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

Annotations already cover read-only, idempotent, closed-world and non-destructive, so the description is free to add genuinely new facts: the exact rate years held (2024–2027), the published future figures, and data provenance/currency ('fetched from gov.uk on 2026-11-02'). It does not spell out behaviour for dates outside the covered years, which is the main remaining ambiguity.

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?

Purpose and scope are front-loaded in the first clause, but the parenthetical enumerating specific figures (£12.71, £10.85, £8, £13.21, £11.27, £8.31) is payload data that belongs in the response, not the selection description. Those tokens cost attention without helping the agent decide whether to call the tool.

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 no output schema, the description carries the burden of describing returns, and it does: hourly rates per age band, apprentice rate, the applicable rate, and optional weekly/annual pay. Provenance is disclosed. The only gap is behaviour for a date outside the 2024–2027 coverage window.

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 the baseline is 3, but the description adds real meaning beyond the schema: it explains the age→band mapping outcome, that apprentice interacts with the age band, and that hours_per_week produces weekly and annual pay. That explains the result of combining parameters rather than restating field definitions.

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 ('Returns the UK National Living Wage and National Minimum Wage hourly rates') plus scope qualifiers: in-force-on-a-date, by age band, apprentice rate, and the applicable rate for a given age. It also names the secondary output (weekly/annual pay at the rate), which clearly separates it from the statutory-pay calculator siblings.

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?

It makes the call conditions clear: supply a date to pick the in-force table, an age to get the applicable rate, and hours_per_week to get derived pay. It never names an alternative tool or an exclusion ('do not use for statutory sick/maternity pay'), so it stops short of explicit when-not guidance.

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