fix: send params as empty object for list methods without cursor #1453

felixweinberger · 2025-10-09T14:17:08Z

Motivation and Context

Some external MCP servers implement strict JSON-RPC validation requiring the params field to always be present. Previously, the Python SDK omitted params entirely when cursor=None, causing validation errors. There is no way to force params={} with the current implementation of list_tools(), making it not possible to interact with these servers.

This change allows sending params: {} by allowing the caller to specify a full types.PaginatedRequestParams rather than just cursor, matching TypeScript SDK flexibility and allowing more compatibility with strict servers. We achieve this by introducing a new optional param params: types.PaginatedRequestParams | None = None which will be the new way to interact with this API.

How Has This Been Tested?

Added a test demonstrating the specific behavior as well the new param.
Refactored the existing tests to be parameterized.

Breaking Changes

This change is fully backwards compatible as existing behavior stays the same and the new param is completely optional.

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

Additional context

Some external MCP servers implement strict JSON-RPC validation requiring the params field to always be present. Previously, the Python SDK omitted params entirely when cursor=None, causing validation errors. Now sends params: {} when no cursor is provided, matching TypeScript SDK behavior and fixing compatibility with strict servers. Reported-by: justin-yi-wang

felixweinberger · 2025-10-09T15:42:16Z

Re-evaluating the approach here, as we're basically making the params={} the default behavior with this when no cursor is supplied. The TS SDK allows both via:

// explicit {} param
const result = await client.listTools({});

// undefined param, gets ommited by JSON.stringify()
const result = await client.listTools();

Whereas with this change we would now always force list_tools(params={}) in Python. Maybe the better approach is to allow both {} and None in Python on list_tools() somehow.

The spec defines ListToolRequest with both fields as optional:

interface ListToolsRequest {
  method: “tools/list”;
  params?: { cursor?: string };
}

https://modelcontextprotocol.io/specification/2025-06-18/schema#listtoolsrequest

An alternative solution could be to change the signature of list_tools to something like:

  async def list_tools(
      self,
      cursor: str | None = None, # deprecated
      *,
      params: types.PaginatedRequestParams | None = None,
  ) -> types.ListToolsResult:

Which would be more complete and equivalent to TS capabilities here: https://github.com/modelcontextprotocol/typescript-sdk/blob/f4b8a48ded019a54a38d3d150a013427d6cbdbc6/src/client/index.ts#L500-L514

Deprecate the cursor parameter in list_tools, list_prompts, list_resources, and list_resource_templates methods, replacing it with a new params parameter that accepts PaginatedRequestParams. This change maintains complete backwards compatibility while providing opt-in support for strict MCP servers that require the params field to always be present in JSON-RPC requests (even if empty). When params is not provided or is None, the SDK continues to omit the params field entirely, matching the previous behavior. The cursor parameter now issues a DeprecationWarning directing developers to use the new params parameter. This matches the TypeScript SDK's API design. Reported-by: justin-yi-wang

Add comprehensive tests for the new params parameter across all four list methods (list_tools, list_resources, list_prompts, list_resource_templates). Tests verify: 1. params parameter works correctly when omitted, set to None, or set to empty 2. params parameter correctly passes cursor values 3. params parameter takes precedence over deprecated cursor parameter when both are provided, ensuring a safe migration path for existing code These tests ensure the backwards compatibility guarantees are preserved and prevent regressions in precedence behavior.

Replace 13 individual test functions with 3 parametrized test functions that cover all four list methods (list_tools, list_resources, list_prompts, list_resource_templates). Changes: - Created full_featured_server fixture with tools, resources, prompts, and templates - test_list_methods_cursor_parameter: parametrized version of 4 cursor tests - test_list_methods_params_parameter: parametrized version of 4 params tests - test_list_methods_params_takes_precedence_over_cursor: parametrized precedence tests - Kept test_list_tools_with_strict_server_validation separate (different scenario) Result: Reduced from 600+ lines to ~240 lines while maintaining identical coverage (13 test cases, all passing).

felixweinberger · 2025-10-09T17:17:08Z

Updated this PR with the approach described in the above comment.

This PR is probably easier to review looking at each commit, as I also took the chance to refactor tests for less repetition in the last commit.

src/mcp/client/session.py

maxisbey

I think doing something like this would help as it gives errors in the IDE if you use the wrong signature:

    @overload
    async def list_resources(self, cursor: str) -> types.ListResourcesResult: ...

    @overload
    async def list_resources(self, *, params: types.PaginatedRequestParams) -> types.ListResourcesResult: ...

    @overload
    async def list_resources(self) -> types.ListResourcesResult: ...

