fix: change Resource URI fields from AnyUrl to str #1865
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Github-Issue: #1574
The Python SDK was incorrectly using Pydantic's AnyUrl for URI fields on resource types. This rejected relative paths like 'users/me' that are valid according to the MCP specification, which defines URIs as plain strings without format validation. This change updates the following types to use str instead of AnyUrl: - Resource.uri - ReadResourceRequestParams.uri - ResourceContents.uri - SubscribeRequestParams.uri - UnsubscribeRequestParams.uri - ResourceUpdatedNotificationParams.uri - FastMCP Resource.uri (base class) Client and server session methods now accept str | AnyUrl for backwards compatibility, converting to string internally. Updates migration.md with documentation of this breaking change. Github-Issue: #1574
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Summary
Change Resource URI fields from Pydantic's
AnyUrlto plainstrto match the MCP specification and TypeScript SDK behavior.Motivation and Context
The Python SDK was using
AnyUrlfor URI fields which rejected relative paths likeusers/methat are valid according to the MCP spec. The spec definesurias a plain string, and the TypeScript SDK usesz.string()with no validation.Fixes #1574
How Has This Been Tested?
tests/issues/test_1574_resource_uri_validation.pywith 9 test cases covering all affected typesAnyUrl()wrappersBreaking Changes
Minor - code that explicitly passes
AnyUrlobjects will still work (auto-converted to string). TheClientSessionmethods maintain backwards compatibility by accepting bothstrandAnyUrl.Types of changes
Checklist
Additional context
Affected types in
src/mcp/types.py:Resource.uriReadResourceRequestParams.uriResourceContents.uriSubscribeRequestParams.uriUnsubscribeRequestParams.uriResourceUpdatedNotificationParams.uriMigration guide added to
docs/migration.md.