A good Team Fortress 2 server is a bit like a good auto mechanic: Finding either can be tricky. Valve has been considering ways to make the process easier for "a while now" and has finally settled on a remarkably simple method of rating servers that won't penalize games with custom rules and isn't susceptible to "lies" from the servers themselves.
"After kicking around some proposals, we came up with a simple system built around the theory that player time on a server is a useful metric for how happy the player is with that server," Valve programmer Robin Walker wrote on the Team Fortress 2 blog. "It's game rules agnostic, and we can measure it on our Steam backend entirely from Steam client data, so servers can't interfere with it. We already had this data for all the TF2 servers in the world, allowing us to try several different scoring formulas out before settling on this simple one that successfully identified good & bad servers."
The formula in question assigns every new server in the master server list a score of zero, then deducts 15 points from that score every time a player connects. For each minute a player stays connected, one point is added to the score, up to a maximum of 45 points per player. Servers that have a large number of players joining and leaving quickly will score badly while those that keep keep people connected and playing will move up on the rating list.
"The bulk of servers in the world are doing a pretty good job of providing an experience that's expected by the people joining them," Walker said, referring to server data from the previous week. "More importantly, it's really easy to see what servers are bad. Overlaying the number of players connecting to the servers illustrates how nasty an effect these bad servers are having on players. The very worst servers attract a large number of connections, mostly because they're lying in ways that make them look like a very attractive server at all times."
Valve has delisted the "really bad servers" so players will no longer see them in the master server list, but Walker claimed that's only the "first step" in the plan. "After that, we're going to keep improving our ability to measure this kind of problem," he said.