feat: Add prompt support with typed argument handling #351

snowmead · 2025-08-04T21:48:50Z

This PR introduces a comprehensive prompt system for the Rust SDK, adding #[prompt], #[prompt_router], and #[prompt_handler] macros that enable MCP servers to provide reusable prompt templates.

Motivation and Context

This change enables MCP servers to define discoverable prompt templates that LLMs can invoke with type-safe parameters. It provides a standardized way to define, route, and handle prompts, improving the interaction between LLMs and server-side prompt templates.

How Has This Been Tested?

Added comprehensive unit tests for the prompt macro functionality
Tested doc comment description extraction from prompt handlers
Verified prompt attribute generation and async function transformation
Tested automatic JSON schema generation from Rust types
Included example implementations demonstrating usage patterns

Breaking Changes

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

- Implement #[prompt], #[prompt_router], and #[prompt_handler] macros - Add automatic JSON schema generation from Rust types for arguments - Support flexible async handler signatures with automatic adaptation - Create PromptRouter for efficient prompt dispatch - Include comprehensive tests and example implementation This enables MCP servers to provide reusable prompt templates that LLMs can discover and invoke with strongly-typed parameters, similar to the existing tool system but optimized for prompt use cases. 🤖 Generated with Claude Code Co-Authored-By: Claude <[email protected]>

- Replace Arguments<T> with Parameters<T> for consistent API - Create shared common module for tool/prompt utilities - Modernize async handling with futures::future::BoxFuture - Move cached_schema_for_type to common module for reuse - Update error types from rmcp::Error to rmcp::ErrorData - Add comprehensive trait implementations for parameter extraction 🤖 Generated with Claude Code Co-Authored-By: Claude <[email protected]>

Copilot

Pull Request Overview

This PR introduces a comprehensive prompt system for the Rust SDK, adding support for #[prompt], #[prompt_router], and #[prompt_handler] macros that enable MCP servers to provide reusable prompt templates with type-safe parameter handling.

Adds prompt handling infrastructure with macro support for defining, routing, and handling prompts
Introduces automatic JSON schema generation from Rust types for prompt arguments
Provides comprehensive test coverage for prompt functionality and examples

Reviewed Changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
examples/servers/src/common/counter.rs	Demonstrates prompt implementation with example prompts that take typed arguments
examples/servers/README.md	Documents the new prompt standard I/O server example
examples/servers/Cargo.toml	Adds new prompt example entries and tokio-util dependency
crates/rmcp/tests/test_prompt_*.rs	Comprehensive test suite for prompt macros, routers, and handlers
crates/rmcp/src/service.rs	Updates BoxFuture lifetimes from 'static to '_ for better lifetime management
crates/rmcp/src/handler/server/*.rs	Core prompt handling infrastructure with context, routing, and parameter extraction
crates/rmcp-macros/src/*.rs	Macro implementations for #[prompt], #[prompt_router], and #[prompt_handler]

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Copilot · 2025-08-14T07:09:59Z

crates/rmcp/src/handler/server/common.rs

+    let object = serde_json::to_value(schema).expect("failed to serialize schema");
+    match object {
+        serde_json::Value::Object(object) => object,
+        _ => panic!("unexpected schema value"),


The panic message should be more descriptive. Consider: panic!("Schema serialization produced non-object value: expected JSON object but got {:?}", object)

Suggested change

_ => panic!("unexpected schema value"),

_ => panic!("Schema serialization produced non-object value: expected JSON object but got {:?}", object),

Copilot · 2025-08-14T07:10:00Z

crates/rmcp/src/handler/server/prompt.rs

+            None
+        } else {
+            Some(arguments)
+        }


[nitpick] The function returns None when no properties are found, but it might be clearer to return Some(vec![]) for an empty argument list vs None for no schema. Consider documenting this behavior or making it more explicit.