    @deprecated
    async def list_resources(
        self,
        cursor: str | None = None,
        *,
        params: types.PaginatedRequestParams | None = None,
    ) -> types.ListResourcesResult:
        """Send a resources/list request.

        Args:
            cursor: Simple cursor string for pagination (deprecated, use params instead)
            params: Full pagination parameters including cursor and any future fields
        """
        if params is not None and cursor is not None:
            raise ValueError("Cannot specify both cursor and params")

        if params is not None:
            request_params = params
        elif cursor is not None:
            request_params = types.PaginatedRequestParams(cursor=cursor)
        else:
            request_params = None

        return await self.send_request(
            types.ClientRequest(types.ListResourcesRequest(params=request_params)),
            types.ListResourcesResult,
        )

For testing here's a script which will show errors in pyright and your IDE:

"""Test file to verify overload typing works correctly."""

import asyncio

from mcp.client.session import ClientSession
from mcp.types import PaginatedRequestParams


async def test_overload_typing() -> None:
    """Test different ways of calling list_resources."""
    # This is just for type checking, we don't actually run it
    session: ClientSession = None  # type: ignore

    # Should work: no arguments
    result1 = await session.list_resources()

    # Should work: cursor as positional string
    result2 = await session.list_resources("some_cursor")

    # Should work: cursor as keyword string
    result3 = await session.list_resources(cursor="some_cursor")

    # Should work: params as keyword argument
    result4 = await session.list_resources(params=PaginatedRequestParams(cursor="some_cursor"))

    # Should ERROR: both cursor and params
    result5 = await session.list_resources(cursor="some_cursor", params=PaginatedRequestParams(cursor="other"))

    # Should ERROR: cursor=None (overload expects str, not str | None)
    result6 = await session.list_resources(cursor=None)

    # Should ERROR: params as positional
    result7 = await session.list_resources(PaginatedRequestParams(cursor="some_cursor"))


if __name__ == "__main__":
    asyncio.run(test_overload_typing())

@overload

Implements feedback from maxisbey on PR #1453. This change improves type safety and deprecation handling for list methods (list_tools, list_resources, list_prompts, list_resource_templates): - Add @overload decorators with three signatures to provide clear IDE typing: - cursor: str (positional argument) - params: PaginatedRequestParams (keyword-only argument) - no arguments - Replace warnings.warn() with @deprecated decorator from typing_extensions for cleaner deprecation signaling - Add validation to raise ValueError when both cursor and params are provided, preventing ambiguous parameter combinations - Update tests to expect ValueError when both parameters are specified This ensures the Python SDK has type checking equivalent to the TypeScript SDK and provides better developer experience through IDE assistance and clear deprecation messaging.

felixweinberger · 2025-10-13T16:45:32Z

@maxisbey implemented the @overload approach in commit on top.

However I think the decorator was in the wrong place - it should only be on the old signature, i.e. list_tools(self, cursor: str | None).

I.e. I think the type errors should look like this (what it looks like with the current branch):

What this looks like on hover:

@overload

Implements feedback from maxisbey on PR #1453. This change improves type safety and deprecation handling for list methods (list_tools, list_resources, list_prompts, list_resource_templates): - Add @overload decorators with three signatures to provide clear IDE typing: - cursor: str (positional argument) - params: PaginatedRequestParams (keyword-only argument) - no arguments - Replace warnings.warn() with @deprecated decorator from typing_extensions for cleaner deprecation signaling - Add validation to raise ValueError when both cursor and params are provided, preventing ambiguous parameter combinations - Update tests to expect ValueError when both parameters are specified This ensures the Python SDK has type checking equivalent to the TypeScript SDK and provides better developer experience through IDE assistance and clear deprecation messaging.

@overload

Implements feedback from maxisbey on PR #1453. This change improves type safety and deprecation handling for list methods (list_tools, list_resources, list_prompts, list_resource_templates): - Add @overload decorators with three signatures to provide clear IDE typing: - cursor: str (positional argument) - params: PaginatedRequestParams (keyword-only argument) - no arguments - Replace warnings.warn() with @deprecated decorator from typing_extensions for cleaner deprecation signaling - Add validation to raise ValueError when both cursor and params are provided, preventing ambiguous parameter combinations - Update tests to expect ValueError when both parameters are specified This ensures the Python SDK has type checking equivalent to the TypeScript SDK and provides better developer experience through IDE assistance and clear deprecation messaging.

@deprecated

See: https://docs.python.org/3.13/library/warnings.html#warnings.deprecated @deprecated combined with @overload is specifically called out to be placed _after_ the @overload.

