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

With no annotations at all, the description carries the full behavioral burden, and it only partially discharges it: 'live' and the VIES reference usefully signal an external, real-time network call that can be slow or unavailable. It says nothing about what is returned (validity flag, company name, address), failure modes, or cost/rate behavior.

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?

A single front-loaded sentence with no filler; the core action and the data source come first and the format example is inline. It is efficient, though the brevity leaves the gaps noted in other dimensions.

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 zero annotations, no output schema, and an undocumented second parameter, the description is too thin: an agent cannot tell what the response contains or what 'verantwortlich' affects. The VIES reference and example ID are helpful but do not cover the tool's surface.

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 description coverage is 0%, so the description must compensate for both parameters. The embedded example 'LU26375245' is genuinely valuable for ust_id — it conveys the country-prefix format that the schema does not — but the second parameter 'verantwortlich' is never mentioned or explained anywhere.

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 names a specific verb and resource ('Prüft eine EU-USt-IdNr.') and adds the delivery channel ('live über die VIES-Schnittstelle der EU-Kommission'), so the agent knows exactly what operation this performs. It does not explicitly differentiate itself from the sibling tools (ki_hinweis, pflichten, rechnung_vorpruefen, werbung_vorpruefen), but the VAT-validation resource is obviously disjoint from them.

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?

There is no explicit when-to-use or when-not guidance, and no mention of alternatives or prerequisites (e.g. use before issuing an invoice, or what to do when VIES is down). The usage is only inferable from the verb 'prüfen' — an agent gets a hint of intent but no routing guidance.

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