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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered by structured data. The description adds a little beyond that by implying the return set (expected score plus deltas for win/draw/loss) for a pure calculation, but it does not spell out the return shape despite there being no output schema.

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?

A single dense sentence with the computation and its inputs front-loaded and 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 simple pure-function calculator with three parameters and full annotation coverage, the description conveys the inputs and the intended outputs. The only gap is the precise return structure (how the win/draw/loss deltas are presented), which matters slightly since no output schema exists.

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 33%: only k_factor is documented in-schema (with useful FIDE defaults), while rating and opponent_rating rely on self-explanatory names. The description reinforces that both inputs are Elo ratings and that the K-factor is a deliberate choice with a default, but it adds no units, ranges, or validation behavior beyond the schema.

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 names the exact computation: expected score and rating change for a win, draw or loss between two Elo ratings, parameterized by K-factor. This is a specific verb+resource statement an agent can match to an intent. It does not explicitly distinguish itself from the sibling fide_rating, which is the nearest potential confusion (official rating lookup vs. hypothetical delta calculation).

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?

Usage is implied by the framing — this tool is for hypothetical 'what would happen if' questions about a match outcome between two ratings. There is no explicit when-to-use vs. when-to-use-something-else guidance and no exclusions (e.g., 'not for looking up official ratings, use fide_rating').

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