfo = try #require(targetInfos.filter { $0.name == "MyApp" }.only)
+                let otherAppTargetInfo = try #require(targetInfos.filter { $0.name == "MyOtherApp" }.only)
+
+                let appSources = try #require(await testSession.session.sources(of: [appTargetInfo.guid], buildDescription: buildDescriptionID, buildRequest: request).only)
+                #expect(appSources.configuredTarget == appTargetInfo.guid)
+                print(appSources.sourceFiles)
+                let myAppFile = try #require(appSources.sourceFiles.only)
+                #expect(myAppFile.path.pathString.hasSuffix("MyApp.swift"))
+                #expect(myAppFile.language == .swift)
+                #expect(myAppFile.indexOutputPath != nil)
+
+                let combinedSources = try await testSession.session.sources(
+                    of: [appTargetInfo.guid, otherAppTargetInfo.guid],
+                    buildDescription: buildDescriptionID,
+                    buildRequest: request
+                )
+                #expect(Set(combinedSources.map(\.configuredTarget)) == [appTargetInfo.guid, otherAppTargetInfo.guid])
+                #expect(Set(combinedSources.flatMap(\.sourceFiles).map { URL(filePath: $0.path.pathString).lastPathComponent }) == ["MyApp.swift", "MyOtherApp.swift"])
+
+                let emptyTargetListInfos = try await testSession.session.sources(of: [], buildDescription: buildDescriptionID, buildRequest: request)
+                #expect(emptyTargetListInfos == [])
+
+                await #expect(throws: (any Error).self) {
+                    try await testSession.session.sources(
+                        of: [SWBConfiguredTargetGUID(rawValue: "does-not-exist")],
+                        buildDescription: buildDescriptionID,
+                        buildRequest: request
+                    )
+                }
+            }
+        }
+    }
+
+    @Test
+    func indexCompilerArguments() async throws {
+        try await withTemporaryDirectory { (temporaryDirectory: NamedTemporaryDirectory) in
+            try await withAsyncDeferrable { deferrable in
+                let tmpDir = temporaryDirectory.path
+                let testSession = try await TestSWBSession(temporaryDirectory: temporaryDirectory)
+                await deferrable.addBlock {
+                    await #expect(throws: Never.self) {
+                        try await testSession.close()
+                    }
+                }
+
+                let appTarget = TestStandardTarget(
+                    "MyApp",
+                    type: .application,
+                    buildConfigurations: [TestBuildConfiguration("Debug", buildSettings: ["SWIFT_ACTIVE_COMPILATION_CONDITIONS": "MY_APP"])],
+                    buildPhases: [TestSourcesBuildPhase([TestBuildFile("MyApp.swift")])]
+                )
+
+                let otherAppTarget = TestStandardTarget(
+                    "MyOtherApp",
+                    type: .application,
+                    buildConfigurations: [TestBuildConfiguration("Debug", buildSettings: ["SWIFT_ACTIVE_COMPILATION_CONDITIONS": "MY_OTHER_APP"])],
+                    buildPhases: [TestSourcesBuildPhase([TestBuildFile("MyApp.swift")])]
+                )
+
+                let project = TestProject(
+                    "Test",
+                    groupTree: TestGroup("Test", children: [TestFile("MyApp.swift")]),
+                    targets: [appTarget, otherAppTarget]
+                )
+
+                try await testSession.sendPIF(TestWorkspace("Test", sourceRoot: tmpDir, projects: [project]))
+
+                let activeRunDestination = SWBRunDestinationInfo.macOS
+                var buildParameters = SWBBuildParameters(configuration: "Debug", activeRunDestination: activeRunDestination)
+                buildParameters.overrides = SWBSettingsOverrides()
+                buildParameters.overrides.commandLine = SWBSettingsTable()
+                // Set `ONLY_ACTIVE_ARCH`, otherwise we get two entries for each Swift file, one for each architecture
+                // with a different output path.
+                buildParameters.overrides.commandLine!.set(value: "YES", for: "ONLY_ACTIVE_ARCH")
+                var request = SWBBuildRequest()
+                request.add(target: SWBConfiguredTarget(guid: appTarget.guid, parameters: buildParameters))
+                request.add(target: SWBConfiguredTarget(guid: otherAppTarget.guid, parameters: buildParameters))
+
+                let buildDescriptionID = try await testSession.session.createBuildDescription(buildRequest: request)
+                let targetInfos = try await testSession.session.configuredTargets(buildDescription: buildDescriptionID, buildRequest: request)
+                let appTargetInfo = try #require(targetInfos.filter { $0.name == "MyApp" }.only)
+                let otherAppTargetInfo = try #require(targetInfos.filter { $0.name == "MyOtherApp" }.only)
+                let appSources = try #require(await testSession.session.sources(of: [appTargetInfo.guid], buildDescription: buildDescriptionID, buildRequest: request).only)
+                let myAppFile = try #require(Set(appSources.sourceFiles.map(\.path)).filter { $0.pathString.hasSuffix("MyApp.swift") }.only)
+
+                let appIndexSettings = try await testSession.session.indexCompilerArguments(of: myAppFile, in: appTargetInfo.guid, buildDescription: buildDescriptionID, buildRequest: request)
+                #expect(appIndexSettings.contains("-DMY_APP"))
+                #expect(!appIndexSettings.contains("-DMY_OTHER_APP"))
+                let otherAppIndexSettings = try await testSession.session.indexCompilerArguments(of: myAppFile, in: otherAppTargetInfo.guid, buildDescription: buildDescriptionID, buildRequest: request)
+                #expect(otherAppIndexSettings.contains("-DMY_OTHER_APP"))
+            }
+        }
+    }
+}
+
+fileprivate extension SWBBuildServiceSession {
+    func createBuildDescription(buildRequest: SWBBuildRequest) async throws -> SWBBuildDescriptionID {
+        var buildDescriptionID: SWBBuildDescriptionID?
+        let buildDescriptionOperation = try await self.createBuildOperationForBuildDescriptionOnly(
+            request: buildRequest,
+            delegate: TestBuildOperationDelegate()
+        )
+        for try await event in try await buildDescriptionOperation.start() {
+            guard case .reportBuildDescription(let info) = event else {
+                continue
+            }
+            guard buildDescriptionID == nil else {
+                Issue.record("Received multiple build description IDs")
+                continue
+            }
+            buildDescriptionID = SWBBuildDescriptionID(info.buildDescriptionID)
+        }
+        guard let buildDescriptionID else {
+            throw StubError.error("Failed to get build description ID")
+        }
+        return buildDescriptionID
+    }
+}