Refactor and API Redesign

[shahar4499]

Complete API Redesign

This PR introduces a complete refactor of the FastAPI-MCP API.

We changed the approach from relying on FastMCP, to wrapping the lower-level server, which inherently fixes a lot of the problems and limitations we had in the library.

What's Changed

New Class-Based API

• Replaced the function-based API with a new FastApiMCP class for better usability, and for laying the ground for extension and composability
• Explicit separation between MCP instance creation and mounting with mcp = FastApiMCP(app) followed by mcp.mount()

Breaking Changes

• Removed function-based API (add_mcp_server, create_mcp_server, etc.)
• Removed custom tool support via @mcp.tool() decorator. This is inherent to not using FastMCP anymore, which is what provided this feature. If the community needs a way to add custom MCP tools alongside the existing API, we will provide a way to do so.
• Updated minimum MCP dependency to v1.6.0

FastAPI-Native Approach for Transport

Thanks @johschmidt42 ! This fixes #28

• Flexible routing options for placing your MCP server on any FastAPI app or APIRouter
• A stabler transport using a FastAPI-native approach instead of mounting a whole ASGI app

Enhanced Deployment Options

• Added support for deploying MCP servers separately from your API service

Bug Fixes and Improved Code Quality

• Fixed numerous bugs in OpenAPI schema to tool conversion. Addresses issues like:
  • [BUG] #40
  • [BUG] Error when calling MCP server without optional fields #45
  • and several more issues raised in the Slack community
• Refactored codebase for improved maintainability
• Added support for "refreshing" with setup_server() when dynamically adding FastAPI routes after instantiating FastApiMCP.
  • Fixes When endpoints are declared after calling add_mcp_server, they are not registered by the MCP server #19

Testing

• Added a more comprehensive test suite
• Increased test coverage to 92%

Examples

See the new examples directory for:

• Simple integration with a single app
• Separate deployment of API and MCP servers
• Full schema description options
• Adding endpoints after MCP server creation

[codecov]

Codecov Report

Attention: Patch coverage is 92.19360% with 100 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
fastapi_mcp/transport/sse.py	22.03%	46 Missing ⚠️
fastapi_mcp/server.py	84.67%	19 Missing ⚠️
fastapi_mcp/openapi/convert.py	90.44%	13 Missing ⚠️
tests/test_openapi_conversion.py	91.66%	13 Missing ⚠️
fastapi_mcp/openapi/utils.py	93.67%	5 Missing ⚠️
fastapi_mcp/utils/testing.py	92.30%	2 Missing ⚠️
tests/fixtures/example_data.py	93.54%	2 Missing ⚠️

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