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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the bar is lower, yet the description adds real behavior: the 39-week week-by-week output structure, the two-tier rate formula, uprating switchover rules, and data provenance (gov.uk, fetched 2026-11-02). It does not say what happens when the employee fails the 26-week service or LEL test — error, zero pay, or a flag — which is the main remaining behavioral gap.

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 the core calculation and the rate structure, with no filler sentences; the provenance note is short and earns its place. It is dense and long-ish, but every clause carries substantive 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?

For a 4-parameter, no-output-schema tool, the description adequately conveys the return shape (week-by-week over 39 weeks) and the statutory logic. The only shortfall is unspecified behavior for ineligible inputs, which an agent would need to interpret results 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 all four parameters are already documented, including the smp_start_date default of the due date. The description explains derived concepts (qualifying week, LEL) but adds no format or constraint 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?

States a specific verb and resource ('Works out UK Statutory Maternity Pay week by week for 39 weeks') and immediately scopes the calculation model. It is clearly distinct from the siblings (sick pay, eligibility check, minimum wage rates), so an agent can select it without opening the schema.

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 calculation description, and the note that 'Same structure applies to Statutory Adoption Pay' hints at a related case. However, there is no explicit when-to-use guidance or routing versus check_eligibility, which overlaps with the qualifying-week and lower-earnings-limit facts this tool computes.

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