HTTP 422 Unprocessable Content (Unprocessable Entity)

HTTP 422 Unprocessable Content — The request is well-formed, but its contents fail validation.

Class

4xx Client Error

Defined in

RFC 9110 §15.5.21

Official

Yes (IANA registry)

Cacheable by default

No (unless Cache-Control/Expires say so)

Safe to retry

Not without changing the request

What does HTTP 422 mean?

422 Unprocessable Content (long known as "Unprocessable Entity", from WebDAV's RFC 4918) means the server understands the content type and the syntax is correct, but it can't process the contained instructions — in practice, the data fails validation.

It's the standard validation-error status in many frameworks: Ruby on Rails, Laravel, FastAPI and GitHub's API all return 422 for invalid input.

When is 422 used?

• A required field is empty or a value has the wrong format (email, date, phone).
• A value is out of range (quantity −1, a date in the past).
• References to related records that don't exist (categoryId: 999).
• FastAPI/Pydantic schema validation fails.

Common causes of a 422

• The form or JSON you sent is well-formed but has invalid values.
• Client and server disagree on the schema after an API change (renamed or newly required field).

How to fix 422 Unprocessable Content

If you're visiting the site

1. Read the error messages next to the form fields, correct the highlighted values and resubmit.

If you run the site or API (developers)

1. Return field-level details so clients can show them inline, e.g. RFC 9457 Problem Details with an errors array.
2. Use 400 for unparseable bodies and 422 for valid syntax with invalid values — and be consistent across your API.
3. In FastAPI, read the detail array: each item has loc, msg and type describing exactly which field failed.

Returning or handling 422: server examples

const User = z.object({ email: z.string().email(), age: z.number().int().min(13) });

app.post("/api/users", (req, res) => {
  const r = User.safeParse(req.body);
  if (!r.success) return res.status(422).json({ errors: r.error.issues });
  // ...
});

// app/api/example/route.ts (Next.js App Router)
export async function POST(req: Request) {
  const body = await req.json();
  if (!/^\S+@\S+$/.test(body.email ?? ""))
    return Response.json({ errors: [{ field: "email", message: "Enter a valid email" }] }, { status: 422 });
  // ...
}

# Pydantic validation failure → 422 with details:
# {"detail":[{"type":"missing","loc":["body","email"],"msg":"Field required"}]}

Example 422 response

HTTP/1.1 422 Unprocessable Content
Content-Type: application/problem+json

{"type":"https://example.com/validation","title":"Invalid input","status":422,
 "errors":[{"field":"email","message":"must be a valid email address"}]}

Related status codes

• 400 Bad RequestThe server can't process the request because it's malformed or invalid.
• 409 ConflictThe request conflicts with the current state of the resource.
• 415 Unsupported Media TypeThe server refuses the request because the body's format (Content-Type) isn't supported.

Related tools

• HTTP status codes — full list
• HTTP headers reference
• cURL converter
• Mock API — fake REST endpoints with custom status codes
• Webhook tester — inspect incoming requests