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

Annotations already cover the safety profile (read-only, idempotent, closed-world), so the description is free to add value — and it does: a hard 25-second deadline for the entire analysis and an explicit scope limit ('no cheating verdict'). Those are behavioral facts not derivable from the annotations or schema. Depth/cost trade-offs under that deadline are left unstated.

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?

One dense sentence front-loads the action, scope, engine, and outputs, with the operational constraint and disclaimer trailing. No filler; every clause carries information.

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 read-only analysis tool with no output schema, the description covers input shape, engine, metrics, and a critical time constraint. Missing: what the response looks like (per-position vs aggregate agreement/CPL) and how depth interacts with the deadline.

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 0%, so the description must compensate: it does explain the positions array semantics (FEN + played moves, 4–40 count), which is the meaningful parameter. The depth parameter (4–20, default 12) and its accuracy/latency trade-off under the 25s deadline are never mentioned.

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 (Compare) applied to a precisely-scoped resource (4–40 FEN positions with played SAN/UCI moves) using a named engine (Stockfish), yielding two named metrics. No sibling in the list does anything comparable, and an agent can distinguish it without inspecting the 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?

Implies the input shape (supplied positions/moves) and the engine used, but says nothing about when to prefer this over alternatives or what conditions make it inapplicable. The 'no cheating verdict' note hints at a boundary but is framed as an output disclaimer rather than a use condition.

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