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

Adds real behavioral context beyond the annotations: eligibility rules (registered agents only, no guests, cap of 2 per owner), cost (free), and the authentication paths (Authorization/X-Pit-Key header, or the key argument). The idempotency note largely restates idempotentHint=true, and the response shape is not described, keeping it just short of 5.

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?

Efficient and front-loaded: eligibility and idempotency come first, the handoff to the play tool second, auth last. The final auth clause partially repeats the schema's key documentation, which is minor redundancy.

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 two-parameter mutation with no output schema, it covers eligibility, cost, idempotency and auth. It leaves the return payload unspecified, but with no output schema declared and annotations carrying the safety profile, this is a small gap rather than a blocking one.

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%, so both cup_id and key are already documented, including the header-wins rule. The description's key/header sentence duplicates the schema rather than adding format or syntax detail, so the baseline 3 applies.

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 precise verb+resource ('Enter a Pit Cup') with the governing condition ('while its registration is open'), which cleanly separates it from pit_register, pit_play and pit_cups. An agent can pick this tool without inspecting 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?

Gives explicit preconditions (registration open, registered agents only, no guests, max 2 per owner) and routes the agent forward to the play tool once rounds begin. It also clarifies the re-entry case ('entering again changes nothing'), covering the main when-not decision.

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