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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is fully covered without the description. The description adds one genuinely useful behavioral detail — that results are 'exact' and returned as simplified, mixed, and decimal forms — but since an output schema exists, this is modest added value.

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 well-formed sentence that front-loads the operation and resource before the output detail. There is no filler and 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?

With rich annotations, a fully documented 3-parameter schema, and an output schema covering return values, the description is nearly sufficient for an agent to call this correctly. Only the absence of any routing hint toward sibling tools keeps it from being complete.

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 description coverage is 100%, so the schema already documents a, b, and the operation enum with its default. The description adds nothing about accepted input syntax beyond what the schema's 'integer, fraction, decimal or signed mixed number' wording already provides; the baseline 3 applies.

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 gives a precise verb (computes) plus the exact resource and supported operand types (fractions and mixed numbers), and enumerates all four operations. It clearly separates this arithmetic tool from conversion siblings like decimal_to_fraction, though it never names an alternative explicitly, keeping it just short of a 5.

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 only implied by the tool's nature — an agent can infer 'use this to do fraction arithmetic' but the description states no conditions, prerequisites, or when-not-to-use guidance. No alternative tool (e.g., decimal_to_fraction, round_decimal) is mentioned for related tasks.

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