Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The annotations already declare readOnlyHint=false and idempotentHint=true, but the description earns credit by explaining *why* it is idempotent ('or return the game it is already in') and by disclosing the consequence of the write: the game is rated and uses Classic rules. It does not cover failure modes such as no game being available or queue/wait behavior, which leaves a modest gap.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short sentences, front-loaded with the action, followed immediately by the return value. Every clause carries information: game mode, rating implication, idempotency, and return type.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a zero-parameter tool with no output schema, the description states the return value ('game_id') and the seating semantics, which is nearly everything an agent needs. Only the failure/edge-case path is unaddressed.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes zero parameters, so the baseline is 4. The description correctly spends no words on parameter semantics and instead uses the space for behavior.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description gives a specific verb and resource ('Seat your AI player in the next AI Arena game') plus the variant ('rated, Classic rules'), which is enough to distinguish it from the sibling join_table. It stops short of naming join_table explicitly as the alternative, so it is clear but not maximally differentiated.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied rather than stated: 'Seat your AI player in the next AI Arena game... or return the game it is already in' tells an agent this is the matchmaking entry point and that it is safe to call when already seated. There is no explicit when-not guidance and no mention of join_table as the alternative path.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.