Validate UK VAT Number (HMRC)

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

Annotations already declare readOnlyHint, idempotentHint, etc. The description adds useful behavioral context: returns trading name and address, and notes that the VAT address often differs from Companies House address as a due diligence signal. This goes beyond what annotations provide.

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?

Concise, well-structured, with no unnecessary words. Three short paragraphs: purpose, output, and scope limitation. 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?

For a single-parameter tool with high schema coverage and an output schema (not shown but present), the description fully explains the tool's purpose, output, and limitations. No gaps remain.

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% and the schema description already explains format and normalization. The description adds context about what the parameter is used for and what the tool returns, but does not add strictly new parameter semantics. A 4 is appropriate for the added contextual value.

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?

Describes exactly what the tool does: validate a UK VAT number against the HMRC register. The verb 'validate' and resource 'UK VAT number (HMRC)' are specific. It is clearly distinct from sibling tools like company_search or sanctions_screen.

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 states UK numbers only and directs users to the EU VIES service for non-UK numbers. Provides clear when-to-use and when-not-to-use guidance.

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