How to check if your site is actually up for users
Why internal testing often hides real problems, and how to verify availability from the outside world.
One of the most common phrases during an incident is: "It works for me."
The admin dashboard loads. The API responds. Nothing looks obviously wrong.
And yet, users report errors, slowdowns, or complete failures.
This happens because most checks are performed from inside the same network, region, or environment. Cached DNS, existing sessions, VPNs, and internal routing can all make a site appear healthy when it isn't.
From a user's perspective, the experience can be very different.
In this article, we'll look at why internal checks often lie, how users can experience issues you can't reproduce, and how to quickly verify whether a site is actually reachable from the outside world.
Why "it works for me" is a dangerous assumption
When something appears to work on your machine, the natural instinct is to assume the problem is on the user's end. Maybe they have a slow connection. Maybe they're doing something wrong. Maybe they just need to refresh.
This instinct is often wrong, and acting on it can extend incidents significantly.
The fundamental issue is that your environment is not representative of your users' environments. You're testing from a position of privilege: direct network access, fresh DNS resolution that may have propagated to your ISP, authenticated sessions that bypass public routing, and proximity to the servers you're trying to reach.
When you check if a site is up by loading it in your browser, you're not asking "is this site up?" You're asking "can I, specifically, reach this site right now?" Those are different questions with potentially different answers.
Real incidents often affect a subset of users based on geography, ISP, device type, or timing. If you're not in that subset, you won't see the problem, even though it's very real for everyone who is.
Internal checks vs external reality
Several technical factors create a gap between what you see internally and what users experience externally. Understanding these helps explain why your testing can be misleading.
DNS caching. Your computer, your router, and your ISP all cache DNS records. If you recently visited the site, you might be using a cached IP address that's different from what new visitors resolve. A DNS change that broke resolution for new users won't affect you until your cache expires.
VPN and corporate networks. If you're on a VPN or corporate network, your traffic may route through different paths than public traffic. Some companies route internal traffic directly to their servers, bypassing public infrastructure entirely. What works on the VPN may not work on the public internet.
Authenticated sessions. If you're logged in, your requests may be handled differently. Load balancers sometimes route authenticated traffic to different server pools. Your session might be sticky to a healthy server while anonymous users get routed to an unhealthy one.
Geographic proximity. If you're in the same region as your servers, your requests travel a shorter path with fewer opportunities for failure. Users on other continents traverse more network hops, CDN edges, and potential points of failure.
Browser caching. Your browser may be serving cached assets that no longer exist on the server. The page looks fine to you because it's assembled from local cache, while new visitors get 404 errors or broken resources.
Common situations where users see something different
Understanding specific scenarios helps illustrate why external verification matters. These situations come up regularly in production environments.
DNS propagation after changes. You updated your DNS records, and from your machine everything resolves correctly. But DNS propagation isn't instant or uniform. Some users' ISPs may still have the old records cached for hours or even days. Until propagation completes globally, different users will reach different IP addresses.
CDN edge failures. Content delivery networks have nodes distributed globally. If an edge node in a specific region fails or serves stale content, users in that region experience problems while users elsewhere (and your internal tests from a different region) see no issues.
Routing and peering issues. Internet traffic doesn't travel in a straight line. It hops through multiple networks based on peering agreements. A problem with routing between two ISPs can make your site unreachable for users on one ISP while users on others have no issues. These problems are invisible from inside your network.
Geographic or IP-based blocking. Firewall rules, rate limiting, or geo-blocking might be more aggressive than intended. Users from certain countries or IP ranges might be blocked while your internal IPs are whitelisted. You test from a trusted IP and see no problems.
SSL certificate issues. A renewed certificate might be installed correctly on most servers but missing on one. Or certificate chain issues might affect certain clients but not others. Your browser might have the intermediate certificates cached from a previous visit.
Load balancer misconfiguration. After a deployment, one server in your load balancer pool might be unhealthy. If you're session-sticky to a healthy server, every request works. But a percentage of new users hit the bad server and experience failures.
Why traditional uptime dashboards can be misleading
Many teams have monitoring in place that shows uptime percentages and green status indicators. This creates confidence that's sometimes misplaced.
