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Bumps mcp from 2.2.0 to 2.3.0.

Release notes

Sourced from mcp's releases.

v2.3.0

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).

... (truncated)

Commits

• 2118f14 docs: refresh translations for recent English changes (#3636)
• ed9b2d6 Stop counting an interactive OAuth login against request timeouts (#3635)
• d5cebd1 Keep inline-snapshot disabled when pytest runs in a terminal (#3634)
• c15566c Link What's new to the Header parameters page (#3632)
• 4d29994 Let a newer Deploy Docs run cancel the one in progress (#3633)
• 0acea60 Bump urllib3 from 2.7.0 to 2.8.0 (#3607)
• c54075c Look the tool schema up by name for Mcp-Param-* validation instead of running...
• 9afccae Retry a tool call once after a HeaderMismatch rejection (#3627)
• cafa33b Record JSON-RPC error responses on the client OpenTelemetry span (#3629)
• 0b2fd3e Omit an empty _meta and empty params from outbound requests (#3628)
• Additional commits viewable in compare view

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