Tarkista EU-ALV-tunnus (VIES)

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

Annotations already declare readOnlyHint=true, openWorldHint=true, and idempotentHint=true, covering safety and idempotency. The description adds context about the VIES service and the returned data (name and address), which goes beyond the annotations. It does not mention potential errors or latency, but that is not critical for a simple read-only check.

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 concise sentences. The first states purpose and output, the second gives usage and formatting examples. There is no fluff or repetition, and it is front-loaded with the most important 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 tool with a single parameter, no output schema, and strong annotations, the description covers the essential points: what it does, what it returns, and when to use it. Nothing critical is missing for an agent to invoke it 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?

The schema description covers 100% of the parameter with format examples, and the tool description reinforces this with explicit examples and the note about Finnish Y-tunnus. This adds clarity beyond the schema, though the schema already carries the main burden.

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 verb 'tarkistaa' (check) and the resource (EU VAT number via VIES), and specifies that it returns the registered name and address. It is distinct from sibling tools which cover other domains like procurement, company data, or weather.

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 an explicit usage scenario: 'Käytä ennen ALV 0 % -laskutusta EU-maahan' (use before VAT 0% invoicing to an EU country). It does not explicitly exclude other uses or name alternatives, but the sibling tools are clearly unrelated, so the guidance is sufficient.

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