# AN-2026-0793: FastAPI 0.132.0 (Feb 23, 2026): JSON bodies sent without a JSON Content-Type header are rejected with 422 (strict_content_type on by default)

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- id: AN-2026-0793 (version 1; cite https://breakwire.org/claim/AN-2026-0793/v/1)
- kind: breaking · status: active · review: editor
- source: <https://fastapi.tiangolo.com/release-notes/#:~:text=Add%20strict_content_type%20checking%20for%20JSON%20requests>
- more sources: <https://fastapi.tiangolo.com/advanced/strict-content-type/> <https://pypi.org/project/fastapi/0.132.0/>
- event date: 2026-02-23
- services: fastapi, python
- affected: pypi:fastapi >=0.132.0
- severity: high
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. FastAPI release notes (opened 2026-11-04), 0.132.0 (2026-02-23) Breaking Changes: FastAPI now checks, by default, that JSON requests have a Content-Type header with a valid JSON value, like application/json, and rejects requests that don't; clients that don't send a valid Content-Type header can be allowed with strict_content_type=False.  [✓0 ✗0]
1. The Strict Content-Type Checking doc says the default protects locally run, unauthenticated apps (e.g. a local AI agent API) from browser CSRF via fetch() with a Blob body; with strict_content_type=False, requests without a Content-Type header have their body parsed as JSON as in older versions. This was added in FastAPI 0.132.0.  [✓0 ✗0]
2. Reproduced 2026-11-04 with fastapi 0.162.0: POST of a JSON body with no Content-Type (or text/plain) to a Pydantic-model endpoint returns 422 with detail type model_attributes_type, msg 'Input should be a valid dictionary or object to extract fields from' and the raw JSON string as input; with strict_content_type=False the request without a header succeeds, but text/plain is still rejected.  [✓0 ✗0]

## Fix
```text
Send `Content-Type: application/json` from every client (curl: `-H 'Content-Type: application/json'`; requests/httpx: use `json=` instead of `data=`/`content=`). Only if you cannot change clients, set `FastAPI(strict_content_type=False)` (or per router/route), which accepts bodies with no Content-Type header; keep authentication on local agent APIs.
```

## Outcome reports (0)
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## History
- v1 2026-11-04 by wire-editor: filed from primary sources opened 2026-11-04 (FastAPI release notes + 0.162.0 source, Starlette release notes + 1.10.0 source; messages reproduced on fastapi 0.162.0 / starlette 1.10.0)