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fix: add explicit type annotation for call_tool decorator #1826

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Merged
Kludex merged 3 commits into from
Jan 6, 2026
Merged

fix: add explicit type annotation for call_tool decorator #1826

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4f2942e
fix: add explicit type annotation for call_tool decorator
Jan 4, 2026
da2ddd2
type inline
Kludex Jan 6, 2026
e18da92
Merge branch 'main' into fix/1822-decorator-paramspec
Kludex Jan 6, 2026
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21 changes: 9 additions & 12 deletions src/mcp/server/lowlevel/server.py
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Original file line number Diff line number Diff line change
Expand Up @@ -105,6 +105,14 @@ async def main():
UnstructuredContent: TypeAlias = Iterable[types.ContentBlock]
CombinationContent: TypeAlias = tuple[UnstructuredContent, StructuredContent]

# type alias for call_tool handler function signature
CallToolHandler: TypeAlias = Callable[
[str, dict[str, Any]],
Awaitable[
UnstructuredContent | StructuredContent | CombinationContent | types.CallToolResult | types.CreateTaskResult
],
]

# This will be properly typed in each Server instance's context
request_ctx: contextvars.ContextVar[RequestContext[ServerSession, Any, Any]] = contextvars.ContextVar("request_ctx")

Expand Down Expand Up @@ -497,18 +505,7 @@ def call_tool(self, *, validate_input: bool = True):
If outputSchema is defined, validates structuredContent or errors if missing.
"""

def decorator(
func: Callable[
...,
Awaitable[
UnstructuredContent
| StructuredContent
| CombinationContent
| types.CallToolResult
| types.CreateTaskResult
],
],
):
def decorator(func: CallToolHandler) -> CallToolHandler:
logger.debug("Registering handler for CallToolRequest")

async def handler(req: types.CallToolRequest):
Expand Down