You send a request to an API with valid JSON and the correct headers. At first glance, everything seems fine. But instead of a successful response, the server returns an error message: 422 Unprocessable Entity.
This status code means that the server understands your request technically, but cannot process its content. The structure is correct, but the data does not meet the expected validation rules.
Why do you get a 422?
Because you are sending something that is not correct within the rules of the model or validation system.
It may be:
- You are missing a required field
- You enter a value that is not allowed (for example, a negative price)
- Or you are trying to modify something that is not valid in the current context
Frameworks such as Laravel, Rails or Django REST usually indicate exactly what is wrong. Not with a piece of text, but with structured error messages. You can do something with that.
What makes a 422 different from a 400?
A 400 Bad Request means that the request as a whole is not constructed correctly, think missing parentheses, incorrect headers, or invalid JSON.
In contrast, a 422 status code says: your request is technically valid, but content is not okay. Consider the difference between a misdirected letter and one that arrives cleanly but with wrong information in it.
Where do you come across this?
Especially with REST APIs that strictly validate at the field level. Think forms, user registration, product updates, and so on. It is also common in front-end apps that talk to a backend where not all client-side validation is enabled or working.
What can you do?
You don't need to open a debugging tool. Just look at what the server returns to you. If all goes well, you'll see exactly what fields are missing or why a value was rejected.
So:
- Start at the error message itself
- Check your payload (field names, types, mandatory attributes)
- Check the API documentation (or talk to the dev who built it)
And above all, don't get stuck in "but it's valid JSON, right?". That's not the point. The point is what you're trying to do with it.
Summary
The 422 status code is not a crash, not an error in your build. It's the server saying: this is not correct according to my rules. That can be frustrating, especially when everything looks neat on the outside, but it's exactly the kind of error message that helps you build better.
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