"Is the server down or is it just me?" has a precise answer for a whole family of games, because Valve's server query protocol — A2S — long ago escaped Source-engine games and became the de-facto standard for anything shipped through Steam's server infrastructure. CS2, TF2, Garry's Mod, Rust, ARK, and Palworld all answer (or half-answer) the same three-packet conversation, which means one checker can smoke-test them all.
How A2S works ¶
A2S is a tiny UDP exchange. The client sends an A2S_INFO request; since a 2020 protocol hardening, most servers first reply with a challenge number that you must echo back — this stops the protocol being abused for traffic amplification. The real reply then carries the server's name, map, game, player count and cap, bot count, VAC status, and version. Sibling queries fetch the player list (A2S_PLAYER) and server tags (A2S_RULES). No authentication, no account — the same conversation the in-game server browser has. Our game-server checker runs exactly this exchange and shows the parsed reply; the A2S_INFO smoke test post walks through the raw bytes if you want to do it by hand.
The trap: query port ≠ game port ¶
Most "the checker says down but people are playing" reports come down to probing the wrong port. Games in this family typically run two UDP listeners: the game traffic port and the query port, and they are frequently different numbers.
| Game | Typical game port | Typical query port |
|---|---|---|
| CS2 / TF2 / GMod | 27015 (UDP) | 27015 — usually shared |
| Rust | 28015 (UDP) | 28015 or a dedicated queryport |
| ARK: Survival Evolved / Ascended | 7777 (UDP) | 27015 — separate by default |
| Palworld | 8211 (UDP) | 27015 — separate by default |
These are defaults, not guarantees — hosts renumber them freely, especially on shared machines running many instances. If a server's listing says 1.2.3.4:8211, that's probably the game port; querying it will time out while the server is perfectly healthy. Ask the operator (or the hosting panel) for the query port before concluding anything.
Per-game honesty notes ¶
- CS2 / TF2: the most faithful A2S implementations, as you'd expect. Name, map, players, and version are all dependable.
- Rust: answers A2S properly, and encodes extra state (queue length, build id) into its keywords/tags. Player counts are real, but the join queue means "not full" in the query and "queue: 40" at the door can both be true.
- ARK: reliable A2S on the separate query port; the player list query often returns empty or placeholder entries even when the count is correct. Trust the count, not the names.
- Palworld: the newest and roughest. It speaks enough A2S to prove liveness — a reply means the server is up — but its player-count field has been famously unreliable (often stuck at zero), which is why the developers added a separate REST API for owners. Treat a Palworld A2S reply as an up/down signal and distrust its numbers.
That last point is a good general rule for this whole family, same as with Minecraft's status ping: a reply proves the server is alive; the fields inside are the server's word.
Down for everyone, or just for you? ¶
- Query from outside your network. Run the address (with the query port) through our checker — a reply from our vantage point while your client fails points at your network, VPN, or a region-specific block.
- Separate Steam from the server. If the server browser is empty across all games, the problem may be Steam-side — see is Steam down — not the individual server.
- Timeout vs nothing: UDP has no "connection refused". A dead server and a firewalled query port look identical from outside — both are silence. That ambiguity is inherent to the protocol, so repeated probes over time are worth far more than one snapshot; a monitor gives you exactly that, with alerts when the pattern breaks.
FAQ ¶
Why does the in-game browser show the server but my checker doesn't?
Different port (browser uses Steam's master-server listing, which knows the query port), or the host firewalls query traffic to everyone except Steam's ranges. Confirm the query port first; it explains most disagreements.
Can I check a server behind DDoS protection?
Sometimes. Game-server DDoS mitigation filters UDP aggressively, and some providers drop A2S from unknown sources during an attack. A temporarily silent query while players remain connected is a known artifact of mitigation mode.