HTTP Status Codes Explained: Complete List & What They Mean

Every time your browser loads a page, the server quietly answers with a three-digit number. You usually never see it — until something goes wrong. Then you meet 404, 500, or the dreaded 502. Understanding these numbers turns the web from a black box into a system you can actually debug.

What Are HTTP Status Codes?

HTTP status codes are three-digit numbers that a web server sends back to a browser to indicate the result of a request. Like delivery status updates: 'delivered', 'address not found', 'sender unavailable'. Every page load, every API call, every image request — all of it gets a status code.

HTTP Status Code Categories (5 Classes)

• 1xx — Informational (request received, continuing).
• 2xx — Success (the request worked).
• 3xx — Redirect (the resource lives elsewhere).
• 4xx — Client error (your request is the problem).
• 5xx — Server error (the server is the problem).

2xx Success Codes Explained

• 200 OK — the most common; the request succeeded and content was returned.
• 201 Created — used in REST APIs when a new resource has been created.
• 204 No Content — success, but there is nothing to send back (common after a DELETE).

3xx Redirect Codes Explained

• 301 Moved Permanently — the SEO-safe permanent redirect; passes most link equity.
• 302 Found — temporary redirect; use carefully, doesn't always pass full SEO value.
• 307 / 308 — method-preserving variants of 302 / 301.

SEO rule of thumb: always use 301 for permanent URL changes so Google transfers ranking signals to the new URL.

4xx Client Error Codes Explained

• 400 Bad Request — malformed request the server can't parse.
• 401 Unauthorized — you're not logged in.
• 403 Forbidden — you're logged in but you don't have permission.
• 404 Not Found — the URL doesn't exist on this server.
• 429 Too Many Requests — rate-limit hit; slow down.

5xx Server Error Codes Explained

• 500 Internal Server Error — generic server crash; check server logs.
• 502 Bad Gateway — upstream server returned an invalid response.
• 503 Service Unavailable — server overloaded or in maintenance.
• 504 Gateway Timeout — upstream server didn't respond in time.

How to Check HTTP Status Codes for Any URL

Frequently Asked Questions

What is the difference between 401 and 403?

A 401 means you are not authenticated — you need to log in. A 403 means you are authenticated but do not have permission to access that resource.

Does a 404 error hurt SEO?

A few 404s are normal and expected. However, large numbers of 404 errors from internal links signal poor site maintenance to Google and can hurt crawl efficiency and rankings.

What is the difference between 301 and 302 redirect?

A 301 is a permanent redirect and passes most SEO link equity to the new URL. A 302 is temporary and may not pass full SEO value. Use 301 for all permanent URL changes.

What causes a 500 Internal Server Error?

A 500 means something went wrong on the web server — usually a misconfigured script, database connection failure, or a resource limit being hit. Check the server's error logs to diagnose.

What does the HTTP 200 OK status mean?

It means the request was successful and the server returned the expected content. It is the most common status code and indicates everything is working normally.