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

Annotations already mark the tool as read-only, idempotent, and non-destructive. The description adds useful context by stating the default UK rate and what the tool returns (net, VAT, and gross figures), going beyond the annotations without contradicting them.

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 concise sentences with no filler. The core operation is front-loaded, the default behavior is stated, the return figures are summarized, and the source is included without bloating the text.

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?

Given the simple calculator nature, strong schema with a mode enum, comprehensive annotations, and an output schema, the description covers everything an agent needs: purpose, modes, default rate, and returned figures. No meaningful gap remains.

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?

Schema coverage is 100%, so the baseline is 3, but the description adds meaningful operational context: it explains how 'amount' and 'mode' interact (net vs gross input) and confirms the default rate. This helps the agent map intent to parameters beyond the schema's basic 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 uses specific verbs ('Add UK VAT', 'remove VAT') and identifies the exact resource (a UK VAT calculator). It clearly differentiates the two operating modes and states the default rate, making it unambiguous among the large sibling list.

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 clearly explains when to use the tool: when you need to add VAT to a net amount or remove it from a gross amount. It does not explicitly name alternatives or exclusion scenarios, but the context is strong enough for an agent to select it correctly.

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