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

With annotations already marking the operation read-only and idempotent, the description adds substantive behavioral detail: the exact thresholds (£12,570, £50,270), rates (8%, 2%), and the output breakdown (per year/month/week plus effective rate). It does not discuss edge cases like salaries below the threshold or rounding, but the disclosed formula is strong context.

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?

The description is three sentences, front-loaded with the purpose, followed by the calculation specifics and output summary. Every clause adds information, and the source URL is a compact optional addition.

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?

The tool is a simple one-parameter calculation with a rich annotation set and an output schema. The description covers purpose, tax year, formula, output granularity, currency, and source, so an agent has everything needed to call it 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?

The schema already documents the single `salary` parameter as 'Annual gross salary in GBP' (100% coverage). The description echoes 'annual gross salary' and 'Amounts in GBP' but adds no new parameter-level meaning, so the baseline of 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 opens with a specific verb and resource: 'Work out UK employee Class 1 National Insurance...' It also specifies the tax year, thresholds, rates, and outputs, which clearly distinguishes it from dozens of sibling calculators such as hopi_take_home_pay_calculator or hopi_net_to_gross.

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 identifies the exact scenario—UK employee Class 1 NI for 2026/27 from annual gross salary—so an agent knows when to invoke it. It does not explicitly name alternatives or exclusions, such as other NI classes or other tax years, but the narrow scope leaves little ambiguity.

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