HTTP Status Code Lookup — every 1xx–5xx code explained

An HTTP status code lookup is one of the most reached-for references in web development, because a three-digit number is all a server gives you to explain what just happened to a request. This tool covers every standard code from the 1xx informational class through the 5xx server-error class — its official name, which category it belongs to, what it actually means, and when you should use it instead of a similar-looking neighbor.

Arb Digital's team checks this table constantly, both when debugging API integrations and when auditing a client's site for SEO issues caused by the wrong status code being returned on a redirect, a deleted page, or a maintenance window. We built this searchable version so anyone can get the same answer in seconds without digging through a spec document.

What This HTTP Status Code Lookup Does

Type a code number or a keyword into the box above and the reference table filters instantly to matching rows — search "404" to jump straight to it, or search "redirect" to see every 3xx code at once. Click Look Up (or just type an exact code) and the panel above shows that code's class, category, whether it's typically cacheable, and how common it is in real-world traffic. Every code and its description is embedded directly in this page's JavaScript, so the lookup works instantly with no network request and no delay.

HTTP status codes are grouped into five classes by their first digit, and knowing the class alone tells you a lot before you even read the specific code. 1xx codes are informational and rarely seen by application developers. 2xx codes mean success. 3xx codes mean redirection. 4xx codes mean the client made a request the server won't fulfill as-is. 5xx codes mean the server itself failed. This tool's reference table is organized so you can scan by class first, then narrow down to the exact code you need.

How to Use the Lookup

1. Search by code. Type a three-digit number like 301 or 503 to jump directly to it in the table, and click Look Up to populate the summary panel above.
2. Search by keyword. Type words like "redirect," "unauthorized," "rate limit," or "maintenance" to find codes by what they do rather than their number.
3. Read the category column. Codes are tagged as Informational, Success, Redirection, Client Error, or Server Error so you can see the class at a glance even while scrolling a filtered list.
4. Check the "when to use it" guidance. Many codes look similar on paper but have very different practical implications — the meaning column spells out the distinction in plain language.
5. Cross-reference with the SEO section below if you're deciding between codes for a redirect, a removed page, or a maintenance window — the wrong choice can quietly hurt search rankings for months.

The Five HTTP Status Classes, Explained

The MDN HTTP status reference is the authoritative public documentation this tool draws its definitions from, and it groups every code the same way the HTTP specification does. 1xx Informational codes are interim responses telling the client to keep going — for example 100 Continue tells a client its request headers were accepted and it should send the body. 2xx Success codes confirm the request worked, with 200 OK being by far the most common, alongside 201 Created for resource creation and 204 No Content for successful requests with no body to return. 3xx Redirection codes tell the client to look somewhere else for the resource, which is where a lot of subtlety lives (covered in detail below). 4xx Client Error codes mean the request itself was the problem — bad syntax, missing authentication, or a resource that doesn't exist. 5xx Server Error codes mean the server accepted a perfectly valid request but failed to fulfill it, whether from a bug, an overload, or a dependency outage.

301 vs 302 vs 308 — The Redirect Codes That Actually Matter for SEO

This is the single most consequential distinction in this entire table for anyone running a website. 301 Moved Permanently tells both browsers and search engines that a URL has permanently relocated — search engines will transfer the old page's ranking signals to the new URL over time, which is exactly what you want when you rename a page, merge content, or migrate a domain. 302 Found (historically called "Moved Temporarily") signals a temporary redirect — search engines are far more cautious about transferring ranking value here, because the implication is that the original URL will come back, so the old page tends to stay indexed and keep its own signals rather than consolidating into the new one. 308 Permanent Redirect behaves like 301 for SEO purposes but adds one technical guarantee 301 doesn't: it forces the browser to preserve the original HTTP method and request body on the redirect, which matters for API calls and form submissions using POST, PUT, or PATCH. There's also 307 Temporary Redirect, which is the same method-preserving upgrade to 302. The practical rule: if a page or domain change is permanent, use 301 (or 308 if the request method must be preserved); if it's genuinely temporary — like a maintenance page or a personalized redirect based on login state — use 302 or 307, and never use a temporary redirect for something that's actually permanent, because it slows down how quickly search engines pass ranking signals to the new location.

