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

With no annotations, the description carries the full behavioral burden, and it does disclose the single most important trait: the tool is not implemented and calling it records a requirement rather than performing a lookup. That is genuinely useful and prevents false assumptions about a real VIES call. It still omits what happens on invocation (error, stub response, storage of the VAT value) and any side effects or rate considerations.

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 short sentences, with the most decision-relevant fact ('Roadmap probe, not yet served') front-loaded before the domain description. No filler; the only minor weakness is that the second clause is terse to the point of being cryptic.

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 one-parameter stub with no output schema, the description covers the crucial 'not yet served' status. It is still incomplete about the observable result of a call and how the recorded requirement surfaces, which is what an agent needs to decide between this and request_data or find_capability.

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?

There is a single parameter with 100% schema description coverage, though the schema itself only repeats the field name 'vat'. The description adds no format guidance (country prefix, spacing, length expectations) beyond the schema, so the baseline 3 applies.

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 resource and capability (VIES VAT validation with provenance), which is more than a restatement of the name. However, it immediately undercuts that purpose with 'Roadmap probe, not yet served', leaving ambiguity about whether the tool validates VAT or merely logs intent. An agent can guess the domain but not the actual verb that will execute.

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?

'Calling records the requirement' hints at a demand-signal use, but there is no explicit when-to-use guidance, no exclusions, and no routing to alternatives. Siblings like find_capability and request_data plausibly cover the same 'express a need' role, and the description never differentiates.

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