The limitation of most uptime dashboards is that they check from a single location or a small set of locations. If your monitoring server is in the same data center as your application, it's essentially doing the same internal check you do manually. It doesn't represent the global user experience.
Basic uptime checks also tend to perform simple operations: a ping, a TCP connection, or an HTTP request that expects a 200 response. These can return success even when the actual user experience is broken. A server can respond with 200 OK while serving an error page, missing content, or a broken application state.
Additionally, monitoring intervals create gaps. If your check runs every minute, a 30-second outage might fall between checks. Your dashboard shows 100% uptime while users during that window experienced a complete failure.
This isn't to say uptime dashboards are useless. They're valuable for catching sustained outages and tracking long-term reliability. But they shouldn't be the only tool you use to answer "is my site working for users right now?"
When you just need a quick external answer
There are moments during incidents where you need a fast, definitive answer from outside your bubble. Not a deep diagnostic, not a comprehensive report, just a simple: "Can someone from the outside reach this site right now?"
During user-reported incidents. A user says the site is down, but it works for you. Before spending time debugging or dismissing the report, you need to confirm whether the problem is real and widespread, or isolated to that specific user.
After infrastructure changes. You just pushed a deployment, changed DNS, or modified firewall rules. Everything looks good from your end. A quick external check confirms that the change didn't break public access.
When monitoring shows green but something feels off. Support tickets are increasing. Social mentions suggest problems. But your dashboard is green. An external check can reveal whether the monitoring is missing something.
Before making an announcement. You think you've fixed an issue and want to confirm before telling users. An external verification helps avoid the embarrassment of declaring victory prematurely.
When debugging network issues. You suspect DNS, CDN, or routing problems. Testing from your own network can't confirm these. You need a request that follows the same path a typical user's request would follow.
What a user-perspective uptime check should do
Not all external checks are equally useful. A good user-perspective uptime check has specific characteristics that make it reliable for diagnosing real issues.
Requests from a neutral location. The check should originate from outside your network, your data center, and your cloud provider. Ideally, it comes from infrastructure that has no special relationship with your services, mimicking a random user's path.
Fresh DNS resolution. Every check should perform a new DNS lookup rather than using cached results. This reveals DNS propagation issues that wouldn't show up if the checking service had the records cached.
Real HTTP request. A proper check makes an actual HTTP or HTTPS request, not just a ping or TCP connection. This tests the full stack: DNS, network, TLS handshake, and application response. It catches issues that lower-level checks miss.
Response validation. Beyond just checking for a 200 status, useful checks can verify that the response contains expected content. A page that returns 200 but shows an error message isn't really "up" in any meaningful sense.
Speed and simplicity. During an incident, you need answers fast. A check that takes minutes to run or requires complex configuration isn't helpful when you're under pressure. The best tools provide immediate results with minimal friction.
Clear, actionable output. The result should tell you what you need to know without interpretation. Is it up or down? What was the response time? What status code? What error, if any? Ambiguous or overly technical output slows down decision-making.
Final thoughts
External uptime checks are diagnostic tools, not replacements for comprehensive monitoring. They serve a specific purpose: quickly answering whether a site is reachable from outside your environment when you have reason to doubt your internal view.
The "it works for me" problem is real and common. Internal networks, cached data, and privileged access create blind spots that can extend incidents and frustrate users. Recognizing this limitation is the first step toward better incident response.
When users report problems you can't reproduce, the answer isn't to dismiss their experience. It's to verify from a perspective closer to theirs. An external check takes seconds and can immediately clarify whether you're dealing with a real incident or an isolated issue.
The goal isn't to check obsessively. It's to have a reliable way to step outside your bubble when uncertainty arises. During incidents, reducing uncertainty is valuable. Knowing whether your site is actually reachable lets you focus on the right problems and communicate accurately with users.
Ultimately, what users experience is what matters. Any tool that helps you see what they see, rather than what your privileged position shows you, is worth having in your toolkit.
Related resources: If you want to quickly test external reachability, the free uptime checker can provide a user-perspective view of your site's availability.