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

Annotations already declare readOnlyHint, idempotentHint, and closed-world, so the safety profile is covered. The description usefully adds that one value is solved for and that ratios can be reduced, but does not state how the missing value is chosen or which of A/B/C/D is optional.

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?

Front-loaded with the core operation and a concrete example in two tight clauses. The trailing web-page URL is extraneous filler but minor.

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 worked example (16:9) conveys the return format, and both modes are named. Adequate for a 5-param calculator, though it could clarify how an omitted value (all params optional) is handled.

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% but the parameter descriptions are bare letters ('A','B','C','D'). The description supplies the crucial A:B = C:D relationship that gives those letters meaning, adding real value over the schema, though it doesn't map each letter to its role explicitly.

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 specific verbs (solve, reduce) and the exact resource/relationship A:B = C:D, with a worked example (1920:1080 → 16:9). An agent can distinguish it from fraction_calculator or percentage_calculator without opening any 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?

Offers use cases (recipes, screen sizes, map scales, mixes) that imply when it applies, but gives no explicit when-not guidance or alternatives for overlapping tools. The two modes are only surfaced in the schema enum, not routed in the description.

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