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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world), yet the description still adds substantial behavior: tri-state results including a 'not checkable' outcome, the qualifying-week rule for the 26-week test, the 2026 SSP changes, the applicable lower earnings limits, and data provenance with a fetch date.

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?

Front-loaded with purpose and return shape, and the dense rule detail (dates, thresholds, SSP 2026 changes) is genuinely useful context rather than filler. It runs long as a single sprawling sentence and could be split for scanability.

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 an 8-parameter tool with no output schema, the description does the necessary work: it names the decision output, the rule set applied, and the data vintage. The return value is only loosely characterized ('the weekly amounts'), leaving the agent to infer exact fields.

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 coverage is 100%, so baseline is 3; the description earns above that by explaining the logic behind key inputs — the 26 weeks into the qualifying week for employment_start and due_date, and the LEL threshold applied to average_weekly_earnings. It still doesn't clarify what the returned 'weekly amounts' are relative to.

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?

States a specific verb (checks qualifying conditions) and a precisely scoped resource (five named UK statutory pay types), and describes the return shape (per-condition tri-state plus weekly amounts). This is clearly distinguishable from the calculate_* siblings, which compute amounts rather than eligibility.

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 makes the eligibility-checking purpose clear but never says when to prefer this over calculate_statutory_sick_pay or calculate_statutory_maternity_pay, even though it also returns weekly amounts, which creates overlap ambiguity. Usage is implied by the payment_type enum rather than stated.

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