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

With readOnlyHint=true already covering safety, the description adds substantial behavioral context: it reports what the opponent would play, explains that `considering` returns the refutation line, and warns that losing moves usually fall outside top candidates. This is exactly the kind of non-obvious behavior an agent needs, and nothing here contradicts the annotations.

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?

Three dense sentences, front-loaded with the main purpose and ending with the actionable `considering` use case. The 'quiet and merely looking quiet' phrasing adds color and some explanatory value, but is slightly more ornamental than strictly necessary.

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 tool with no output schema, the description covers return values well: candidate moves, scores, checkable facts, opponent reply, and refutation lines. It omits a few correctness details—there is no explicit statement that exactly one of fen/pgn/moves is needed despite zero required parameters, and engine score units/format are not described.

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 goes beyond the schema by linking the three position input parameters as alternatives and by explaining the non-obvious meaning of `considering` (returning the refutation line, not just an evaluation). Minor parameter semantics like multipv interaction and score format are left to the schema/defaults.

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 leads with a specific verb and resource—'Returns an engine evaluation of a chess position'—and enumerates exact outputs: candidate moves, scores, side to move, check status, undefended pieces, and material balance. It is not a tautology and clearly surpasses the generic title, but it never names or contrasts the sibling tools, so explicit sibling differentiation is missing.

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?

It gives concrete input guidance ('Accepts a FEN, a PGN, or a list of SAN moves') and a targeted use case for `considering`, even explaining when asking directly is the only way to expose a losing move. However, it never states when to prefer this tool over chess_attacks/chess_review or when not to use it, leaving alternative selection implied rather than explicit.

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