…elcontextprotocol#1453)

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flow with JWT and Basic auth (modelcontextprotocol#1663) Co-authored-by: Claude <noreply@anthropic.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * feat: backwards-compatible create_message overloads for SEP-1577 (modelcontextprotocol#1713) * Merge commit from fork * Auto-enable DNS rebinding protection for localhost servers When a FastMCP server is created with host="127.0.0.1" or "localhost" and no explicit transport_security is provided, automatically enable DNS rebinding protection. 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When host="::1", protection is now auto-enabled with appropriate allowed hosts ([::1]:*) and origins (http://[::1]:*). * Fix import ordering in test file * chore: update LATEST_PROTOCOL_VERSION to 2025-11-25 (modelcontextprotocol#1715) * fix: add lifespan context manager to StreamableHTTP mounting examples (modelcontextprotocol#1669) Co-authored-by: TheMailmans <tyler@example.com> Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com> * fix: handle ClosedResourceError in StreamableHTTP message router (modelcontextprotocol#1384) Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com> Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com> * fix: skip priming events and close_sse_stream for old protocol versions (modelcontextprotocol#1719) * refactor(auth): remove unused _register_client method (modelcontextprotocol#1748) * [MCP-266] Add tests for Gumloop server extensions * Fix uv workspace config for gumloop-mcp package name * Sync with upstream MCP SDK and fix merge conflicts * Fix tool cache timing and missing properties check in server.py * Fix coverage and add proper type annotations for Gumloop extensions * Version up * Skip README code example tests (Gumloop README has no code snippets) --------- Signed-off-by: San Nguyen <vinhsannguyen91@gmail.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> Co-authored-by: yurikunash <143175350+yurikunash@users.noreply.github.com> Co-authored-by: Pamela Fox <pamela.fox@gmail.com> Co-authored-by: Inna Harper <inna.hrpr@gmail.com> Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com> Co-authored-by: Ian Davenport <49379192+davenpi@users.noreply.github.com> Co-authored-by: Dagang Wei <functicons@gmail.com> Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> Co-authored-by: Stanley Law <stanleylkal@gmail.com> Co-authored-by: Luca Chang <131398524+LucaButBoring@users.noreply.github.com> Co-authored-by: leweng <leweng@nvidia.com> Co-authored-by: Clare Liguori <liguori@amazon.com> Co-authored-by: lukacf <luka@peltarion.com> Co-authored-by: ihrpr <inna@anthropic.com> Co-authored-by: Tapan Chugh <chugh.tapan@gmail.com> Co-authored-by: Tapan Chugh <tapanc@cs.washington.edu> Co-authored-by: Yann Jouanin <4557670+yannj-fr@users.noreply.github.com> Co-authored-by: Paul Carleton <paulcarletonjr@gmail.com> Co-authored-by: Sreenath Somarajapuram <somarajapuram@gmail.com> Co-authored-by: Omer Korner <omerkorner@gmail.com> Co-authored-by: joesavage-silabs <159480754+joesavage-silabs@users.noreply.github.com> Co-authored-by: Gregory L <gregory.linford@mistral.ai> Co-authored-by: David Soria Parra <167242713+dsp-ant@users.noreply.github.com> Co-authored-by: Moustapha Ebnou <155577789+mous222@users.noreply.github.com> Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com> Co-authored-by: Claude <noreply@anthropic.com> Co-authored-by: Jerome <jerome@anthropic.com> Co-authored-by: xavier <84836280+dragonier23@users.noreply.github.com> Co-authored-by: keurcien <keurcien.luu@gmail.com> Co-authored-by: Tim Esler <tim.esler@gmail.com> Co-authored-by: San Nguyen <22189661+sandangel@users.noreply.github.com> Co-authored-by: Justin Wang <89049861+justin-yi-wang@users.noreply.github.com> Co-authored-by: jess <jessachandler@gmail.com> Co-authored-by: Peter Alexander <pja@anthropic.com> Co-authored-by: Reid Geyer <12072650+reidg44@users.noreply.github.com> Co-authored-by: Eleftheria Stein-Kousathana <eleftheria.kousathana@gmail.com> Co-authored-by: Christian Clauss <cclauss@me.com> Co-authored-by: pchoudhury22 <pchoudhury22@apple.com> Co-authored-by: owengo <owengo@users.noreply.github.com> Co-authored-by: Olivier Schiavo <olivier.schiavo@wengo.com> Co-authored-by: Steve Billings <billings.steve@gmail.com> Co-authored-by: Mike Salvatore <mike.s.salvatore@gmail.com> Co-authored-by: pengwa <pengwa@microsoft.com> Co-authored-by: Your Name <youremail@yourdomain.com> Co-authored-by: Jon Shea <jonshea@jonshea.com> Co-authored-by: automaton82 <terrence.sheflin@gmail.com> Co-authored-by: Yukuan Jia <jiayukuan@huawei.com> Co-authored-by: Lorenzo <lorenzo_cesconeto@hotmail.com> Co-authored-by: ZhangChuanhui <57099533+zhangch-ss@users.noreply.github.com> Co-authored-by: zhangchuanhui <zhangchal@digitalchina.com> Co-authored-by: Marcus Shu <46469249+shulkx@users.noreply.github.com> Co-authored-by: Brandon Wu <49291449+brandonspark@users.noreply.github.com> Co-authored-by: Dogacan Colak <dogacancolak@gmail.com> Co-authored-by: AishwaryaKalloli <30429206+AishwaryaKalloli@users.noreply.github.com> Co-authored-by: lorenss-m <saeclmusic@gmail.com> Co-authored-by: Rocky Haotian Du <2712479005@qq.com> Co-authored-by: Fenn Bailey <fennb@users.noreply.github.com> Co-authored-by: daamitt <147169947+daamitt@users.noreply.github.com> Co-authored-by: Mat Leonard <137834585+mat-octave@users.noreply.github.com> Co-authored-by: Samuel Felipe Chenatti <samuel.chenatti@gmail.com> Co-authored-by: Brandon Shar <6599653+BrandonShar@users.noreply.github.com> Co-authored-by: mingo007 <maoqiming1@huawei.com> Co-authored-by: adam jones <domdomegg+git@gmail.com> Co-authored-by: Yann Jouanin <yann.jouanin@valueandco.com> Co-authored-by: Koichi ITO <koic.ito@gmail.com> Co-authored-by: Cole Murray <colemurray.cs@gmail.com> Co-authored-by: inaku <63503085+inaku-Gyan@users.noreply.github.com> Co-authored-by: Chris Coutinho <12901868+cbcoutinho@users.noreply.github.com> Co-authored-by: Paul Carleton <paulc@anthropic.com> Co-authored-by: Camila Rondinini <camila@anthropic.com> Co-authored-by: Victorien <65306057+Viicos@users.noreply.github.com> Co-authored-by: Andrii Blyzniuk <bliznyuk.andrey@gmail.com> Co-authored-by: Liang Wu <18244712+wuliang229@users.noreply.github.com> Co-authored-by: adam jones <adamj+git@anthropic.com> Co-authored-by: Olivier Chafik <ochafik@anthropic.com> Co-authored-by: Tyler Mailman <themailmaninbox@gmail.com> Co-authored-by: TheMailmans <tyler@example.com> Co-authored-by: Edison <Edison.A.N@hotmail.com>

