sampling
A tool that asks the host LLM for a completion. One factory, both protocol eras: sampling works on both eras with different APIs — push-style on 2025, inputRequired on 2026; the protocol carries the sampling/createMessage request differently but the user experience is the
same.
2025-era (--legacy, push-style) |
2026-07-28 (multi-round-trip) |
|---|---|
await ctx.mcpReq.requestSampling({ messages, maxTokens }) — the server pushes a sampling/createMessage request and awaits the answer in-line |
return inputRequired({ inputRequests: { summary: inputRequired.createMessage({ messages, maxTokens }) } }) — the client fulfils the embedded request and retries with the response attached |
The client registers one sampling/createMessage handler; on the 2026-07-28 leg the auto-fulfilment driver dispatches the embedded request to that same handler.
Push-style sampling is deprecated as of protocol revision 2026-07-28 (SEP-2577) but remains functional during the deprecation window.
Push-style sampling is exercised on stdio/legacy (createMcpHandler's stateless-legacy posture has no return path for the client's response POST — see ../legacy-routing/ for the sessionful composition); the http/legacy leg only verifies the initialize handshake.
2026-07-28 inputRequired.createMessage runs on both transports.
pnpm --filter @mcp-examples/sampling client # 2026-07-28 (inputRequired)
pnpm --filter @mcp-examples/sampling client -- --legacy # 2025 (push-style)
Source: examples/sampling/README.md