Home / HTTP errors / 400 Bad Request
HTTP error
400 Bad Request
The server could not understand the request.
What it means
The server received the request but refused to process it because something about the request itself is wrong. The problem is on the client side, so sending the same request again gives the same result.
Common causes
- A malformed URL, often with invalid characters or broken encoding
- Cookies that are too large or corrupted
- A request header that is too long or invalid
- A JSON or form body that does not match what the API expects
- An upload bigger than the server allows
How to fix it
If you are a visitor
- Check the address for typos and stray characters
- Clear the cookies for this site and reload the page
- Try a private window to rule out a browser extension
If you run the site
- Read the server or application log: it usually names the rejected field
- Check the header and cookie size limits of your web server and proxy
- Compare the request body with your API schema
Catch it before your users do
You can check the status code of any address right now. To hear about 400 errors as they happen, an HTTP(S) monitor requests the page around the clock, compares the response with the status codes you expect and alerts you when it does not match.
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