* Add regression test for stateless request memory cleanup (modelcontextprotocol#1140) * Implement RFC9728 - Support WWW-Authenticate header by MCP client (modelcontextprotocol#1071) * Add streamable HTTP starlette example to Python SDK docs (modelcontextprotocol#1111) * fix markdown error in README in main (modelcontextprotocol#1147) * README - replace code snippets with examples - add lowlevel to snippets (modelcontextprotocol#1150) * README - replace code snippets with examples - streamable http (modelcontextprotocol#1155) * chore: don't allow users to create issues outside the templates (modelcontextprotocol#1163) * Tests(cli): Add coverage for helper functions (modelcontextprotocol#635) * Docs: Update CallToolResult parsing in README (modelcontextprotocol#812) Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> * docs: add pre-commit install guide on CONTRIBUTING.md (modelcontextprotocol#995) Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> * fix flaky fix-test_streamablehttp_client_resumption test (modelcontextprotocol#1166) * README - replace code snippets with examples -- auth examples (modelcontextprotocol#1164) * Support falling back to OIDC metadata for auth (modelcontextprotocol#1061) * Add CODEOWNERS file for sdk (modelcontextprotocol#1169) * fix flaky test test_88_random_error (modelcontextprotocol#1171) * Make sure `RequestId` is not coerced as `int` (modelcontextprotocol#1178) * Fix: Replace threading.Lock with anyio.Lock for Ray deployment compatibility (modelcontextprotocol#1151) * fix: fix OAuth flow request object handling (modelcontextprotocol#1174) * update codeowners group (modelcontextprotocol#1191) * fix: perform auth server metadata discovery fallbacks on any 4xx (modelcontextprotocol#1193) * server: skip duplicate response on CancelledError (modelcontextprotocol#1153) Co-authored-by: ihrpr <inna@anthropic.com> * Unpack settings in FastMCP (modelcontextprotocol#1198) * chore: Remove unused prompt_manager.py file (modelcontextprotocol#1229) Co-authored-by: Tapan Chugh <tapanc@cs.washington.edu> * Improved supported for ProtectedResourceMetadata (modelcontextprotocol#1235) Co-authored-by: Paul Carleton <paulcarletonjr@gmail.com> * chore: Remove unused variable notification_options (modelcontextprotocol#1238) * Improve README around the Context object (modelcontextprotocol#1203) * fix: allow to pass `list[str]` to `token_endpoint_auth_signing_alg_values_supported` (modelcontextprotocol#1226) * Remove strict validation on `response_modes_supported` member of `OAuthMetadata` (modelcontextprotocol#1243) * Add pyright strict mode on the whole project (modelcontextprotocol#1254) * Consistent casing for default headers Accept and Content-Type (modelcontextprotocol#1263) * Update dependencies and fix type issues (modelcontextprotocol#1268) Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com> * fix: prevent async generator cleanup errors in StreamableHTTP transport (modelcontextprotocol#1271) Co-authored-by: David Soria Parra <167242713+dsp-ant@users.noreply.github.com> * chore: uncomment .idea/ in .gitignore (modelcontextprotocol#1287) Co-authored-by: Claude <noreply@anthropic.com> * docs: clarify streamable_http_path configuration when mounting servers (modelcontextprotocol#1172) * feat: Add CORS configuration for browser-based MCP clients (modelcontextprotocol#1059) Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com> Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> * Added Audio to FastMCP (modelcontextprotocol#1130) * fix: avoid uncessary retries in OAuth authenticated requests (modelcontextprotocol#1206) Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> * Add PATHEXT to default STDIO env vars in windows (modelcontextprotocol#1256) * fix: error too many values to unpack (expected 2) (modelcontextprotocol#1279) Signed-off-by: San Nguyen <vinhsannguyen91@gmail.com> Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * SDK Parity: Avoid Parsing Server Response for non-JsonRPCMessage Requests (modelcontextprotocol#1290) * types: Setting default value for method: Literal (modelcontextprotocol#1292) * changes structured temperature to not deadly (modelcontextprotocol#1328) * Update simple-resource example to use non-deprecated read_resource return type (modelcontextprotocol#1331) Co-authored-by: Claude <noreply@anthropic.com> * docs: Update README to include link to API docs for modelcontextprotocol#1329 (modelcontextprotocol#1330) * Allow ping requests before initialization (modelcontextprotocol#1312) * Python lint: Ruff rules for pylint and code complexity (modelcontextprotocol#525) * Fix context injection for resources and prompts (modelcontextprotocol#1336) * fix(fastmcp): propagate mimeType in resource template list (modelcontextprotocol#1186) Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * fix: allow elicitations accepted without content (modelcontextprotocol#1285) Co-authored-by: Olivier Schiavo <olivier.schiavo@wengo.com> * Use --frozen in pre-commit config (modelcontextprotocol#1375) * Return HTTP 403 for invalid Origin headers (modelcontextprotocol#1353) * Add test for ProtectedResourceMetadataParsing (modelcontextprotocol#1236) Co-authored-by: Paul Carleton <paulcarletonjr@gmail.com> Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * Fastmcp logging progress example (modelcontextprotocol#1270) Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * feat: add paginated list decorators for prompts, resources, and tools (modelcontextprotocol#1286) Co-authored-by: Claude <noreply@anthropic.com> * Remove "unconditionally" from conditional description (modelcontextprotocol#1289) * Use streamable-http consistently in examples (modelcontextprotocol#1389) * feat: Add SDK support for SEP-1034 default values in elicitation schemas (modelcontextprotocol#1337) Co-authored-by: Tapan Chugh <tapanc@cs.washington.edu> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * Implementation of SEP 973 - Additional metadata + icons support (modelcontextprotocol#1357) * Add error log for client stdio (modelcontextprotocol#924) Co-authored-by: Your Name <youremail@yourdomain.com> Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * Accept additional response_types values from OAuth servers (modelcontextprotocol#1323) * Issue 1379 patch - Fix MCP server OAuth not working with Visual Studio Code and others with extra grant_types (modelcontextprotocol#1380) * Add comprehensive Unicode tests for streamable HTTP transport (modelcontextprotocol#1381) * Update Icon.sizes to use string array format (modelcontextprotocol#1411) * Delete CODEOWNERS to eliminate notification overload (modelcontextprotocol#1413) * fix: fix the system message in simple-chatbot example (modelcontextprotocol#1394) * fix: improve misleading warning for progress callback exceptions (modelcontextprotocol#775) * fix: catch and rethrow SSEError during SSE connection establishment (modelcontextprotocol#975) Co-authored-by: zhangchuanhui <zhangchal@digitalchina.com> Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> * Add icons support for ResourceTemplate (modelcontextprotocol#1412) * Add documentation structure (modelcontextprotocol#1425) * Add documentation about testing (modelcontextprotocol#1426) * Improve OAuth protected resource metadata URL construction per RFC 9728 (modelcontextprotocol#1407) * feat: add ability to remove tools (modelcontextprotocol#1322) Co-authored-by: David Soria Parra <167242713+dsp-ant@users.noreply.github.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com> Co-authored-by: Claude <noreply@anthropic.com> * Update README to link to Python SDK documentation (modelcontextprotocol#1430) * fix: update CLAUDE.md to remove auto-addition of reviewers. (modelcontextprotocol#1431) * [client] Implement MCP OAuth scope selection and step-up authorization (modelcontextprotocol#1324) * Handles message type Exception in lowlevel/server.py _handle_message function. Mentioned as TODO on line 528. (modelcontextprotocol#786) Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * Fix workspace configuration error with structured_output_lowlevel.py (modelcontextprotocol#1471) Co-authored-by: lorenss-m <saeclmusic@gmail.com> * fix: Remove unnecessary constructor from ResourceServerSettings (modelcontextprotocol#1424) Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * feat: add resource annotations support to FastMCP (modelcontextprotocol#1468) * fix: send params as empty object for list methods without cursor (modelcontextprotocol#1453) * fix: Set the Server session initialization state immediately after respond… (modelcontextprotocol#1478) Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com> * feat: add tool metadata in FastMCP.tool decorator (modelcontextprotocol#1463) Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com> * Make client examples workspaces to reflect package code (modelcontextprotocol#1466) * Expose RequestParams._meta in ClientSession.call_tool (modelcontextprotocol#1231) Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * Allow CallToolResult to be returned directly to support _meta field for OpenAI Apps (modelcontextprotocol#1459) Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com> * fix: