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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds only 'Auth required', which is useful but partially inferable from the key parameter, and it says nothing about behavior on an invalid or expired key.

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 payload statement is front-loaded and the whole definition is two short sentences plus an example. The example call with empty braces earns its place by showing the optional-parameter usage, leaving little waste.

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 parameterless-by-default read tool with full annotations and an output schema, the description covers the payload and the auth requirement. Nothing critical for a correct call is missing, though error behavior on auth failure is 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?

The tool has a single optional parameter whose schema description already fully documents the key and the Authorization: Bearer alternative (100% coverage), so the baseline applies. The description adds no further meaning about the key beyond 'Auth required'.

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 names the resource and enumerates exactly what it returns: cosmetic inventory, equipped slots, and credit balance, which separates it from the write-side arena_cosmetics_equip. The verb 'read/get' is only implied by the 'My cosmetics' framing, so it is clear but not stated as a specific verb.

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 'WHEN:' clause supplies a usage trigger, but it largely restates the return payload rather than giving a decision rule against alternatives such as arena_cosmetics_equip or arena_shop_browse. No when-not guidance is offered.

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