What are HTTP status codes every developer should know?

HTTP status codes are three-digit numbers returned by a web server to indicate the outcome of a client's request. They help browsers, APIs, and applications understand whether a request was successful, redirected, invalid, or failed due to a server issue.

HTTP status codes are grouped into five categories:

1xx – Informational: The request has been received and processing continues.
2xx – Success: The request was successfully processed.
3xx – Redirection: Additional action is required to complete the request.
4xx – Client Errors: The request contains an error or cannot be fulfilled by the server.
5xx – Server Errors: The server encountered an error while processing a valid request.
Common HTTP Status Codes Every Developer Should Know
1xx – Informational

100 Continue

The initial part of the request has been received.
Mainly used internally between clients and servers.
2xx – Success

200 OK

The request was successful.
Commonly returned for successful GET, PUT, or PATCH requests.

Example:

GET /users/1
→ 200 OK

201 Created

A new resource was successfully created.
Typically returned after a successful POST request.

Example:

POST /users
→ 201 Created

204 No Content

The request succeeded, but there is no response body.
Often used after deleting a resource.

Example:

DELETE /users/1
→ 204 No Content
3xx – Redirection

301 Moved Permanently

The requested resource has permanently moved to a new URL.
Browsers automatically redirect future requests.

Example:

http://example.com
→ https://example.com

302 Found

Temporary redirect.
The resource is temporarily available at another location.

304 Not Modified

The requested resource has not changed since the last request.
Used with browser caching to improve performance.
4xx – Client Errors

400 Bad Request

The request is malformed or contains invalid data.

Example:

POST /users
{
"email": "invalid-email"
}
→ 400 Bad Request

401 Unauthorized

Authentication is required or the provided credentials are invalid.

Example:

Missing or invalid JWT token
→ 401 Unauthorized

403 Forbidden

The user is authenticated but does not have permission to access the resource.

Example:

Regular user trying to access an admin endpoint
→ 403 Forbidden

404 Not Found

The requested resource does not exist.

Example:

GET /users/999
→ 404 Not Found

405 Method Not Allowed

The requested HTTP method is not supported for the resource.

Example:

DELETE /login
→ 405 Method Not Allowed

409 Conflict

The request conflicts with the current state of the resource.

Example:

Creating a user with an email that already exists
→ 409 Conflict

422 Unprocessable Entity

The request format is correct, but validation fails.

Example:

Password is too short
Email is missing
→ 422 Unprocessable Entity
5xx – Server Errors

500 Internal Server Error

An unexpected error occurred on the server.

Example:

Database connection failed
Unhandled exception
→ 500 Internal Server Error

502 Bad Gateway

A gateway or proxy received an invalid response from an upstream server.

503 Service Unavailable

The server is temporarily unavailable due to maintenance or overload.

504 Gateway Timeout

The upstream server took too long to respond.
REST API Example
API Request Status Code Reason
GET /products 200 OK Products retrieved successfully
POST /products 201 Created Product created successfully
PUT /products/5 200 OK Product updated
DELETE /products/5 204 No Content Product deleted successfully
GET /products/999 404 Not Found Product doesn't exist