uv CVE-2025-62518 astral-tokio-tar issue GHSA-j5gw-2vrg-8fgx (modelcontextprotocol#1505) * fix: use proper dependency resolution in CI (modelcontextprotocol#1507) * Upgrade GitHub Actions (modelcontextprotocol#1473) * test: use errno.ENOENT for command not found assertion (modelcontextprotocol#1498) * Replace deprecated dev-dependencies with dependency-groups (modelcontextprotocol#1488) Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * update uv to 0.9.5 (modelcontextprotocol#1510) * Relax Accept header requirement for JSON-only responses (modelcontextprotocol#1500) * fix: replace deprecated dev-dependencies in examples/clients (modelcontextprotocol#1518) * fix: Update spec links to new modelcontextprotocol.io location (modelcontextprotocol#1491) * fix: Replace fixed sleep with active server readiness check in SSE tests (modelcontextprotocol#1526) * fix: Replace arbitrary sleeps with active server readiness checks in tests (modelcontextprotocol#1527) Co-authored-by: Claude <noreply@anthropic.com> * Fix flaky timeout test in test_88_random_error (modelcontextprotocol#1525) * fix: Replace remaining manual server polling with wait_for_server helper (modelcontextprotocol#1529) * Implement RFC 7523 JWT flows (modelcontextprotocol#1247) Co-authored-by: Yann Jouanin <yann.jouanin@valueandco.com> * Fix pyright error and replace wildcard import with explicit imports (modelcontextprotocol#1532) * Fix auth client example URL handling for oauth provider (modelcontextprotocol#1549) * docs: use article "an" before "MCP" instead of "a" (modelcontextprotocol#1558) * Update Starlette to 0.49.1 in uv.lock (modelcontextprotocol#1559) * Fix typo in `ClientSessionGroup` doc string (modelcontextprotocol#1572) * Implement SEP-985: OAuth Protected Resource Metadata discovery fallback (modelcontextprotocol#1548) Co-authored-by: Claude <noreply@anthropic.com> Co-authored-by: Paul Carleton <paulc@anthropic.com> * Add --frozen flag to uv run commands in Claude config (modelcontextprotocol#1583) * Add get_server_capabilities() to ClientSession (modelcontextprotocol#1588) * Add everything-server for comprehensive MCP conformance testing (modelcontextprotocol#1587) * Get baseline 100% clean coverage (modelcontextprotocol#1553) * Add end-of-file-fixer pre-commit hook (modelcontextprotocol#1610) * Add coverage baseline commit to git-blame-ignore (modelcontextprotocol#1613) * Add SEP-1034 conformance test support to everything-server (modelcontextprotocol#1604) Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com> * refactor: extract OAuth helper functions and simplify provider state (modelcontextprotocol#1586) * Add client_id_metadata_document_supported to OAuthMetadata (modelcontextprotocol#1603) * Fix OAuth discovery fallback and URL ordering (modelcontextprotocol#1624) * Refactor `func_metadata()` implementation (modelcontextprotocol#1496) * Fix CI highest resolution test to actually test highest versions (modelcontextprotocol#1609) * feat: Pass through and expose additional parameters in `ClientSessionGroup.call_tool` and `.connect_to_server` (modelcontextprotocol#1576) * fix get_client_metadata_scopes on 401 (modelcontextprotocol#1631) Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com> * chore: Lazy import `jsonschema` library (modelcontextprotocol#1596) Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com> * docs: Update examples to use stateless HTTP with JSON responses (modelcontextprotocol#1499) * Add tests for JSON Schema 2020-12 field preservation (SEP-1613) (modelcontextprotocol#1649) * Add client_secret_basic authentication support (modelcontextprotocol#1334) Co-authored-by: Paul Carleton <paulc@anthropic.com> * Implement SEP-1577 - Sampling With Tools (modelcontextprotocol#1594) Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> Co-authored-by: Claude <noreply@anthropic.com> * SEP-1330: Elicitation Enum Schema Improvements and Standards Compliance (modelcontextprotocol#1246) Co-authored-by: Tapan Chugh <tapanc@cs.washington.edu> Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * [auth][conformance] add conformance auth client (modelcontextprotocol#1640) Co-authored-by: Claude <noreply@anthropic.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * Implement SEP-986: Tool name validation (modelcontextprotocol#1655) * fix: url for spec (modelcontextprotocol#1659) * feat: implement SEP-991 URL-based client ID (CIMD) support (modelcontextprotocol#1652) Co-authored-by: Claude <noreply@anthropic.