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

No annotations are present, so the description must disclose behavioral traits. It states the tool calculates and returns specific values, implying it is a read-only, side-effect-free operation. However, it does not explicitly confirm no data modification or highlight any permissions or rate limits. The description adds context beyond the schema but could be more comprehensive.

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: the first states the core purpose, and the second provides the return format and a reference to related tools. Every word is necessary and front-loaded. No redundant or extraneous information.

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 tool with three parameters fully described in the schema and a clear return format mentioned in the description, the description is complete. No output schema is provided, but the description lists the keys. The tool complexity is low, and the coverage is sufficient.

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?

All three parameters are clearly described in the input schema with descriptions, enums, and defaults. The description adds value by explaining the conversion between net and gross, which clarifies the 'mode' parameter's purpose. This goes beyond the schema's individual descriptions.

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 states the tool calculates UK VAT and converts between net and gross amounts. It specifies the return fields. While it mentions a related bundle to find other calculators, it does not explicitly differentiate from sibling VAT tools like 'calculate_vat_generic' or 'calculate_french_vat', but the UK-specific focus is clear.

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 provides no guidance on when to use this tool versus alternatives. It mentions 'See list_bundles for related calculators' but does not explain when to use this tool or when to avoid it. No conditions or exclusions are stated.

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