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

Annotations already declare readOnly, idempotent and non-destructive, and the description usefully pins the behavioral scope to Class 1 employee contributions for a single tax year, implicitly excluding employer NI and Class 2/4 self-employed cases. It does not mention assumptions such as the standard personal allowance or the Scotland-vs-rUK distinction, so it stops short of full disclosure.

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?

Three short, front-loaded sentences: purpose first, return shape second, cross-reference last. No filler, no restatement of the tool title.

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 enumerating the return keys is redundant but harmless, and the tax-year and contribution-class scoping is genuinely needed context. The definition is complete for a one-parameter deterministic calculator, though it omits which regional NI regime (e.g. Scotland) applies.

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?

Single parameter at 100% schema description coverage ('Annual gross salary in GBP'), so the schema carries parameter semantics fully. The description repeats the currency concept but adds no syntax, range, or unit nuance beyond the schema, matching the baseline 3 for high coverage.

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 with narrowing qualifiers: 'UK National Insurance contributions (Class 1 employee)' for tax year 2025/26. That scope alone separates it from the many sibling tax calculators like calculate_uk_income_tax and calculate_uk_student_loan without opening any 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?

The only routing guidance is 'See list_bundles for related finance-uk calculators,' which points to discovery rather than stating when this tool is the right choice. There is no explicit when-not or named alternative, so usage is implied by the domain scoping rather than spelled out.

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