[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
mcp	==2.2.0 → ==2.3.0

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Release Notes

modelcontextprotocol/python-sdk (mcp)

v2.3.0

Compare Source

pip install -U mcp. Docs: https://py.sdk.modelcontextprotocol.io/

Mostly fixes, plus three new options. A few things behave differently, so skim these first:

Behaviour changes

httpx2>=2.10.0 is now required (#​3600)

• It was >=2.5.0. The new max_sse_event_size option needs it.
• Nothing to do unless you pin httpx2 below 2.10.

A tool with an invalid x-mcp-header annotation fails at registration (#​3620)

• @mcp.tool(), add_tool and Tool.from_function raise InvalidSignature, naming the tool and the problem.
• Until now the server started, and 2026-07-28 clients silently dropped the tool from their listing.
• Refused: anything other than a plain str, int or bool parameter (so also str | None, float, lists and enums), a header name that isn't a valid token, and two names that differ only by case.
• For an optional header parameter, give the schema directly: Annotated[str | None, WithJsonSchema({"type": "string", "x-mcp-header": "Region"})] = None.

Empty _meta and params are no longer sent (#​3628)

• On 2025-11-25 and earlier connections, 2.x sent "_meta": {} on every request. Some servers reject that. It is now left out, as in v1.
• ping and list requests without a cursor go out with no params member.
• On the receiving side ctx.meta is None rather than {}, and middleware sees ctx.params as None for a request without params.
• 2026-07-28 connections are unchanged.

initialize leaves out experimental when none is configured (#​3614)

• It used to send "experimental": {}. server/discover already left it out.
• Client code reading capabilities.experimental on a legacy connection should handle None.

Mcp-Param-* validation looks the tool up by name (#​3630)

• MCPServer no longer runs tools/list for every tools/call, so middleware no longer sees that extra request.
• The registered schema is what gets checked. Middleware that filters or rewrites tools/list no longer affects it.

An interactive OAuth login no longer counts against request timeouts (#​3635)

• The timeout pauses while OAuthClientProvider waits on redirect_handler and callback_handler.
• This fixes Client(mode="auto") settling on 2025-11-25 when the login took longer than 10 seconds.
• A request timeout no longer ends a login nobody finishes. Put a limit inside callback_handler if you need one.

New

• max_sse_event_size= on streamable_http_client and StreamableHttpParameters. The default stays 1 MiB per SSE event; raise it, or pass None, for larger tool results (#​3600).
• MCPServer(subscriptions=False) stops serving subscriptions/listen and advertises listChanged and subscribe as false (#​3626).
• Server(get_tool_input_schema=...) lets a low-level server supply a tool's schema for header validation without running its tools/list handler (#​3630).
• Client.call_tool re-lists the tools and retries once after a HeaderMismatch (-32020) rejection (#​3627).

Fixes

• ctx: Context[AppState] works on prompts and resource templates, not only on tools (#​3624).
• An explicit "structuredContent": null is checked against the output schema instead of being treated as missing (#​3621).
• A progress_callback that raises no longer fails the call on an in-process Client(server) (#​3623).
• Client OpenTelemetry spans record JSON-RPC error responses. With mode="auto", connecting to a server without server/discover now shows one ERROR span for the probe (#​3629).
• stdio_client resolves the executable off the event loop on Windows (#​3510).

Docs

• New pages: Cancellation and Header parameters, plus a middleware tutorial.
• All twelve translations are refreshed (#​3636).

What's Changed

• Detect event-loop blocking in tests by @​Kludex in #​3510
• Bump httpcore2 from 2.5.0 to 2.10.0 by @​dependabot[bot] in #​3482
• Ask cubic for a review when the intake gate lets a PR back in by @​maxisbey in #​3489
• docs: remove v2 notice from top of README by @​claude[bot] in #​3604
• Bump anyio from 4.10.0 to 4.14.2 by @​dependabot[bot] in #​3547
• Make the deeply nested body test independent of stack size by @​maxisbey in #​3610
• Fall back to an NTFS junction when the symlink escape test can't create a symlink by @​maxisbey in #​3609
• Group Dependabot security updates for uv dependencies by @​Kludex in #​3611
• Expose an SSE event size limit in Streamable HTTP clients by @​Kludex in #​3600
• Bump the github-actions group with 5 updates by @​dependabot[bot] in #​3612
• docs: add a middleware tutorial that refuses tool calls by @​maxisbey in #​3613
• Omit an unset experimental capability from the initialize result by @​maxisbey in #​3614
• Document when a caller-supplied request id can be minted again by @​maxisbey in #​3619
• Document the timeout a hand-built httpx2 client needs by @​maxisbey in #​3618
• Reject a tool with an invalid x-mcp-header annotation at registration by @​maxisbey in #​3620
• Validate an explicit null structuredContent against the output schema by @​maxisbey in #​3621
• Contain a raising progress callback on the in-process dispatcher by @​maxisbey in #​3623
• Keep the live Context when a prompt or template annotates Context[T] by @​maxisbey in #​3624
• Describe the ID-JAG confidential-client rule as SDK policy, not a SEP-990 requirement by @​maxisbey in #​3622
• Let MCPServer opt out of serving subscriptions/listen by @​maxisbey in #​3626
• Document how a handler deals with cancellation by @​maxisbey in #​3625
• Omit an empty _meta and empty params from outbound requests by @​maxisbey in #​3628
• Record JSON-RPC error responses on the client OpenTelemetry span by @​maxisbey in #​3629
• Retry a tool call once after a HeaderMismatch rejection by @​maxisbey in #​3627
• Look the tool schema up by name for Mcp-Param-* validation instead of running tools/list by @​maxisbey in #​3630
• Bump urllib3 from 2.7.0 to 2.8.0 by @​dependabot[bot] in #​3607
• Let a newer Deploy Docs run cancel the one in progress by @​maxisbey in #​3633
• Link What's new to the Header parameters page by @​maxisbey in #​3632
• Keep inline-snapshot disabled when pytest runs in a terminal by @​maxisbey in #​3634
• Stop counting an interactive OAuth login against request timeouts by @​maxisbey in #​3635
• docs: refresh translations for recent English changes by @​maxisbey in #​3636

Full Changelog: modelcontextprotocol/python-sdk@v2.2.0...v2.3.0

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