tax.vat

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

With no annotations, the description fully discloses behavior: real-time validation, coverage limits, returned fields (with conditional name/address), and the return object structure. This provides an agent with complete understanding of the tool's effects and data returned.

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 concise with three sentences, each serving a distinct purpose: purpose, coverage, and input/output details. Information is front-loaded, no redundancy, and 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?

Given the tool's simplicity and lack of output schema, the description covers all necessary context: input options, coverage, return fields, and real-time nature. An agent has sufficient information to invoke the tool correctly.

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 baseline is 3. The description adds value by clarifying the input options: 'Pass vat (full identifier like DE811569869) OR country + number.' It also provides an example and explains the combinatorial constraint, which is not explicit in the schema.

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's purpose: 'Validate an EU VAT number against the official VIES register in real time.' It specifies the resource (EU VAT numbers) and action (validation), and the surrounding siblings are unrelated, so it effectively distinguishes itself.

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 clear context on when to use (EU VAT validation) and includes coverage details (27 EU states + Northern Ireland, excludes Great Britain). It also explains the two input methods. However, it does not explicitly state when not to use or mention alternatives, though none are present among siblings.

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