Mock 422 Unprocessable Entity Response

422 Unprocessable Entity

The 422 status code indicates that the server understands the content type and syntax of the request, but the data is semantically invalid. It is commonly used by frameworks like Laravel and Ruby on Rails for validation errors.

Response Structure

{
  "message": "The given data was invalid.",
  "errors": {
    "email": [
      "The email field is required.",
      "The email must be a valid email address."
    ],
    "password": [
      "The password must be at least 8 characters.",
      "The password must contain at least one uppercase letter."
    ],
    "age": [
      "The age must be a number.",
      "The age must be between 18 and 120."
    ]
  }
}

400 vs 422

Aspect	400 Bad Request	422 Unprocessable Entity
Syntax	Malformed JSON, wrong Content-Type	Valid JSON, correct syntax
Semantics	N/A (couldn't parse)	Fields present but values invalid
Common in	Express, Fastify	Laravel, Rails, Phoenix
RFC	HTTP/1.1	WebDAV (RFC 4918)

Field-Grouped Errors

This pattern groups errors by field name, with each field having an array of error messages. This is particularly useful for:

• Displaying multiple errors per field
• Programmatically highlighting all invalid fields
• Supporting internationalized error messages

Frontend Integration

Most form libraries (React Hook Form, Formik, VeeValidate) have built-in support for setting field-level errors. Map the response errors object directly to the form state:

Object.entries(response.errors).forEach(([field, messages]) => {
  setError(field, { message: messages[0] });
});