[FAQ Bot] NEW: Why does http://localhost:8000 return { "detail": "Not Found" } afte

_questions/ai-dev-tools-zoomcamp/02-development/003_b7cb4e67d0_fastapi-root-404-not-found.md

@@ -0,0 +1,26 @@
+---
+id: b7cb4e67d0
+question: 'Why does `http://localhost:8000` return `{ "detail": "Not Found" }` after
+  starting my FastAPI backend?'
+sort_order: 3
+---
+
+When you start a FastAPI server, FastAPI will only respond to routes you explicitly define. The `{"detail":"Not Found"}` response means your app has no endpoint registered for the root path (`/`), so FastAPI returns a `404`.
+
+To confirm the server is up, use the built-in docs or an existing endpoint:
+- `http://localhost:8000/docs`
+- `http://localhost:8000/<your_defined_route>`
+
+If you want `http://localhost:8000/` to return something, add a root route:
+
+```python
+from fastapi import FastAPI
+
+app = FastAPI()
+
+@app.get("/")
+def health_check():
+    return {"message": "API is running"}
+```
+
+Common cause: you’re hitting `/` but your main routes are under a prefix (e.g. `/v1/...`), or you haven’t added any `@app.get("/")` handler yet.