Your server must publish public rooms over federation (see how to add your server). If your server does not publish public rooms over federation, there are still ways to add your room to the index.

Option 1: get your own Matrix server

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The MRS project in general, and this instance specifically is developed and maintained by managed Matrix servers provider etke.cc, so while we are a bit biased, we are sure that you will be satisfied with the service, and we can guarantee you that with a Matrix server from us, you won't have any issues with publishing your public rooms over federation!

Consider this a shameless advertising, but the fact you opened that page means we are doing a good job.

However, if that's not an option for you, there are other ways to add your room to the index described below.

Option 2: ask a different server to publish your room

Matrix protocol allows publishing rooms in the public rooms directory, even if they are not hosted on the same server. You can ask a server administrator of a different Matrix server to publish your room into their public rooms directory.

Note that the alias of the room could be left unchanged (i.e., pointing to your server).

Keep in mind that the usual rules apply to the server, and to the room (it has to be public, federated, have an alias, and it should be allowed to join)