Suggested change

}

// Always return Some(arguments), even if empty

Some(arguments)

Copilot · 2025-08-14T07:10:00Z

examples/servers/src/common/counter.rs

@@ -97,7 +177,7 @@ impl ServerHandler for Counter {
                .enable_tools()
                .build(),
            server_info: Implementation::from_build_env(),
-            instructions: Some("This server provides a counter tool that can increment and decrement values. The counter starts at 0 and can be modified using the 'increment' and 'decrement' tools. Use 'get_value' to check the current count.".to_string()),
+            instructions: Some("This server provides counter tools and prompts. Tools: increment, decrement, get_value, say_hello, echo, sum. Prompts: example_prompt (takes a message), counter_analysis (analyzes counter state with a goal).".to_string()),


This hardcoded instruction string should be generated dynamically from the available tools and prompts to ensure it stays in sync when tools/prompts are added or removed.

Suggested change

instructions: Some("This server provides counter tools and prompts. Tools: increment, decrement, get_value, say_hello, echo, sum. Prompts: example_prompt (takes a message), counter_analysis (analyzes counter state with a goal).".to_string()),

instructions: Some(Self::generate_instructions()),

4t145 · 2025-08-14T07:21:15Z

crates/rmcp/src/handler/server/tool.rs

-///
-/// Note: This is a basic validation that only checks type compatibility.
-/// For full JSON Schema validation, a dedicated validation library would be needed.
-pub fn validate_against_schema(


It looks like you forgot to move this to common.rs

And this implementation looks not good enought, type of json schema could be other value like "integer" or multiple types. It's my fault for miss this point before merge it. But it's another issue.

4t145 · 2025-08-14T07:48:26Z

crates/rmcp/src/service.rs

@@ -162,12 +162,12 @@ pub trait DynService<R: ServiceRole>: Send + Sync {
        &self,
        request: R::PeerReq,
        context: RequestContext<R>,
-    ) -> BoxFuture<Result<R::Resp, McpError>>;
+    ) -> BoxFuture<'_, Result<R::Resp, McpError>>;


Will there be compile error if I remove '_?

4t145 · 2025-08-14T07:59:36Z

crates/rmcp/src/handler/server/common.rs

+/// Parameter Extractor
+#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
+#[serde(transparent)]
+pub struct Parameters<P>(pub P);


We have json.rs under crates/rmcp/src/handler/server/wrapper, should we move those wrapper to there too?

4t145 · 2025-08-14T08:05:19Z

examples/servers/Cargo.toml

@@ -76,6 +77,10 @@ path = "src/complex_auth_sse.rs"
 name = "servers_simple_auth_sse"
 path = "src/simple_auth_sse.rs"

+[[example]]
+name = "servers_prompt_stdio"
+path = "src/prompt_stdio.rs"


exmaples added here, but no corresponded file.

4t145 · 2025-08-14T08:05:31Z

examples/servers/Cargo.toml

@@ -87,3 +92,7 @@ path = "src/sampling_stdio.rs"
 [[example]]
 name = "servers_structured_output"
 path = "src/structured_output.rs"
+
+[[example]]
+name = "servers_prompt_with_extractors"


exmaples added here, but no corresponded file.

4t145 · 2025-08-14T08:07:20Z

And you can use just fix before commit, this will fix the format and clippy error.

snowmead and others added 2 commits August 4, 2025 17:43

Merge branch 'modelcontextprotocol:main' into feature/prompt-support

c88a7c1

4t145 requested a review from Copilot August 14, 2025 07:08

Copilot AI reviewed Aug 14, 2025

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feat: Add prompt support with typed argument handling #351

feat: Add prompt support with typed argument handling #351

snowmead commented Aug 4, 2025 •

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	_ => panic!("unexpected schema value"),
	_ => panic!("Schema serialization produced non-object value: expected JSON object but got {:?}", object),

	}
	// Always return Some(arguments), even if empty
	Some(arguments)

	instructions: Some("This server provides counter tools and prompts. Tools: increment, decrement, get_value, say_hello, echo, sum. Prompts: example_prompt (takes a message), counter_analysis (analyzes counter state with a goal).".to_string()),
	instructions: Some(Self::generate_instructions()),

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Motivation and Context

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