List VAT rates

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

Declares 'Read-only and cheap' which aligns with annotation readOnlyHint=true. Adds contextual insight: rates change over time and differ per account, justifying read-only nature.

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?

Two concise sentences in first paragraph for purpose, then usage instructions. No fluff, every sentence adds value.

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?

Despite no output schema, description specifies output format (name/percentage pairs). Also provides usage context and caveats, making it complete for a listing tool.

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% with a description for companyVatCode. Description doesn't add new meaning beyond schema, so baseline of 3 is appropriate.

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?

Description explicitly states verb 'list', resource 'VAT rates', and output format 'name/percentage pairs'. Distinguishes from sibling tools by specifying its purpose.

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?

Explicitly instructs to call before create_invoice or create_estimate when uncertain about rates, and to copy returned values verbatim. Also warns against using remembered values due to variation.

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