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Advanced Features

FastRouter is designed for performance and developer experience. Here are some of the advanced features that set it apart.

Static Analysis (Tree-sitter)

FastRouter uses Static Analysis to discover your routes. Instead of importing every file in your routes/ directory at startup, it uses Tree-sitter to parse the source code and identify: - Which HTTP methods are implemented (get, post, etc.). - The function signatures (parameters, type hints, defaults). - Docstrings for OpenAPI documentation.

Why Static Analysis?

  • Speed: Startup is nearly instantaneous, even with hundreds of routes.
  • Safety: We don't execute any top-level code in your route files during discovery.
  • Validation: We can detect "stray" functions that don't match HTTP methods and warn you.

Lazy Loading

By default, FastRouter is Lazy. It doesn't import your route modules until the first request hits that specific endpoint.

Side-Effect Isolation

Because of lazy loading, any top-level code in your route files (like database connections or heavy model loading) won't run until it's actually needed.

Smart Fallback

If a route uses complex FastAPI features that require runtime introspection (like Depends(), Body(), or custom Pydantic models), FastRouter automatically detects this and falls back to Immediate Loading for that specific route to ensure full compatibility.

Rich OpenAPI Metadata

FastRouter automatically enhances your Swagger UI (/docs) using your Python docstrings.

Summaries & Descriptions

  • Summary: The first line of your function docstring.
  • Description: Everything after the first line.
def get(id: int):
    """
    Get a user by their ID.

    This part will appear in the expanded description section.
    You can use **Markdown** here!
    """
    return {"id": id}

Tag Metadata

You can customize the documentation for entire directories (tags) using set_tag_metadata:

from fast_router import fast_router

router = fast_router("routes")
router.set_tag_metadata(
    "users", 
    description="Operations with users and their profiles.",
    external_docs={"description": "User Guide", "url": "https://example.com/docs"}
)

Parameter Validation

FastRouter validates your dynamic segment names. If you use a parameter in a filename (like [id].py) but forget to include it in your function signature (def get():), FastRouter will raise a clear error at startup.