Adjust the read_file prompt based on whether partial reads are enabled (#3995)

Author: mrubens

src/core/prompts/__tests__/__snapshots__/system.test.ts.snap

@@ -76,6 +76,9 @@ describe("File-Based Custom System Prompt", () => {
 			undefined, // diffEnabled
 			undefined, // experiments
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		// Should contain default sections
@@ -110,6 +113,9 @@ describe("File-Based Custom System Prompt", () => {
 			undefined, // diffEnabled
 			undefined, // experiments
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		// Should contain role definition and file-based system prompt
@@ -153,6 +159,9 @@ describe("File-Based Custom System Prompt", () => {
 			undefined, // diffEnabled
 			undefined, // experiments
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		// Should contain custom role definition and file-based system prompt

src/core/prompts/__tests__/custom-system-prompt.test.ts

@@ -211,6 +211,9 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // diffEnabled
 			experiments,
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -231,6 +234,9 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // diffEnabled
 			experiments,
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -253,6 +259,9 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // diffEnabled
 			experiments,
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -273,6 +282,9 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // diffEnabled
 			experiments,
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -293,6 +305,9 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // diffEnabled
 			experiments,
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -313,6 +328,9 @@ describe("SYSTEM_PROMPT", () => {
 			true, // diffEnabled
 			experiments,
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).toContain("apply_diff")
@@ -334,6 +352,9 @@ describe("SYSTEM_PROMPT", () => {
 			false, // diffEnabled
 			experiments,
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).not.toContain("apply_diff")
@@ -355,6 +376,9 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // diffEnabled
 			experiments,
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).not.toContain("apply_diff")
@@ -403,6 +427,9 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // diffEnabled
 			undefined, // experiments
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).toContain("Language Preference:")
@@ -461,6 +488,9 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // diffEnabled
 			experiments,
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		// Role definition should be at the top
@@ -496,6 +526,9 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // diffEnabled
 			undefined, // experiments
 			false, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		// Role definition from promptComponent should be at the top
@@ -526,6 +559,9 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // diffEnabled
 			undefined, // experiments
 			false, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		// Should use the default mode's role definition
@@ -570,6 +606,9 @@ describe("addCustomInstructions", () => {
 			undefined, // diffEnabled
 			undefined, // experiments
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -590,6 +629,9 @@ describe("addCustomInstructions", () => {
 			undefined, // diffEnabled
 			undefined, // experiments
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -612,6 +654,9 @@ describe("addCustomInstructions", () => {
 			undefined, // diffEnabled
 			undefined, // experiments
 			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).toContain("Creating an MCP Server")
@@ -635,12 +680,38 @@ describe("addCustomInstructions", () => {
 			undefined, // diffEnabled
 			undefined, // experiments
 			false, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			undefined, // partialReadsEnabled
 		)
 
 		expect(prompt).not.toContain("Creating an MCP Server")
 		expect(prompt).toMatchSnapshot()
 	})
 
+	it("should include partial read instructions when partialReadsEnabled is true", async () => {
+		const prompt = await SYSTEM_PROMPT(
+			mockContext,
+			"/test/path",
+			false, // supportsComputerUse
+			undefined, // mcpHub
+			undefined, // diffStrategy
+			undefined, // browserViewportSize
+			defaultModeSlug, // mode
+			undefined, // customModePrompts
+			undefined, // customModes,
+			undefined, // globalCustomInstructions
+			undefined, // diffEnabled
+			undefined, // experiments
+			true, // enableMcpServerCreation
+			undefined, // language
+			undefined, // rooIgnoreInstructions
+			true, // partialReadsEnabled
+		)
+
+		expect(prompt).toMatchSnapshot()
+	})
+
 	it("should prioritize mode-specific rules for code mode", async () => {
 		const instructions = await addCustomInstructions("", "", "/test/path", defaultModeSlug)
 		expect(instructions).toMatchSnapshot()

src/core/prompts/__tests__/system.test.ts

@@ -45,6 +45,7 @@ async function generatePrompt(
 	enableMcpServerCreation?: boolean,
 	language?: string,
 	rooIgnoreInstructions?: string,
+	partialReadsEnabled?: boolean,
 ): Promise<string> {
 	if (!context) {
 		throw new Error("Extension context is required for generating system prompt")
@@ -82,6 +83,7 @@ ${getToolDescriptionsForMode(
 	mcpHub,
 	customModeConfigs,
 	experiments,
+	partialReadsEnabled,
 )}
 
 ${getToolUseGuidelinesSection()}
@@ -119,6 +121,7 @@ export const SYSTEM_PROMPT = async (
 	enableMcpServerCreation?: boolean,
 	language?: string,
 	rooIgnoreInstructions?: string,
+	partialReadsEnabled?: boolean,
 ): Promise<string> => {
 	if (!context) {
 		throw new Error("Extension context is required for generating system prompt")
@@ -185,5 +188,6 @@ ${customInstructions}`
 		enableMcpServerCreation,
 		language,
 		rooIgnoreInstructions,
+		partialReadsEnabled,
 	)
 }

src/core/prompts/system.ts

@@ -56,6 +56,7 @@ export function getToolDescriptionsForMode(
 	mcpHub?: McpHub,
 	customModes?: ModeConfig[],
 	experiments?: Record<string, boolean>,
+	partialReadsEnabled?: boolean,
 ): string {
 	const config = getModeConfig(mode, customModes)
 	const args: ToolArgs = {
@@ -64,6 +65,7 @@ export function getToolDescriptionsForMode(
 		diffStrategy,
 		browserViewportSize,
 		mcpHub,
+		partialReadsEnabled,
 	}
 
