HTTP Status Code Reference

What are HTTP Status Codes?

Every time a browser or client makes an HTTP request, the server responds with a three-digit status code that summarizes the outcome. These codes tell you whether the request succeeded, was redirected, failed because of a client mistake, or failed because of a server problem. Understanding them is essential for web development, API integration, and debugging.

This HTTP Status Code Reference lets you search by number, name, or description and browse the most common codes with clear, plain-English explanations. Each code is color-coded by its category so you can instantly tell a success from a redirect or an error.

The Five Status Code Categories

• 1xx Informational — the request was received and the process is continuing
• 2xx Success — the request was successfully received, understood, and accepted
• 3xx Redirection — further action is needed to complete the request
• 4xx Client Error — the request contains bad syntax or cannot be fulfilled
• 5xx Server Error — the server failed to fulfill a valid request

The Most Common Status Codes

200 OK means the request succeeded. 301 Moved Permanently and 302 Found handle redirects, with important SEO implications for which one you choose. 404 Not Found is the familiar broken-link error. 401 Unauthorized and 403 Forbidden relate to authentication and permissions.

On the server side, 500 Internal Server Error is the generic catch-all failure, while 502 Bad Gateway and 503 Service Unavailable point to problems with upstream servers or capacity. 429 Too Many Requests appears when you hit an API's rate limit.

Who Uses This Reference?

Front-end and back-end developers consult status codes when building and consuming APIs, deciding which code to return for a given situation, and debugging why a request behaved unexpectedly. DevOps engineers use them to interpret server logs and monitoring alerts. SEO specialists rely on them to diagnose crawl errors and redirect chains that affect search rankings.

How to Read a Status Code by Its First Digit

The genius of HTTP status codes is that the first digit alone tells you the broad outcome, even if you have never seen the specific code before. A 2xx means success — the request worked. A 3xx means redirection — the resource is somewhere else and the client should follow. A 4xx means a client error — the request itself was wrong, whether a bad URL, missing authentication, or invalid data. A 5xx means a server error — the request was fine, but something failed on the server's side.

This structure makes debugging much faster. The moment you see the leading digit you know which side of the conversation to investigate: a 4xx points you at the request your code is sending, while a 5xx points you at the server or an upstream service. This reference groups and colour-codes every code by that category so you can scan to the right area instantly and read a plain-English explanation of the exact code.

Why Choose Our HTTP Status Code Reference?

This reference is completely free, needs no signup, and runs entirely in your browser. It is searchable by number, name, or description, so you can find the code you need in seconds, and every entry is written in plain English rather than terse spec language. Colour-coding by category lets you tell a success from a redirect or an error at a glance, which makes it a genuinely fast lookup while you are debugging.

The HTTP Status Code Reference is one of more than 200 free tools on ToopTools. If you build or debug APIs regularly, you can pin it to your personalized My Workspace workspace so it sits beside your other developer utilities, always one click away. It works on any modern browser, on desktop and mobile.

Is the HTTP status code reference free?

Yes. It is completely free with no limits and no signup. You can search and browse the status codes as much as you like, as often as you like, without ever creating an account.

What is the difference between 401 and 403?

A 401 Unauthorized means you are not authenticated — the server does not know who you are, and you need to log in or provide valid credentials. A 403 Forbidden means you are authenticated but not allowed — the server knows who you are and is refusing access to this resource regardless. In short, 401 is about identity, 403 is about permission.

What does a 500 error mean?

500 Internal Server Error is a generic catch-all indicating something went wrong on the server while processing an otherwise valid request — often an unhandled exception or misconfiguration. Because it is intentionally vague to the client, diagnosing it means checking the server's own logs, which usually contain the real cause.

Which redirect code should an API return?

It depends on intent. Use 301 Moved Permanently when a resource has a new permanent URL, since clients and search engines will update to it. Use 302 Found or 307 Temporary Redirect for temporary moves. For APIs, 307 and 308 are often preferred because they preserve the original request method, unlike older 301/302 handling.

Why am I getting a 429?

429 Too Many Requests means you have exceeded an API's rate limit — you are sending requests faster than it permits. The response often includes a Retry-After header telling you how long to wait. The fix is to slow down, add backoff and retry logic, or request a higher limit from the API provider.

Who Uses This Reference?

• Front-end developers interpreting responses while consuming APIs
• Back-end developers deciding which code to return for each situation
• DevOps engineers reading status codes in server logs and alerts
• QA engineers asserting on response codes in automated tests
• SEO specialists diagnosing crawl errors and redirect chains

Key Features

• Searchable by number, name, or description
• Covers the common informational, success, redirect, client-error, and server-error codes
• Plain-English explanation for every code
• Colour-coded by category for instant recognition
• Fast, no-signup lookup while you debug
• 100% browser-based and completely free

What does a 404 status code mean?

A 404 means 'Not Found' — the server was reached but could not find a resource at that URL, often due to a broken link, a moved page, or a typo in the address. It is a client-side error in the 4xx range and does not indicate a server fault.

What is the difference between a 301 and a 302 redirect?

A 301 is a permanent redirect, telling browsers and search engines the resource has moved for good and to update their links. A 302 is temporary, signalling the move is short-term and the original URL should be kept. Use 301 for permanent URL changes.