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 contributes beyond that by disclosing the fixed count (26), the category ordering, and that rounds carry UTC open/close times and an answer-key hash — real payload context an agent cannot get from annotations.

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 sentences, front-loaded with the resource and its contents before the narrowing option. The parenthetical category list is somewhat long and closer to noise than signal, but it is cheap and does not bury the actionable instruction.

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 output schema and a single optional enum parameter, the description does the work of explaining what is returned: status per league and per-round times plus hash. An agent can call this correctly without further documentation.

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 100% and the enum already enumerates every valid league id, so the description need not document parameter values. It adds one behavioral nuance — that supplying league narrows the response to a single league rather than changing the shape — which is a modest increment over the baseline.

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 the resource (all 26 leagues) and the payload contents (each league's status plus rounds with open/close times and answer-key hash), so the agent knows exactly what it gets back. It does not name a sibling to distinguish against, which keeps it from a 5, but the purpose is unambiguous.

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?

"Pass league to get just one" gives the two modes of use (all vs. single), which is implied guidance. There is no statement of when to prefer this over related tools such as arena_leaderboard or arena_round_tasks, and no prerequisites or exclusions are given.

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