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

Annotations already declare readOnlyHint=true and openWorldHint=false, and the description adds real domain behaviour: Class 2 eligibility limited to years up to 2025–26, the 6 April 2026 rule change, fixed weekly rates, and the 35-year cap. It does not disclose edge-case handling or validation of out-of-range gap years, keeping it from 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?

It is a single long sentence, but it is front-loaded with the purpose and every clause (rates, deadlines, 1/35 accrual, payback) carries distinct information. Slightly denser than ideal to parse, but there is no filler.

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?

There is no output schema, and the description compensates by stating what the tool returns: per-year cost, 5 April deadline, pension gain (1/35 of £241.30/week, capped at 35 years), and payback. For a read-only calculator of this complexity, that is enough for an agent 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?

With 100% schema description coverage across all 7 parameters, the schema already carries the per-parameter meaning. The description explains the underlying rules (rates, caps, deadlines) but does not map them to specific inputs such as qualifyingYears or appliedBefore2026, 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?

The description names the exact resource (voluntary National Insurance gap years for UK State Pension for people living outside the UK) and its scope boundary (2020–21 to 2026–27, post-6 April 2026 rules). Nothing in the sibling list overlaps, so an agent can route to it unambiguously.

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 context is implied by the topic (living abroad with UK NI gaps), but there is no explicit when-to-use/when-not guidance and no named alternative for someone resident in the UK or for a different pension question. The agent must infer the trigger from the subject matter alone.

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