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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds genuinely new behavioral facts — no API key needed and 'Rate-limited' — but stops there: no indication of how limiting behaves or how results are ordered/paged.

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?

Purpose and the WHEN routing are front-loaded, and the fragment style keeps it dense. The 'Credit: Dead Brands' attribution is the one piece that doesn't help an agent invoke the tool, though it costs only a few tokens.

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 an output schema present, return values need no explanation, and the description covers auth, rate limiting, scope and sibling disambiguation. Only minor gaps remain around result ordering and whether the limit applies server-side.

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 100% with both parameters documented ('Optional game id filter', '1-50, default 20'), so the baseline applies. The description's example call uses an empty object and adds nothing about game or limit semantics beyond the schema.

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 ('Lists active arena matches for watching') plus scope ('public spectator list'). It explicitly positions itself against arena_list_matches (yours) and arena_spectate (one match), so an agent can pick it without opening any schema.

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 gives the trigger condition, '(no key)' gives the auth precondition, and the two named siblings define the selection rule — this is the list view, spectate is the single-match view. No alternative is left ambiguous among 80+ siblings.

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