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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds useful behavioral context beyond that: it specifies the outputs (yearly, monthly, weekly pay and fraction of full-time), the currency (GBP), and the tax treatment (gross before tax), which are all meaningful operational details.

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, each earning its place: the first explains the calculation, the second covers return values, units, and source. No filler, no repetition of schema content, and the key scoping information is front-loaded.

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 read-only calculator, this is complete. All three parameters are documented in the schema, the description explains the output (yearly/monthly/weekly pay and fraction), and it adds currency and tax context. The output schema exists, so the description needn't detail return structure. No material gaps remain for an agent 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?

Schema description coverage is 100%, so the baseline is 3. The description adds value by explaining how the parameters relate ('scaling a full-time salary by the ratio of your hours to full-time hours'), which clarifies the roles of fullTimeSalary, fullTimeHours, and hours. It also indicates the output granularity, though it does not restate individual parameter formats since the schema already does that.

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 states a specific verb and resource: 'Work out a pro rata salary for part-time hours by scaling a full-time salary'. It clearly differentiates from related sibling calculators (e.g., hourly_to_salary, day_rate_calculator) by focusing on the pro-rata fraction and the full-time to part-time ratio, leaving no ambiguity about what the tool computes.

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?

The description gives clear context for when to use the tool: when you have a full-time salary and part-time hours. It implies exclusions by noting 'gross before tax', which signals it is not for take-home pay calculations. However, it does not explicitly name alternatives like hopi_take_home_pay_calculator or hopi_hourly_to_salary, so it falls just short of a 5.

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