 	const tools = new Set<string>()

src/core/prompts/tools/index.ts

@@ -1,25 +1,51 @@
 import { ToolArgs } from "./types"
 
 export function getReadFileDescription(args: ToolArgs): string {
-	return `## read_file
-Description: Request to read the contents of a file at the specified path. Use this when you need to examine the contents of an existing file you do not know the contents of, for example to analyze code, review text files, or extract information from configuration files. The output includes line numbers prefixed to each line (e.g. "1 | const x = 1"), making it easier to reference specific lines when creating diffs or discussing code. By specifying start_line and end_line parameters, you can efficiently read specific portions of large files without loading the entire file into memory. Automatically extracts raw text from PDF and DOCX files. May not be suitable for other types of binary files, as it returns the raw content as a string.
+	// Base description without partial read instructions
+	let description = `## read_file
+Description: Request to read the contents of a file at the specified path. Use this when you need to examine the contents of an existing file you do not know the contents of, for example to analyze code, review text files, or extract information from configuration files. The output includes line numbers prefixed to each line (e.g. "1 | const x = 1"), making it easier to reference specific lines when creating diffs or discussing code.`
+
+	// Add partial read instructions only when partial reads are active
+	if (args.partialReadsEnabled) {
+		description += ` By specifying start_line and end_line parameters, you can efficiently read specific portions of large files without loading the entire file into memory.`
+	}
+
+	description += ` Automatically extracts raw text from PDF and DOCX files. May not be suitable for other types of binary files, as it returns the raw content as a string.
 Parameters:
-- path: (required) The path of the file to read (relative to the current workspace directory ${args.cwd})
+- path: (required) The path of the file to read (relative to the current workspace directory ${args.cwd})`
+
+	// Add start_line and end_line parameters only when partial reads are active
+	if (args.partialReadsEnabled) {
+		description += `
 - start_line: (optional) The starting line number to read from (1-based). If not provided, it starts from the beginning of the file.
-- end_line: (optional) The ending line number to read to (1-based, inclusive). If not provided, it reads to the end of the file.
+- end_line: (optional) The ending line number to read to (1-based, inclusive). If not provided, it reads to the end of the file.`
+	}
+
+	description += `
 Usage:
 <read_file>
-<path>File path here</path>
+<path>File path here</path>`
+
+	// Add start_line and end_line in usage only when partial reads are active
+	if (args.partialReadsEnabled) {
+		description += `
 <start_line>Starting line number (optional)</start_line>
-<end_line>Ending line number (optional)</end_line>
+<end_line>Ending line number (optional)</end_line>`
+	}
+
+	description += `
 </read_file>
 
 Examples:
 
 1. Reading an entire file:
 <read_file>
 <path>frontend-config.json</path>
-</read_file>
+</read_file>`
+
+	// Add partial read examples only when partial reads are active
+	if (args.partialReadsEnabled) {
+		description += `
 
 2. Reading the first 1000 lines of a large log file:
 <read_file>
@@ -42,4 +68,7 @@ Examples:
 </read_file>
 
 Note: When both start_line and end_line are provided, this tool efficiently streams only the requested lines, making it suitable for processing large files like logs, CSV files, and other large datasets without memory issues.`
+	}
+
+	return description
 }

src/core/prompts/tools/read-file.ts

@@ -8,4 +8,5 @@ export type ToolArgs = {
 	browserViewportSize?: string
 	mcpHub?: McpHub
 	toolOptions?: any
+	partialReadsEnabled?: boolean
 }

src/core/prompts/tools/types.ts

@@ -1451,18 +1451,19 @@ export class Task extends EventEmitter<ClineEvents> {
 
 		const rooIgnoreInstructions = this.rooIgnoreController?.getInstructions()
 
+		const state = await this.providerRef.deref()?.getState()
 		const {
 			browserViewportSize,
 			mode,
+			customModes,
 			customModePrompts,
 			customInstructions,
 			experiments,
 			enableMcpServerCreation,
 			browserToolEnabled,
 			language,
-		} = (await this.providerRef.deref()?.getState()) ?? {}
-
-		const { customModes } = (await this.providerRef.deref()?.getState()) ?? {}
+			maxReadFileLine,
+		} = state ?? {}
 
 		return await (async () => {
 			const provider = this.providerRef.deref()
@@ -1487,6 +1488,7 @@ export class Task extends EventEmitter<ClineEvents> {
 				enableMcpServerCreation,
 				language,
 				rooIgnoreInstructions,
+				maxReadFileLine !== -1,
 			)
 		})()
 	}

src/core/task/Task.ts

@@ -20,6 +20,7 @@ export const generateSystemPrompt = async (provider: ClineProvider, message: Web
 		enableMcpServerCreation,
 		browserToolEnabled,
 		language,
+		maxReadFileLine,
 	} = await provider.getState()
 
 	const diffStrategy = new MultiSearchReplaceDiffStrategy(fuzzyMatchThreshold)
@@ -67,6 +68,7 @@ export const generateSystemPrompt = async (provider: ClineProvider, message: Web
 		enableMcpServerCreation,
 		language,
 		rooIgnoreInstructions,
+		maxReadFileLine !== -1,
 	)
 
 	return systemPrompt