Understanding an availability check
When a website will not open, it helps to check it from another network. This tool attempts a TCP connection from DevPicker to the host and port you enter. It gives you one useful piece of evidence about reachability, rather than a verdict on every part of a website.
Which host and port should I enter?
For https://example.com/account, enter example.com as the host and 443 as the port. For an HTTP service, start with port 80. A service running on a custom TCP port needs that port number instead. Checking one port says nothing about whether another port is available.
You can enter a public IPv4 or IPv6 address directly. This can help separate a hostname problem from a connection problem, although it still does not test how a website handles a particular domain name.
What does each result mean?
- Port is reachable: the host accepted a TCP connection from our server. A web application behind that port could still return an error, require a login, or have a certificate problem.
- Could not connect: the connection attempt failed. A closed port, filtering, routing trouble, or an unavailable service could cause this. It does not prove that everyone is affected.
- Check could not run: the input could not be used, the domain could not be resolved, or the address is not eligible for a public check. Correct the input before interpreting availability.
Why can the result differ from my browser?
Your browser and DevPicker reach the host through different networks. A firewall, regional restriction, or temporary routing problem may affect one connection and allow another. Your browser may also use saved cookies, a VPN, or cached DNS information that changes what you experience.
A domain can resolve to several addresses. This tool checks one resolved address, so it does not establish that every server behind the domain is reachable. Large sites may also send different visitors to different servers.
Does an open HTTPS port mean the website works?
No. Accepting a TCP connection on port 443 is only an early step in serving HTTPS. The TLS handshake, certificate verification, HTTP response, and application can fail afterward. If the port is reachable but a page still fails, inspect the browser's error message and use the Redirect Checker to examine HTTP redirects and response codes.
For example, an HTTP 404 means a resource was not found, while a 503 can indicate temporary unavailability. Both can come from a server whose TCP port is reachable. See MDN's HTTP status reference.
What should I try next?
- Confirm the hostname and the port expected by the service.
- Compare another browser or network, such as mobile data instead of Wi-Fi.
- Check the site's official status page for a reported incident.
- If you manage the service, review its logs, listener configuration, and firewall rules.
Private network addresses, loopback addresses, and reserved addresses are not accepted. A device on your home or office network needs to be checked from a network that can reach it.
Is this an uptime monitor?
This is a single check at the time you submit it. It does not keep checking in the background, store an availability history, or send alerts. Recheck after a change, and use ongoing monitoring when you need to measure an outage over time.
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