4xx Client error
422 Unprocessable Content
The request is well-formed but its content fails validation.
The JSON parses fine, but values break business rules — an invalid email, a negative quantity, an end date before the start date.
Common causes and fixes
- Read the error details in the body; frameworks such as FastAPI and Rails list each invalid field.
- Many APIs use 422 for validation errors and 400 for syntax errors.
Example response
HTTP/1.1 422 Unprocessable Content
Date: Thu, 22 Oct 2026 08:00:00 GMT Check a URL’s status with curl -I https://example.com, which prints the status line and headers.