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A2S Notes

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福狼 edited this page Jul 8, 2026 · 2 revisions

addons/a2s is used for querying game servers directly.

It is different from Steam Web API calls.

Web API vs A2S

Steam Web API A2S
HTTP-based UDP-based game server query
Queries Steam platform data Queries a specific game server
Uses SDK client and credentials when needed Does not use Steam Web API key
Good for player profiles, achievements, app data Good for server info, players, rules

client.API.GameServersService.GetServerList is a Steam Web API discovery helper. It returns server candidates from Steam's Web API side; use A2S afterward when you need current server info, players, or rules.

Supported Query Types

The A2S addon exposes common server query operations:

  • info
  • players
  • rules

Examples

Server info:

go run ./examples/a2s -server 1.2.3.4:27015 -query info

Players:

go run ./examples/a2s -server 1.2.3.4:27015 -query players

Rules:

go run ./examples/a2s -server 1.2.3.4:27015 -query rules

Related Packages

  • addons/a2s
  • addons/a2s/master
  • addons/a2s/scanner

Practical Advice

  • Treat A2S as network probing against game servers.
  • Treat GetServerList results as candidates, not proof that every server still matches every filter.
  • Expect timeouts and partial failures.
  • Use bounded concurrency when scanning.
  • Do not mix A2S error handling with Web API error handling.
  • Keep A2S as an addon so the core Web API client stays small.

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