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 covered. The description adds genuinely useful behavior: PRSI band and rate are resolved for the supplied date, and margin only appears when charge_rate is provided. It does not describe output shape or rounding, but that is minor given the annotations.

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?

One dense sentence, front-loaded with the tool's purpose and then the components, with essentially no filler. It is slightly long and comma-heavy, but every clause maps to a real input or output component.

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 7 parameters, 2 required, full schema coverage and annotations present, the description covers the full component set including date-sensitive PRSI and the conditional CWPS and margin paths. It leaves some minor gaps such as output breakdown and hours_per_week bounds (partly handled in the schema), but nothing that would cause a wrong invocation.

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 every parameter is already documented with defaults (date defaults today, auto_enrolment true, holiday_accrual_pct 12.35, CWPS false). The description restates the component list but adds no format, units, or edge-case detail beyond the schema, so 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 ('work out what a temp or agency worker really costs') plus the resource (employer cost in Ireland), and enumerates the exact cost components: pay, holiday accrual, employer PRSI, MyFutureFund auto-enrolment, CWPS, and margin. It is clearly a cost calculator, distinguishable from siblings like public_holiday_pay_ireland or irish_public_holidays.

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 discloses when optional components apply ('optional construction CWPS', 'the margin if a client charge rate is given'), which tells the agent the conditional inputs. It does not name alternative sibling tools or state when not to use this one, so it falls 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.