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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered; the description adds that the payload is a supported-value catalog and that one field is deliberately free text. It stops short of noting whether the values are static or fetched live, which the openWorldHint implies but does not confirm.

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, zero filler: the first enumerates what comes back, the second states when to call it and the one caveat. The usage instruction is front-loaded relative to the caveat, so an agent reading only the opening clause still gets the right call pattern.

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 zero-parameter lookup with a full output schema and read-only annotations, nothing material is missing: what it returns, when to call it, and the open-text exception are all stated. Return-value detail is correctly delegated to the output schema.

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?

The tool takes zero parameters, so there is no parameter semantics for the description to carry; the baseline of 4 applies. No misleading hints about inputs are introduced.

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 ('Returns') plus the exact resources enumerated: difficulty, side-to-move, tablebase and cloud-evaluation variants, and the puzzle-batch size range. An agent can distinguish this metadata lookup from lichess_puzzle, lichess_tablebase, and lichess_cloud_eval 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?

Explicitly instructs 'Use these values before selecting enum inputs for puzzle, tablebase, or evaluation tools,' which gives both the timing and the target consumers. It also carves out an exception ('puzzle angle remains open text'), preventing a wasted lookup attempt.

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