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

The annotations already declare readOnlyHint, idempotentHint, and destructiveHint, covering the safety profile. The description adds the word 'exactly', implying precise arithmetic rather than approximations, which is useful behavioral context. However, it does not mention output format, edge cases, or error handling beyond what the schema notes (division by zero). Given the annotations, this is adequate but not rich.

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 a single, concise sentence that immediately states the core function and even includes a clarifying word 'exactly'. There is no fluff or irrelevant information, and it is appropriately sized for a straightforward calculator tool.

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 calculator with fully documented parameters, the description covers the essential operation. The lack of output format is not critical given the tool's nature, and error handling is partially covered by the schema. The mention of 'HelpySelf' is extraneous but not harmful. Overall, an agent has enough information to call this tool 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?

The schema provides 100% description coverage for all three parameters, including allowed forms (fractions, mixed numbers, whole numbers) and the operator enum. The description adds no additional parameter information, so the baseline of 3 is appropriate since the schema carries the semantic load.

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 explicitly states the tool performs addition, subtraction, multiplication, and division on fractions, with a clear verb and resource. It is distinct from the many other calculator tools in the sibling list because it is specifically for fraction arithmetic, so an agent can immediately identify its purpose.

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?

No explicit guidance is given about when to use this tool versus other calculators. The name and description make it obvious for fraction operations, but there is no mention of alternatives or exclusion criteria, leaving the agent to infer usage context.

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