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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states the tool creates/joins a session, but it doesn't disclose side effects, whether it blocks, what 'joins a waiting lobby' does when no lobby exists, whether it mutates state for other players, or auth/permission requirements. It also doesn't describe what outputs an agent should expect — partly mitigated by the existence of an output schema, but the behavioral burden is not met.

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?

The description is two terse sentences with no fluff or repetition. It is front-loaded with the primary action ('Create or join a game session'). However, it is arguably too short to be genuinely helpful given the 0% parameter coverage, so a 4 is fitting.

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?

Given 6 parameters, 0% schema description coverage, no annotations, and an output schema (which exists), the description is incomplete. It doesn't explain return values beyond vague hints, doesn't distinguish create vs. join flow, doesn't cover parameter behavior, and doesn't address failure modes or lobby waiting semantics. Output schema existence helps but doesn't compensate for the missing parameter/behavioral context.

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?

Schema description coverage is 0%, so the description must compensate for the 6 parameters. The description explains only 'game session', 'match', 'lobby' at a high level and adds no meaning for bots, players, match_id, opponent, or difficulty. For instance, it doesn't clarify whether 'players' means max players, whether 'difficulty' applies only to bots, or what 'opponent' accepts. This is a significant gap.

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 states a specific verb ('Create or join') and resource ('game session'), and names two creation modes ('Starts a match or joins a waiting lobby'). It distinguishes the tool from the sibling list (arcade_state, arcade_status, arcade_wait are all adjacent session-management tools) at a high level, though it doesn't explicitly name any sibling it is not. Clear enough to identify purpose, with a small gap in differentiating from arcade_wait or arcade_state.

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?

No guidance is given for when to use this tool vs. the many siblings such as arcade_state, arcade_wait, or arcade_history. It does not say when to create vs. join, what preconditions exist (e.g., whether game_id must exist, whether a match_id is required to join), or when to prefer a sibling. The usage context is implied at best.

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