fastmcp/docs/patterns
Jeremiah Lowin 07d89c4038
Add transform system for modifying components in provider chains (#2836)
* Consolidate tool transformation logic into TransformingProvider

Tool transformations were previously scattered across LocalProvider,
ProxyProvider, and MCPConfig. This consolidates all transformation
logic into TransformingProvider via with_transforms(tool_transforms={...}).

- Add tool_transforms parameter to TransformingProvider
- Add tool_transforms to Provider.with_transforms()
- Remove transformation storage from LocalProvider and ProxyProvider
- Remove add_tool_transformation() and remove_tool_transformation() from FastMCP
- Add tool_transforms parameter to factory methods (from_openapi, from_fastapi, create_proxy)
- Update tests to use new patterns

* Fix: reject tool lookups by pre-transform name

* Add collision validation for tool_transforms and fix docstring examples

- Validate duplicate target names in tool_transforms raise ValueError
- Fix docstring examples to use arguments/ArgTransformConfig (not args/ArgTransform)
- Add test for collision validation

* Add server-level tool transform APIs and fix task registration

- Add AggregateProvider to present multiple providers as one
- Add _get_root_provider() to apply server-level transforms uniformly
- Fix _docket_lifespan to use root provider (ensures renamed tools
  register with correct keys for background execution)
- Add tool_transforms kwarg to __init__ (non-deprecated)
- Add add_tool_transform(), remove_tool_transform(), tool_transforms property
- Deprecate old API names (tool_transformations, add_tool_transformation, etc.)
- Update tests to use new API

* Add graceful degradation for provider errors in AggregateProvider

* Match original behavior: parallel queries with DEBUG logging

* Refactor transforms to middleware-style call_next pattern

Replaces the ad-hoc transformation system with a unified Transform
abstraction using the same call_next pattern as server middleware.

Key changes:
- New src/fastmcp/server/transforms/ module with Transform base class
- Namespace, ToolTransform, Visibility all implement the same interface
- Transforms compose via functools.partial chain building
- Visibility is now just the first transform in provider._transforms
- Server-level transforms apply after provider aggregation
- Task registration now applies full transform chain

Removes TransformingProvider, _BoundTransform, ComponentSource protocol.
User-facing API unchanged: mount(), add_transform(), enable/disable all
work as before.

* Add comprehensive transforms and visibility documentation

New docs/servers/providers/transforms.mdx covering:
- Mental model for middleware-style transform pattern
- Built-in transforms (Namespace, ToolTransform)
- Server vs provider-level transforms and ordering
- Tool modification (immediate vs deferred)
- Custom transform creation

New docs/servers/visibility.mdx covering:
- Enable/disable API for runtime visibility control
- Keys and tags for targeting components
- Allowlist mode with only=True
- Server vs provider visibility layering

Updates existing docs to reference new pages and simplifies
redundant content. Visibility is documented as a user feature,
not as an implementation detail.

* Restructure transforms docs and delete tool-transformation pattern

* Cleanup: simplify get_tasks and remove unused Provider.get_component

* Update loq

* Update loq limits and add loq note to AGENTS.md

* Deprecate add_tool_transformation and tool_transformations param

* Address PR review feedback: remove redundant imports, fix path reference

* Add missing imports to code examples in v3-features.mdx
2026-01-12 22:11:16 -05:00
..
cli.mdx Add --reload flag for auto-restart on file changes (#2816) 2026-01-09 08:44:27 -05:00
contrib.mdx Add MCP json output from CLI (#1056) 2025-07-06 10:23:50 -04:00
testing.mdx docs: clarify pytest-asyncio dependency and asyncio mode configuration (#2399) 2025-11-15 10:34:29 -05:00