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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description contributes one genuine extra fact — "No auth" — meaning the agent can call it before authenticating, plus the alias-mapping behavior that annotations can't express. It doesn't describe shape or size of the catalog, but an output schema exists so that burden is lifted.

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?

Three short fragments with the scope and the no-auth note front-loaded — nothing wasted. The telegraphic 'WHEN:' phrasing reads as a note-to-self rather than prose, which slightly hurts readability but not economy.

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?

With no parameters, an output schema, and full annotation coverage, the description only needs to explain what the catalog contains and any calling precondition; it does both ('unifies shop + prize shelf + bazaar cosmetic ids with aliases', 'No auth'). What's missing is how the aliases map onto ids used by downstream tools like arena_cosmetics_equip or arena_prize_redeem, though the output schema likely covers that.

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 there is nothing to disambiguate; the included example `arena_catalog {}` confirms the empty-argument invocation. Baseline of 4 applies for a zero-parameter tool.

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 a concrete resource and its scope: a single catalog that merges shop, prize-shelf and bazaar cosmetic ids along with their aliases. That distinguishes it from the sibling browse tools (arena_shop_browse, arena_prize_shelf, bazaar_shop_browse) which surface each catalog separately. It falls short of a 5 because there is no explicit verb ('unified catalog' restates the title) — the action is only implied by the content description.

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?

"WHEN: one prize/cosmetic catalog" signals the use case but is a fragment and never names the alternative call to make when you want a per-surface listing. It tells the agent the situation but not the exclusion, so the selection logic is implied rather than stated.

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