Unprocessable Content

4xx Client Error

ELI5

Your request looks right, but the data doesn't make sense according to our business rules. Fix the data and try again.

Use 422 when the request is well-formed and understood, but its instructions or values are semantically invalid.

•Return 422 for validation failures, domain-rule violations, and semantically invalid content
•Use it when the client can fix the submitted content without changing the target resource state
•Validation errors on request data
•Business rule violations
•Invalid field values (e.g., negative age)
•Failed schema validation
•Semantic errors in well-formed requests

•No status-specific header is required; still send normal HTTP metadata such as Content-Type, caching, or tracing headers when they help the client.

•Include actionable validation details such as field names, rule failures, or machine-readable error codes

•Use 400 when the request could not be parsed or understood structurally
•Use 409 when the problem is a conflict with current server state rather than bad submitted content
•Syntax errors (use 400 Bad Request)
•State conflicts (use 409 Conflict)
•Authentication issues (use 401 Unauthorized)

Request:

POST https://api.example.test/api/users

# Body
{
  "age": -5
}

Response:

422 Unprocessable Content

# Headers
Content-Type: application/json

# Body
{
  "error": "unprocessable_content"
}

Age cannot be negative, violates business rules

There's a conflict - what you're trying to do clashes with something that already exists or the current state.

Your request doesn't make sense or has mistakes in it. Check what you're sending and try again.