404 vs 410 — Not Found Isn't Always the Right Signal

Both codes tell a visitor "this page isn't here," but they say very different things to a search engine crawler. 404 Not Found is the default, general-purpose "nothing at this address" response — it's appropriate when a URL never existed, when it might come back, or when you're simply not sure. Search engines will keep retrying a 404'd URL periodically for a while before dropping it from the index, on the assumption it might return. 410 Gone is a stronger, more deliberate signal that means "this resource existed and has been intentionally and permanently removed, and it is not coming back." Google's own documentation treats 410 as a faster, cleaner signal to deindex a URL than 404, which makes it the better choice when you've deliberately deleted a product, a discontinued service page, or old content you never intend to restore. Using 410 instead of 404 for genuinely permanent removals can meaningfully speed up how quickly a stale, low-value URL stops competing for crawl budget and stops showing up in search results.

503 for Maintenance — and Why 200 or a Silent Timeout Is a Mistake

When a site needs to go down for maintenance or deployment, the correct HTTP status code to serve is 503 Service Unavailable, paired with a Retry-After header if you know roughly how long the downtime will last. This tells search engines "this is temporary, please keep the existing indexed pages and try again later" — which is exactly the behavior you want during a short maintenance window. The common mistake is serving a maintenance page with a 200 OK status: search engines have no way to distinguish that from a legitimate content change, so a prolonged maintenance page returning 200 risks having its thin "we'll be back soon" content actually indexed in place of your real pages, which can tank rankings for the URLs affected. An even worse mistake is letting the maintenance window simply time out or return a 5xx without any status at all in a way monitoring tools can't detect — always confirm your maintenance middleware is explicitly setting 503, not relying on a proxy's default error page.

Common Client and Server Codes Beyond the SEO Basics

• 401 Unauthorized means authentication is required and either missing or invalid — despite the name, it's about authentication, not authorization.
• 403 Forbidden means the server understood the request and the client is identified, but access is deliberately denied regardless of credentials.
• 429 Too Many Requests is the standard rate-limiting response, and well-behaved clients should respect its Retry-After header rather than retrying immediately.
• 500 Internal Server Error is a generic catch-all for an unhandled server-side failure — useful for alerting, but too vague to debug from alone; check application logs for the real cause.
• 502 Bad Gateway and 504 Gateway Timeout both indicate a problem with an upstream server (like a backend API or database) rather than the server that received the original request, which is a key clue when debugging multi-tier infrastructure.

Common Mistakes to Avoid

• Using 302 for permanent moves. This delays or prevents search engines from consolidating ranking signals onto the new URL — use 301 or 308 instead.
• Returning 200 for a maintenance or error page. Always match the status code to reality; a 200 on broken content confuses both search engines and monitoring tools.
• Confusing 401 and 403. 401 means "who are you, please authenticate"; 403 means "I know who you are, and the answer is still no."
• Serving 404 for intentionally deleted content. Use 410 Gone when removal is deliberate and permanent, so search engines deindex the URL faster.
• Ignoring redirect chains. Multiple hops (301 → 301 → 301) waste crawl budget and slow page loads; always redirect directly to the final destination URL.

Related Free Tools From Arb Digital

Pair this HTTP status code lookup with our MIME Type Lookup when debugging content-type headers, or the User-Agent Parser when investigating traffic from a specific browser or bot. Working with raw characters and encodings? Try the ASCII Table or the Base64 Encoder/Decoder. You'll find every free utility we've built in the free online tools hub.

Frequently Asked Questions

This HTTP status code lookup runs entirely in your browser — no data is sent to any server, and no signup is required.