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * Update doc string on custom_route (modelcontextprotocol#1660) * Implement SEP-1036: URL mode elicitation for secure out-of-band interactions (modelcontextprotocol#1580) Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> * Skip empty SSE data to avoid parsing errors (modelcontextprotocol#1670) * SEP-1686: Tasks (modelcontextprotocol#1645) * Add on_session_created callback option (modelcontextprotocol#1710) * Add SSE polling support (SEP-1699) (modelcontextprotocol#1654) * Support client_credentials flow with JWT and Basic auth (modelcontextprotocol#1663) Co-authored-by: Claude <noreply@anthropic.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> * feat: backwards-compatible create_message overloads for SEP-1577 (modelcontextprotocol#1713) * Merge commit from fork * Auto-enable DNS rebinding protection for localhost servers When a FastMCP server is created with host="127.0.0.1" or "localhost" and no explicit transport_security is provided, automatically enable DNS rebinding protection. Both 127.0.0.1 and localhost are allowed as valid hosts/origins since clients may use either to connect. * Add tests for auto DNS rebinding protection on localhost Tests verify that: - Protection auto-enables for host=127.0.0.1 - Protection auto-enables for host=localhost - Both 127.0.0.1 and localhost are in allowed hosts/origins - Protection does NOT auto-enable for other hosts (e.g., 0.0.0.0) - Explicit transport_security settings are not overridden * Add IPv6 localhost (::1) support for DNS rebinding protection Extend auto-enable DNS rebinding protection to also cover IPv6 localhost. When host="::1", protection is now auto-enabled with appropriate allowed hosts ([::1]:*) and origins (http://[::1]:*). * Fix import ordering in test file * chore: update LATEST_PROTOCOL_VERSION to 2025-11-25 (modelcontextprotocol#1715) * fix: add lifespan context manager to StreamableHTTP mounting examples (modelcontextprotocol#1669) Co-authored-by: TheMailmans <tyler@example.com> Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com> * fix: handle ClosedResourceError in StreamableHTTP message router (modelcontextprotocol#1384) Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com> Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com> * fix: skip priming events and close_sse_stream for old protocol versions (modelcontextprotocol#1719) * refactor(auth): remove unused _register_client method (modelcontextprotocol#1748) * [MCP-266] Add tests for Gumloop server extensions * Fix uv workspace config for gumloop-mcp package name * Sync with upstream MCP SDK and fix merge conflicts * Fix tool cache timing and missing properties check in server.py * Fix coverage and add proper type annotations for Gumloop extensions * Version up * Skip README code example tests (Gumloop README has no code snippets) * Support gumloop and mcp outptuschema * Add publish tools to dev dependencies and update README for uv --------- Signed-off-by: San Nguyen <vinhsannguyen91@gmail.com> Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com> Co-authored-by: yurikunash <143175350+yurikunash@users.noreply.github.com> Co-authored-by: Pamela Fox <pamela.fox@gmail.com> Co-authored-by: Inna Harper <inna.hrpr@gmail.com> Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com> Co-authored-by: Ian Davenport <49379192+davenpi@users.noreply.github.com> Co-authored-by: Dagang Wei <functicons@gmail.com> Co-authored-by: Felix Weinberger <fweinberger@anthropic.com> Co-authored-by: Stanley Law <stanleylkal@gmail.com> Co-authored-by: Luca Chang <131398524+LucaButBoring@users.noreply.github.com> Co-authored-by: leweng <leweng@nvidia.com> Co-authored-by: Clare Liguori <liguori@amazon.com> Co-authored-by: lukacf <luka@peltarion.com> Co-authored-by: ihrpr <inna@anthropic.com> Co-authored-by: Tapan Chugh <chugh.tapan@gmail.com> Co-authored-by: Tapan Chugh <tapanc@cs.washington.edu> Co-authored-by: Yann Jouanin <4557670+yannj-fr@users.noreply.github.com> Co-authored-by: Paul Carleton <paulcarletonjr@gmail.com> Co-authored-by: Sreenath Somarajapuram <somarajapuram@gmail.com> Co-authored-by: Omer Korner <omerkorner@gmail.com> Co-authored-by: joesavage-silabs <159480754+joesavage-silabs@users.noreply.github.com> Co-authored-by: Gregory L <gregory.linford@mistral.ai> Co-authored-by: David Soria Parra <167242713+dsp-ant@users.noreply.github.com> Co-authored-by: Moustapha Ebnou <155577789+mous222@users.noreply.github.com> Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com> Co-authored-by: Claude 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felixweinberger marked this pull request as draft October 9, 2025 14:17

