Client Error

HTTP 400 Bad Request— What It Means and How to Fix It

The server cannot process the request due to malformed syntax or invalid parameters.

When It Occurs

Invalid request format, missing required fields.

How to Fix It

Check the request body, headers, and parameters for errors.

Technical Details

Status Code

400

All HTTP Status Codes

Quick reference grouped by category.

Success

Code	Name	Description
200	OK	The request succeeded. The response body contains the requested resource.
201	Created	The request succeeded and a new resource was created.
204	No Content	The server successfully processed the request but returns no content.

Redirect

Code	Name	Description
301	Moved Permanently	The resource has been permanently moved to a new URL.
302	Found (Temporary Redirect)	The resource is temporarily at a different URL.
304	Not Modified	The resource has not changed since the last request (cache hit).

Client Error

Code	Name	Description
400←	Bad Request	The server cannot process the request due to malformed syntax or invalid parameters.
401	Unauthorized	Authentication is required but not provided or invalid.
403	Forbidden	The server understood the request but refuses to authorize it.
404	Not Found	The requested resource could not be found on this server.
405	Method Not Allowed	The HTTP method is not allowed for the requested resource.
408	Request Timeout	The server timed out waiting for the request.
409	Conflict	The request conflicts with the current state of the resource.
410	Gone	The resource is permanently deleted and won't be available again.
422	Unprocessable Entity	The request was well-formed but contains semantic errors.
429	Too Many Requests	The user has sent too many requests in a given time (rate limiting).

Server Error

Code	Name	Description
500	Internal Server Error	The server encountered an unexpected condition.
502	Bad Gateway	The gateway received an invalid response from the upstream server.
503	Service Unavailable	The server is temporarily unavailable (overloaded or maintenance).
504	Gateway Timeout	The gateway did not receive a timely response from the upstream server.

Frequently Asked Questions — HTTP 400

What does HTTP 400 mean?: HTTP 400 Bad Request means: The server cannot process the request due to malformed syntax or invalid parameters. It is a Client Error status code (4xx range). Invalid request format, missing required fields.
When is HTTP 400 returned?: A server returns HTTP 400 Bad Request in the following situation: Invalid request format, missing required fields.
How do I fix HTTP 400?: Check the request body, headers, and parameters for errors.
Is HTTP 400 a client or server error?: HTTP 400 is a client error (4xx range), meaning the problem is on the client side — the request was invalid, unauthorized, or the resource was not found.

Loading Legacy

All HTTP Status Codes

Quick reference grouped by category.

Success

Code	Name	Description
200	OK	The request succeeded. The response body contains the requested resource.
201	Created	The request succeeded and a new resource was created.
204	No Content	The server successfully processed the request but returns no content.

Redirect

Code	Name	Description
301	Moved Permanently	The resource has been permanently moved to a new URL.
302	Found (Temporary Redirect)	The resource is temporarily at a different URL.
304	Not Modified	The resource has not changed since the last request (cache hit).

Client Error

Code	Name	Description
400←	Bad Request	The server cannot process the request due to malformed syntax or invalid parameters.
401	Unauthorized	Authentication is required but not provided or invalid.
403	Forbidden	The server understood the request but refuses to authorize it.
404	Not Found	The requested resource could not be found on this server.
405	Method Not Allowed	The HTTP method is not allowed for the requested resource.
408	Request Timeout	The server timed out waiting for the request.
409	Conflict	The request conflicts with the current state of the resource.
410	Gone	The resource is permanently deleted and won't be available again.
422	Unprocessable Entity	The request was well-formed but contains semantic errors.
429	Too Many Requests	The user has sent too many requests in a given time (rate limiting).

Server Error

Code	Name	Description
500	Internal Server Error	The server encountered an unexpected condition.
502	Bad Gateway	The gateway received an invalid response from the upstream server.
503	Service Unavailable	The server is temporarily unavailable (overloaded or maintenance).
504	Gateway Timeout	The gateway did not receive a timely response from the upstream server.

Frequently Asked Questions — HTTP 400

What does HTTP 400 mean?

HTTP 400 Bad Request means: The server cannot process the request due to malformed syntax or invalid parameters. It is a Client Error status code (4xx range). Invalid request format, missing required fields.

When is HTTP 400 returned?

A server returns HTTP 400 Bad Request in the following situation: Invalid request format, missing required fields.

How do I fix HTTP 400?

Check the request body, headers, and parameters for errors.

Is HTTP 400 a client or server error?

HTTP 400 is a client error (4xx range), meaning the problem is on the client side — the request was invalid, unauthorized, or the resource was not found.