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

Annotations already establish read-only, idempotent, closed-world behaviour, so the description's job is domain context — and it delivers the calculation rule (5.6 weeks), the statutory cap (28 days), and the important caveat that the figure may include bank holidays. It doesn't mention rounding or that this is the statutory minimum rather than contractual entitlement, which would have pushed it to a 5.

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?

A single front-loaded sentence that leads with the output ('in days') and packs the jurisdiction, the 5.6-week rule, the 28-day cap and the bank-holiday caveat without a wasted word.

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?

An output schema exists, so return values need not be explained, and both required parameters are fully described in the schema. The description supplies the legal basis and caveats an agent needs to interpret the result correctly, leaving nothing material missing for a two-parameter calculator.

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% and both parameters are documented (nation as an enum of the four UK nations, daysPerWeek with 0.5–7 bounds). The description echoes 'set number of days a week' and 'any UK nation' but adds no syntax or edge-case guidance beyond the schema, so the 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: 'Work out the statutory minimum paid holiday a year, in days,' scoped to a worker's days-per-week and UK nation. It is clearly distinct from siblings like check_minimum_wage or check_deposit_cap, though it never names or contrasts them explicitly.

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 only implied by the domain framing ('for a worker who works a set number of days a week'). There is no statement of when to reach for this versus another check, no prerequisites, and no exclusions (e.g. self-employed, part-year workers).

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