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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Public API for runtime handler registration/deregistration on low-level Server","articleBody":"## Summary\n\nThe low-level `Server` class has a private `_add_request_handler()` method but no public API for adding or removing request/notification handlers at runtime. The only supported way to register handlers is via `on_*` constructor kwargs, which means all handlers must be known at construction time.\n\nThis is limiting for frameworks and advanced use cases that need to:\n- Register handlers for protocol extensions or custom methods after server construction\n- Remove or replace handlers dynamically (e.g., feature flags, hot-reloading, test fixtures)\n- Register notification handlers post-construction (currently no mutation API at all for `_notification_handlers`)\n\n### Current state\n\n- [`_add_request_handler()`](https://github.com/modelcontextprotocol/python-sdk/blob/0fe16dd5fddf/src/mcp/server/lowlevel/server.py#L237-L243) exists but is private. It silently replaces existing handlers.\n- [`_has_handler()`](https://github.com/modelcontextprotocol/python-sdk/blob/0fe16dd5fddf/src/mcp/server/lowlevel/server.py#L245-L247) is also private.\n- There is no remove/deregister method for either request or notification handlers.\n- `MCPServer.completion()` already uses `_add_request_handler()` with a `pyright: ignore[reportPrivateUsage]` suppression and a TODO acknowledging this needs a better pattern.\n\n### Proposal\n\nMake handler registration/deregistration a first-class public API on the low-level `Server`:\n\n```python\nserver.add_request_handler(method: str, handler: Callable) -\u003e None\nserver.remove_request_handler(method: str) -\u003e None\nserver.add_notification_handler(method: str, handler: Callable) -\u003e None\nserver.remove_notification_handler(method: str) -\u003e None\nserver.has_handler(method: str) -\u003e bool\n```\n\n### Related issues\n\n- #2105 — Custom method handlers on MCPServer (higher-level, different scope)\n- #1701 — Public API audit\n- #1233 — Middleware support (may interact with handler registration)\n\n\u003csub\u003e[AI Disclaimer](https://gist.github.com/maxisbey/6123d132484e4c533eab519a2800693d)\u003c/sub\u003e","author":{"url":"https://github.com/maxisbey","@type":"Person","name":"maxisbey"},"datePublished":"2026-02-24T13:50:17.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/2135/python-sdk/issues/2135"}