Free diagnostic tools for any website
Knowing a site is down is the first question. These are the next four - What its DNS says, whether its certificate expired, what an uptime figure really permits, and what the outage is costing. All free, all without an account except where a record contains someone’s personal data.
Check whether a website is down Start here
Request any address from our servers, on a different network, resolver and route from yours, and see exactly which stage of the request failed. Every other tool on this page answers a question that follows from this one.
The 7 questions that follow
DNS and domain lookup
Every record a domain publishes: Addresses, name servers, mail, verification records, registrar and who hosts it.
Use it When a site is unreachable and you need to know whether the problem is the name or the server behind it.SSL certificate checker
Who issued a certificate, what it covers, and exactly how many days are left before browsers start refusing the site.
Use it When a site loads for some people and shows a security warning for others, or stopped working overnight for no obvious reason.HTTP header inspector
Every response header a site sends, the redirect chain it took to get there, and which security headers are missing.
Use it When a site loads but behaves oddly - Caching that will not clear, a redirect loop, or a mixed-content warning.HTTP status code reference
Every status code a browser can show you, what it actually means, and whether it is yours to fix or theirs.
Use it When you have a number on screen and need to know whether waiting will help.Uptime and SLA calculator
Turn an uptime percentage into the downtime it actually permits, per day, month and year - in both directions.
Use it When you are reading an SLA and want to know what "99.9%" lets a provider get away with.Downtime cost calculator
What an hour offline costs, from revenue, staff time and the orders that never come back.
Use it When you need a number to justify monitoring, redundancy, or a better hosting plan to somebody who controls the budget.Outage error page generator
A ready-made 502/503 page for your server or CDN that sends stranded visitors to a live status page instead of a blank error.
Use it Before your next outage - so the people who hit it are told what is going on and where to check, rather than left staring at "Bad Gateway".Every one of these links back to the checker with the address you were looking at, so you can move between them without retyping anything.
Why these 7 and not forty
There is a well-worn genre of site that publishes a hundred small network utilities, most of which nobody uses and several of which are thin wrappers around the same command. We have deliberately not done that. Each tool here earns its place by being a step somebody actually takes while diagnosing a real outage.
The order people actually work in
The sequence is usually the same. A page will not load, so you check it from somewhere else to find out whether the problem is yours or theirs. If it is theirs, the next question is which part is broken - And that is nearly always either the name or the certificate, which is why those are the two server-side tools here. If the name does not resolve, no amount of server capacity helps. If the certificate expired at midnight, the server is perfectly healthy and every browser is still refusing to load it.
Why two of them run in your browser
The other two are arithmetic rather than network calls, and they answer the questions that come after the outage rather than during it: What the uptime number in your contract actually permits, and what the hour offline cost. Both run entirely in your browser. Nothing you type into them is sent anywhere, because nothing needs to be.
What we do not build
We do not offer a port scanner, and we will not. A hosted port scanner is a free attack tool with a friendly interface: The traffic comes from our address range rather than the user’s, which is the entire appeal to the small number of people who would use it most. The same reasoning rules out anything that enumerates subdomains, brute-forces paths, or sends more than a handful of requests to a target.
The limit every tool here respects
Everything here makes at most a few requests to a host, to the same public endpoints your browser would request anyway. That limit is what lets us run these without an account and without a queue.