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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds real value beyond that by enumerating the computed outputs, including employer NI saved and passed back and benefit-in-kind tax for a car, which an agent needs to know since no output schema exists. It stops short of stating currency, rounding, or assumptions about annual allowance limits.

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?

It is a single front-loaded sentence with the action stated first and zero filler. The long trailing enumeration of outputs makes it dense and run-on, which slightly hurts scanability, but 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 eight parameters and no output schema, the description correctly spends its budget enumerating what is returned, covering both the pension and EV-car branches. It is complete enough to call correctly, though it omits currency, precision, and any caveats about what the calculation ignores.

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 all eight parameters, making 3 the baseline. The description lightly connects parameters to outputs ('employer National Insurance saved and passed back' maps to employerNIPassback, 'benefit-in-kind tax for a car' maps to carP11dValue), but adds no syntax, defaults, or constraint detail beyond the schema.

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 opens with a specific verb and resource: 'Compare pay before and after a salary sacrifice for a pension or an electric company car,' and it scopes the two supported scheme types. What it lacks is explicit differentiation from siblings such as calculate_take_home_pay or calculate_pension_tax_relief, so an agent must infer which calculator to pick.

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 implied by the enumerated outputs (tax, NI, student loan, employer NI passback, BiK, take-home drop), which tells the agent this is the salary-sacrifice comparison tool. However, there is no explicit when-to-use/when-not statement and no named alternative for related questions like plain take-home pay or standalone pension relief.

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