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

Annotations already establish readOnlyHint=true and openWorldHint=false, consistent with a pure computation, and the description adds that expected score is also returned alongside the three outcome deltas. It does not disclose rounding behavior, the default K of 20, or output structure, so it adds moderate value beyond 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?

Two sentences, front-loaded with the primary purpose and followed by the secondary return value (expected score). No filler or repetition of the name/title.

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 three-parameter calculator with no output schema, the description states both what is computed and what is returned (win/draw/loss deltas plus expected score), which is the key missing piece. Only minor items like rounding and default K are absent, and K is covered by the 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?

Schema coverage is 100% and the K-factor guidance (FIDE 40/20/10 tiers) is already in the schema, so the schema carries the parameter burden. The description mentions only "rating" and "opponent" implicitly and adds nothing about K-factor or valid rating ranges — baseline 3.

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?

"Calculates how many rating points a player wins or loses for a win, draw and loss" is a specific verb plus a precisely-scoped output, and it names the method (Elo formula). It does not explicitly contrast with siblings rating_meaning or recent_games, but the calculation/result nature is unmistakable.

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?

There is no when-to-use guidance, no mention of the alternative sibling tools, and no statement of preconditions (e.g., that it is a pure offline computation needing no game history). The agent must infer usage entirely from the purpose sentence.

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