Published by Is It Down Right Now Technical Team • Updated August 2026

Whenever you navigate to a webpage, your browser communicates with the remote web server via the Hypertext Transfer Protocol (HTTP/HTTPS). The server responds with a 3-digit status code that informs your client whether the request succeeded, was redirected, or encountered an error.

Overview of HTTP Status Code Classes

• 1xx (Informational): The request was received and the server is continuing the process.
• 2xx (Success): The action requested by the client was successfully received, understood, and accepted (e.g. 200 OK).
• 3xx (Redirection): Further action must be taken by the client to complete the request (e.g. permanent or temporary redirects).
• 4xx (Client Errors): The request contains bad syntax or cannot be fulfilled due to client-side restrictions or missing files.
• 5xx (Server Errors): The server failed to fulfill an apparently valid request due to internal bugs, crashes, or upstream timeouts.

Common 4xx Client Errors Explained

400 Bad Request

The server cannot process the request due to malformed request syntax, invalid routing data, or corrupted cookies. Fix: Clear cookies for that specific domain.

401 Unauthorized & 403 Forbidden

401 Unauthorized occurs when credentials (login) are required. 403 Forbidden occurs when the server recognizes your identity but refuses to grant access (often triggered by IP blocklists, geographic restrictions, or security firewalls like Cloudflare WAF).

404 Not Found

The requested URL path does not exist on the server. The website itself is usually online, but the specific page, file, or post was deleted, renamed, or mistyped.

429 Too Many Requests

The user or application has sent too many requests in a given amount of time (rate limiting). Often seen when scraping data or refreshing too rapidly.

Common 5xx Server Errors (Website Down Scenarios)

500 Internal Server Error

A generic "catch-all" error indicating that the web server encountered an unexpected condition that prevented it from fulfilling the request. Common causes include unhandled database exceptions, PHP fatal errors, or faulty .htaccess configuration files.

502 Bad Gateway

The server was acting as a gateway or proxy (such as Nginx, Apache, or a Load Balancer) and received an invalid response from the inbound upstream server (such as PHP-FPM, Node.js, or an application server).

503 Service Unavailable

The server is currently unable to handle the request due to temporary overloading or scheduled maintenance. It indicates that the server is alive but has exhausted its CPU, RAM, or database connection pool.

504 Gateway Timeout

The proxy server did not receive a timely response from an upstream server. This frequently happens when long-running database queries freeze or background worker scripts hang.

Cloudflare Errors (520, 521, 522, 524)

• Error 521: Web Server Is Down — The origin web server refused the connection from Cloudflare's edge network.
• Error 522: Connection Timed Out — Cloudflare could not complete the TCP handshake with the origin server within 15 seconds.
• Error 524: A Timeout Occurred — Cloudflare successfully connected to the origin server, but the origin server failed to reply with HTTP data before the timeout window expired.

Troubleshooting Matrix: What Should You Do?

Status Code	Is it You or the Site?	Best Action
200 OK	Site is healthy	If it won't load for you, clear your cache
403 Forbidden	Client permission issue	Disconnect VPN / disable aggressive adblockers
404 Not Found	Broken link / Missing page	Check URL spelling or use site search
500 / 502 / 503 / 504	Server is crashed/overloaded	Wait 10–15 minutes for site admins to fix