Before getting into it, how Swagger UI gets generated, please have a look of project structure which I am using.
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Application Structure
Nobody wrote a Swagger page for this project. It’s assembled automatically by FastAPI from the exact same route objects you just walked through — routing metadata, response_model, tags, function signatures, docstrings. Here's the full mechanism.
Step 1 — Route registration happens first (at import time)
Every @router.get(...), @router.post(...) decorator in the codebase doesn't just register a URL — it builds a rich object called APIRoute and stores far more than "path → function."
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router used as an example
When this decorator runs, FastAPI captures:
The path: /stats (later becomes /api/v1/dashboard/stats once prefixes are applied)
The HTTP method: GET
The tag: "Dashboard" (from APIRouter(prefix="/dashboard", tags=["Dashboard"]))
The response schema: DashboardStats — and by extension, the schema of StatsBlock nested inside it
