Domains break quietly. A certificate expires, a DNS record is changed, a www variant stops redirecting, and the first sign is a drop in traffic weeks later. The Check domains button on the plugin's settings screen tests every domain you saved and tells you what is wrong in one table.

How to use it

Open the plugin, press Check domains and wait a few seconds. The check uses the domains as they are saved, so save your changes first. Every row gets a status - OK, a warning or an error - with one sentence of explanation.

What is checked, per domain

• DNS - the domain resolves, and the addresses it resolves to are shown.
• HTTPS - the domain reaches this Joomla site. The check asks the domain a question only this site can answer correctly, so a domain that points at another server or another Joomla is caught.
• Certificate - valid for this name, with a warning when it expires within two weeks and an error when it has expired.
• HTTP to HTTPS - the plain http address redirects to https.
• www variant - the variant you did not configure redirects to the one you did. A variant that does not resolve at all is fine and says so.
• robots.txt - the domain serves the robots.txt you filled in for it, if you filled one in.

What is checked once, for the whole site

• Sessions - sessions are stored in the database, which is what makes logging out work on every domain.
• Language filter - the core plugin Domain per Language depends on is enabled.
• SEF URLs - search engine friendly URLs are on.

Not reachable from the server

Some hosting setups cannot reach their own public address: the server asks for your domain, the request goes out and never comes back. The check then says not reachable from the server and offers a link to open the test in your own browser. A 64-character code in that page means the domain does reach this site and only the server itself cannot see it. That is a hosting matter, not a plugin one; your visitors are not affected.

Safety

The check runs only for administrators who may manage plugins, and only against the domains you saved: it never sends a request to a host taken from the browser. Every connection has a five second time-out, and redirects are not followed, so a chain of redirects cannot hide a problem.