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

Annotations already declare this is a non-read-only, non-destructive mutation, and the description usefully adds the idempotency retry contract ('reuse the key to retry the same creation'). It says nothing about what gets created, required permissions, or what happens if a different key collides, leaving meaningful gaps for a write operation.

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 terse sentences, front-loaded with the core action and followed by the single most operationally important caveat. Nothing is wasted and nothing is buried.

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?

There is no output schema and no annotation detail beyond the safety hints, so the description should say what the agent receives after creation (e.g., a match identifier) and how optional relay/campaign bind to specific game values. It covers the action and idempotency but leaves the return contract and mode-combination rules unstated.

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 coverage is 75%, with relay, campaign, and idempotencyKey documented inline and only 'game' lacking a description. The description itself adds no parameter meaning, so the schema carries the load, which is consistent with a baseline 3 at this coverage level.

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?

States a specific verb and resource (create a match) with a scope qualifier ('public multiplayer'), which distinguishes it from read_arena_match, list_arena_matches, and join_arena_match. It does not name the siblings it differs from, so it lands below a 5.

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?

The only guidance is retry behavior via the idempotency key; there is no statement of when to create a new match versus joining an existing one, nor any prerequisites. The agent must infer the create-vs-join decision from sibling names alone.

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