HTTP status code

The HTTP 422 status code stands for "Unprocessable Entity". It is a client error response indicating that the server understands the request but cannot process the instructions because the request contains semantically erroneous data or is in an invalid format.

When is HTTP 422 Used?

• The 422 status code is typically used in situations where the request is well-formed, but the server is unable to process it due to validation errors or semantic problems with the data.
• It is often seen in APIs, especially in web applications where users submit data (such as form submissions or JSON payloads) that does not meet the required format or business rules.

Common Causes of HTTP 422 Errors

• Invalid data format: The server expects certain data types or formats, and the request contains incorrect data (e.g., submitting a string when a number is expected).
• Failed validation: The data in the request might not meet the validation criteria set by the server or application, such as missing required fields or providing data outside an allowed range.
• Semantic errors: The data may be logically incorrect or inconsistent, even if the syntax is valid (e.g., a date in the future when only past dates are allowed).
• Failed business rules: The data may violate business logic constraints, such as trying to create a duplicate entry when the system requires unique values.

Example Scenarios

• A client submits a registration form with an invalid email address format, causing the server to return a 422 error to indicate the invalid data.
• A user tries to update a database record with a date in the future, but the system only accepts past dates, resulting in a 422 error.
• A JSON payload sent to an API is missing a required field or contains a field with a value outside the acceptable range.

Example

Client Request (Invalid Data)

    
        POST /users HTTP/1.1
        Host: example.com
        Content-Type: application/json

        {
          "username": "john_doe",
          "email": "invalid-email",
          "birthdate": "1990-01-01"
        }
    

(The client tries to create a user, but the email is in an invalid format.)

Server Response (422 Unprocessable Entity)

    
        HTTP/1.1 422 Unprocessable Entity
        Content-Type: application/json

        {
          "error": "The provided email address is invalid. Please provide a valid email format."
        }
    

Best Practices for Handling HTTP 422

• Provide clear error messages: When returning a 422 response, include a detailed error message that explains what data is wrong and why it cannot be processed.
• Validate data thoroughly: Ensure that the data sent to the server is well-validated before accepting it. This includes checking for required fields, proper formatting, and adherence to business logic.
• Inform the user: If the error occurs due to invalid data provided by the client (e.g., a bad email address), make sure the user knows how to correct the issue so they can try again.
• Return specific error details: When possible, provide specific information about which fields caused the error, such as email: invalid format.

Summary

HTTP 422 is used when the server understands the request but cannot process it due to semantic errors or validation issues with the data. The client should check the data for errors in formatting, required fields, or logical consistency to resolve the issue. This status code is often used in APIs or web applications where user input is validated and must meet specific criteria.