HTTP Status Codes
Type a status code number or search by keyword (e.g. "not found", "redirect") to instantly look up any HTTP response code. Leave empty to browse all codes.
How HTTP Status Codes Work
This free HTTP status code reference lets you quickly find the meaning of any HTTP response code. Enter a numeric code like 404 or 502 to get its exact definition, or search by keyword such as "unauthorized" or "gateway" to find all matching status codes. When the input is empty, the tool displays every standard HTTP status code organized by category.
HTTP Status Code Categories
HTTP status codes are three-digit numbers returned by web servers. The first digit defines the category: 1xx codes are informational, 2xx codes indicate success, 3xx codes handle redirection, 4xx codes signal client errors, and 5xx codes report server errors. Each code has a specific meaning defined by IETF RFCs.
Why HTTP Status Codes Matter
Every time your browser requests a web page, the server responds with an HTTP status code before sending any content. These codes tell the client whether the request succeeded, failed, or needs further action. Understanding status codes is essential for web developers debugging API integrations, DevOps engineers monitoring server health, and SEO professionals diagnosing crawl issues.
For example, a 301 redirect tells search engines to permanently update their index, while a 302 redirect is temporary. A 429 status means you are sending too many requests and should slow down. A 503 indicates the server is temporarily unavailable, often during deployments or maintenance windows.
Common Status Codes Every Developer Should Know
While there are dozens of HTTP status codes, a handful appear in nearly every web application. The 200 OK response confirms a successful request. 201 Created is returned after successfully creating a resource via POST. 301 Moved Permanently and 302 Found handle URL redirections. 400 Bad Request means the server cannot process malformed input. 401 Unauthorized and 403 Forbidden deal with authentication and permissions. 404 Not Found is the most recognizable error on the web. On the server side, 500 Internal Server Error and 502 Bad Gateway are the most common failure codes.
Using Status Codes in API Development
RESTful APIs rely heavily on status codes to communicate outcomes. A well-designed API returns 200 for successful reads, 201 for successful creates, 204 for successful deletes with no response body, 400 for validation errors, 404 when a resource does not exist, and 409 for conflict situations like duplicate entries. Properly using these codes makes APIs self-documenting and easier for client applications to handle programmatically.
Privacy and Security
This tool runs entirely in your browser. No data is sent to any server. The complete status code database is embedded in the page, so lookups are instant and work offline after the page loads.
Frequently Asked Questions
What are HTTP status codes?
HTTP status codes are three-digit numbers returned by a web server in response to a client request. They indicate whether the request was successful, redirected, or resulted in an error. The first digit defines the category: 1xx informational, 2xx success, 3xx redirection, 4xx client error, and 5xx server error.
What is the difference between 401 and 403?
A 401 Unauthorized response means the request lacks valid authentication credentials — the user needs to log in. A 403 Forbidden response means the server understood the request and the user may be authenticated, but they do not have permission to access the requested resource.
What does a 502 Bad Gateway error mean?
A 502 Bad Gateway error means the server acting as a gateway or proxy received an invalid response from an upstream server. This commonly occurs when a reverse proxy like Nginx cannot reach the application server behind it, often due to the application crashing or restarting.
Is my data sent to a server when using this tool?
No. The entire HTTP status code database is embedded in the page. All lookups happen locally in your browser using JavaScript. No network requests are made, and the tool works offline once loaded.
What is the difference between 301 and 302 redirects?
A 301 Moved Permanently redirect tells browsers and search engines that the resource has permanently moved to a new URL. A 302 Found redirect indicates a temporary move. For SEO, 301 redirects pass link equity to the new URL, while 302 redirects do not. Use 301 for permanent URL changes and 302 for temporary situations like A/B tests or maintenance pages.