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Filename Latest commit message Latest commit date
Robert Findley 3cf9f9908d
 mcp: implement sampling with tools (#699) 
Summary

Add support for tool use within sampling requests, as described in the
MCP 2025-11-25 spec's sampling.tools capability.
  New types

  Content types:
- ToolUseContent — represents a tool invocation request from the
assistant
- ToolResultContent — represents the result of a tool invocation, with
nested []Content for the result blocks

  Capability types:
  - SamplingCapabilities gains Tools and Context sub-fields
  - SamplingToolsCapabilities, SamplingContextCapabilities

  Tool-enabled sampling (parallel tool calls):
- CreateMessageWithToolsParams with SamplingMessageV2 (supports array
content)
  - CreateMessageWithToolsResult (supports array content)
  - ToolChoice — controls tool invocation mode (auto, required, none)
  - ServerSession.CreateMessageWithTools
  - ClientOptions.CreateMessageWithToolsHandler

  Design

Following the TypeScript SDK's pattern, tool-enabled sampling uses
separate types from basic sampling to avoid breaking the existing API.
The basic CreateMessage/CreateMessageResult path
   is unchanged.

Both paths share the same wire method (sampling/createMessage) and go
through the method info table. The table uses the broader
CreateMessageWithToolsResult type internally;
CreateMessage downconverts (erroring if multiple content blocks are
returned). This is documented as a rough edge to unify in v2.

Setting CreateMessageWithToolsHandler automatically infers the
sampling.tools capability. It is a panic to set both
CreateMessageHandler and CreateMessageWithToolsHandler.

  References

-
https://modelcontextprotocol.io/specification/2025-11-25/client/sampling
- TypeScript SDK: CreateMessageResultWithToolsSchema /
CreateMessageRequestParamsWithTools

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
2026-02-17 12:07:08 +01:00
..
client.md mcp: add Capabilities fields to ServerOptions and ClientOptions (#713) 2025-12-11 20:17:46 -05:00
index.html docs: add GitHub Pages redirect to latest release documentation (#702) 2025-12-16 15:21:03 -08:00
protocol.md internal/docs: document UserID for session hijacking prevention (#697) 2025-12-08 15:25:34 -05:00
README.md docs: document known rough edges (#609) 2025-10-29 10:57:45 -04:00
rough_edges.md mcp: implement sampling with tools (#699) 2026-02-17 12:07:08 +01:00
server.md perf: add schema caching to avoid repeated reflection (#685) 2026-01-20 20:16:46 -05:00
troubleshooting.md mcp: fix broken client root capabilities (#698) 2025-12-11 10:16:56 -05:00

README.md

Features

These docs mirror the official MCP spec. Use the index below to learn how the SDK implements a particular aspect of the protocol.

Base Protocol

  1. Lifecycle (Clients, Servers, and Sessions).
  2. Transports
    1. Stdio transport
    2. Streamable transport
    3. Custom transports
  3. Authorization
  4. Security
  5. Utilities
    1. Cancellation
    2. Ping
    3. Progress

Client Features

  1. Roots
  2. Sampling
  3. Elicitation

Server Features

  1. Prompts
  2. Resources
  3. Tools
  4. Utilities
    1. Completion
    2. Logging
    3. Pagination

TroubleShooting

See troubleshooting.md for a troubleshooting guide.

Rough edges

See rough_edges.md for a list of rough edges or API oversights that can't be addressed due to our compatibility promise. We'll revisit these if/when we move to a v2 of the SDK.