You mention that you can't add plugins, so I assume you mean an admin panel or some type of server that isn't source? Here's my take on the idea:
This is certainly possible, at least with source servers. I recall using a game server library for nodejs once, it was called
node-gamedig. It displayed scores and player count for an ongoing match.
I'm sure there's a way to get this information natively with the IP and some creative pinging/packet retrieval given the knowledge, though if the backend is node I'd recommend using gamedig.
For something simpler, you could try to get the game info with the steam:// protocol but I believe the only way to see info is if the server isn't responding as it'll just connect you. (steam://connect/)