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

No annotations are provided, so the description must bear the full burden. It states the return fields and tax year but lacks details on side effects, authentication needs, or whether the operation is read-only. It does not contradict annotations as none exist.

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 two sentences long, front-loading the core purpose and return structure without unnecessary detail. It effectively points to related tools in a concise manner.

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?

For a simple calculator with one parameter, the description adequately covers functionality and directs to related tools. It lists return fields directly, compensating for the lack of an output schema. Minor omission: does not specify that calculations assume standard rates for the given year.

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 input schema covers the one parameter (annual_salary) with a description already specifying GBP. The tool description adds no further semantic meaning beyond what the schema provides, achieving the baseline of 3 given 100% schema 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?

The description clearly specifies the tool calculates UK National Insurance contributions for Class 1 employees for tax year 2025/26, using a specific verb and resource. It distinguishes itself from the many sibling calculator tools by naming the exact tax and year.

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 description mentions related calculators via 'See list_bundles' but does not explicitly state when to use this tool versus others, nor does it provide prerequisites, exclusions, or context about when not to use it (e.g., for self-employed NI).

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