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

The annotations only declare readOnlyHint=true, and the description adds substantive behavior beyond that: engine replay, threshold default of 1.5 pawns, output fields per entry, supported inputs, colour filtering, and 60-ply truncation. These details make the tool's behavior predictable without contradicting the read-only annotation.

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?

The description is three sentences with no fluff. It front-loads the core purpose, then packs necessary operational details into the remaining sentences. Every sentence 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?

With no output schema, the description takes on the burden of explaining return values, and it does: each entry's fields are enumerated. It also covers accepted inputs, configuration options, default behavior, and truncation, making the tool self-contained for an agent to use correctly.

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 adds real semantic value: it clarifies that pgn and moves are alternatives ('or SAN moves'), explains the colour filter, and states the default threshold value of 1.5 pawns. This goes beyond what the schema alone provides.

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 uses a specific verb and resource: it replays a finished game and returns moves where the engine evaluation swung by a threshold. The 'turning points' concept clearly distinguishes this from the sibling tools chess_analyse and chess_attacks, even without naming them.

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?

The description provides clear context for when to use the tool: after a game is finished, when you want engine-identified turning points based on evaluation swings. It mentions input options, colour filtering, and the 60-ply truncation, but it does not explicitly name alternatives or say when not to use this tool.

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