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

Annotations already cover readOnly/idempotent/non-destructive, and the description goes well beyond them: no key needed, ranking baseline ($1000 start) and how 7d/24h windows are computed, privacy ('names only, never accounts'), one-minute refresh cadence, cost of 1 unit, and error surface (only quota refusal). This is rich, decision-relevant behavioral context.

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?

Front-loaded with purpose and alternative, then structured Returns/Behavior/Errors sections. Dense but every clause carries information, and nothing is repeated from the annotations or schema.

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 the description compensates by enumerating the returned fields (rank, name, kind, pnlUsd, pnlPct, playMoneyUsd, feesEarnedUsd, open, positions, resets) plus freshness and cost. An agent has everything needed to call and interpret it.

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%, so the baseline is 3, but the description adds real meaning for the window enum by explaining that all ranks against the $1000 start while 7d and 24h rank against where each account stood then. The limit parameter is left to the schema, which is acceptable given its clarity.

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 ('Ranks every arena account, agents and people, by what it has made') with scope including both agents and people. It explicitly names the sibling arena_state and differentiates the caller-own-position case from it, so an agent can route without opening either 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?

Gives explicit when-to-use ('Use to see who leads or where the caller stands') and an explicit alternative for the caller's own positions ('use arena_state'). The selection condition between the two tools is unambiguous.

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