felixweinberger marked this pull request as ready for review October 9, 2025 14:23

felixweinberger requested review from Kludex and maxisbey October 9, 2025 14:23

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felixweinberger added the improves sdk consistency Improves consistency with other SDKs such as Tyepscript label Oct 9, 2025

felixweinberger marked this pull request as draft October 9, 2025 15:13

felixweinberger added 3 commits October 9, 2025 17:57

felixweinberger dismissed stale reviews from maxisbey and Kludex via a98c4f7 October 9, 2025 17:08

felixweinberger marked this pull request as ready for review October 9, 2025 17:11

felixweinberger commented Oct 9, 2025

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src/mcp/client/session.py Outdated Show resolved Hide resolved

felixweinberger requested review from Kludex, maxisbey and pja-ant October 9, 2025 17:39

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felixweinberger requested a review from maxisbey October 13, 2025 16:33

felixweinberger force-pushed the fweinberger/validation-consistency branch from daca273 to 9aa6cfd Compare October 13, 2025 16:45

felixweinberger force-pushed the fweinberger/validation-consistency branch from 9aa6cfd to 3217282 Compare October 13, 2025 16:46

fix: flip order of @overload & @deprecated to match docs

d4b0608

See: https://docs.python.org/3.13/library/warnings.html#warnings.deprecated @deprecated combined with @overload is specifically called out to be placed _after_ the @overload.

fix: improve deprecation warning string

28c6f0d

maxisbey previously approved these changes Oct 13, 2025

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felixweinberger and others added 2 commits October 14, 2025 10:57

Merge branch 'main' into fweinberger/validation-consistency

6daf63b

fix: remove unnecessary lint ignore

ee989cf

felixweinberger dismissed maxisbey’s stale review via ee989cf October 14, 2025 10:04

Merge branch 'main' into fweinberger/validation-consistency

1827420

felixweinberger requested a review from maxisbey October 14, 2025 10:08

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felixweinberger merged commit de89457 into main Oct 14, 2025
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felixweinberger deleted the fweinberger/validation-consistency branch October 14, 2025 10:11

0Delta pushed a commit to 0Delta/python-sdk that referenced this pull request Nov 27, 2025

fix: send params as empty object for list methods without cursor (mod…

43b583b

…elcontextprotocol#1453)

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fix: send params as empty object for list methods without cursor #1453

fix: send params as empty object for list methods without cursor #1453

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felixweinberger commented Oct 9, 2025 •

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fix: send params as empty object for list methods without cursor #1453

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