Website Uptime / Is It Down Checker

How uptime checking works

Website uptime checking is the practice of periodically testing whether a web server is reachable and responding correctly. The most basic check is an HTTP GET request: the monitoring system sends a standard HTTP request to the target URL and waits for a response. If the server responds with a valid HTTP status code within a configurable timeout, the site is considered "up." If the connection times out, DNS resolution fails, the TCP handshake is refused, or the server returns a 5xx error, the site is considered "down." This simple check reveals a lot about the health of a web service, but it has important limitations that every user should understand.

This tool performs a single HTTP request from Cloudflare's global network. It measures the total time from the initial request to the receipt of the first byte of the response (TTFB or Time to First Byte). This metric includes every step of the network stack: DNS resolution (looking up the IP address for the hostname), TCP connection establishment, TLS handshake (if HTTPS), HTTP request transmission, server processing time, and the start of the response transmission. A slow TTFB can indicate any problem along this chain — a slow DNS provider, congested network path, overloaded server, or inefficient application code.

Professional uptime monitoring services deploy probes in multiple geographic regions and datacenters, checking every minute or even every 30 seconds. They track historical uptime percentages (usually reported as "99.9% uptime" over the last 30 days), generate alerts via email, SMS, or webhook when downtime is detected, and provide dashboards showing response time trends over time. This tool provides none of that — it is a single point-in-time check from one location. However, that single check is often enough to answer the question "is the site currently reachable?" with reasonable confidence.

What uptime really means

In the context of web services, uptime is the percentage of time a website or service is accessible and functioning correctly. A 99.9% uptime SLA means the service can be down for no more than about 8.76 hours per year. 99.99% uptime allows only 52.56 minutes of downtime annually. These numbers sound impressive, but they mask important nuances. A service may technically be "up" (responding to HTTP requests) while providing a degraded experience — slow page loads, missing assets, or incorrect data. Conversely, a service may be "down" for users in one region but perfectly reachable from another.

Many factors beyond the server itself can cause downtime from the user's perspective. DNS propagation delays after a nameserver change can make a site unreachable for hours. CDN outages can prevent users from loading cached assets even though the origin server is healthy. DDoS attacks can saturate network links and make services unreachable. Routing issues between ISPs can cause packet loss and timeouts. Firewall rules and web application firewalls (WAFs) can block legitimate traffic. ISP-level filtering or government censorship can prevent access entirely. This tool cannot diagnose any of these issues — it only tells you whether Cloudflare's network can reach the target server right now.

How to interpret results

When this tool returns a status of "Up," it means the target server responded to an HTTP request from Cloudflare's network. A 200 OK response is the ideal result — the server is reachable and the page loads correctly. A 301 or 302 redirect is also normal if the server is configured to redirect HTTP to HTTPS or from a bare domain to www. A 401 or 403 indicates the server rejected the request (possibly expecting authentication), but the server itself is up. A 404 indicates the requested URL was not found, but the server is running. Only a 5xx error (500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable) or no response at all indicates a server-side problem.

When the tool returns "Down," the first step is to verify from another device or network. If you can access the site from your phone on mobile data but your desktop on a home ISP cannot, the issue is likely with your ISP or network configuration. If the site is inaccessible from every device and network you try, use a global CDN status page or a multi-region monitoring service to confirm a widespread outage. This tool's single-region check is a useful first step, but it should never be the only data point you rely on to determine whether a service is experiencing an outage.

Frequently asked questions