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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the description is not burdened with those. It adds value by stating it's a 'cheap boolean check' and scoping to the 'calling user' and 'active player-recap page,' which are behavioral details beyond the schema. It does not mention error conditions, but given the simplicity and annotation coverage, this is acceptable.

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 with zero waste. The core purpose and return shape are front-loaded in the first sentence, and the usage guidance in the second. Every word earns its place.

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 simple existence check with one well-documented parameter, annotations covering safety, and an output schema hinted in the description, nothing essential is missing. The description covers the return value, scope, and intended usage context.

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% for sessionId, so the schema fully documents the parameter. The description does not add any extra semantics beyond what the schema provides, thus the baseline score of 3 is appropriate.

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 clearly states a specific verb (check) and resource (recap existence) with a precise return contract ({ exists: boolean }). It differentiates itself from siblings like play_create_page by focusing on the read-only existence check, leaving no ambiguity about its function.

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?

Explicitly instructs when to use it: 'Use this to gate play_create_page so you don't write a duplicate recap.' This names the alternative tool and the condition that selects this check, providing direct and unambiguous guidance.

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