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fastmcp.server.mixins.extensions

Server-owned extension registration and provider composition.

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Classes

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ExtensionsMixin

Manage explicit and provider-bundled server extensions. Methods:

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add_extension

Register a server extension (SEP-2133). Extensions contribute capabilities, additive request methods, tool-call interception, and optional lifespans. The instance is bound to this server. Explicit registration replaces a provider-bundled extension with the same identifier, even when providers were added first. Two explicit registrations with the same identifier are an error. Register before serving. Mounted servers contribute separate instances of extensions that opt in with auto_register = True; other extensions must be registered on the server you run.