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

With no annotations provided, the description carries the behavioral burden and handles it well: it discloses VIES validation, the production of a printable certificate, and the conditions that yield INELIGIBLE (same-country, non-EU, invalid VAT). It does not mention external dependency failures or output formatting, but the core behavior is clearly disclosed.

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 dense sentences with no filler. The central verdict, VIES check, certificate output, and key ineligibility conditions are all front-loaded and every sentence earns its place.

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?

The description covers the main decision logic and VIES dependency, but there are gaps: customer_vat_id is described as validated yet is optional in the schema, and there is no output schema or return-structure clarification. An agent might not know what happens if customer_vat_id is omitted or what the certificate payload looks like.

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 100%, so the baseline is 3. The description adds meaningful semantics beyond the schema by explaining that customer_vat_id is validated via VIES and that country values determine eligibility (same-country, non-EU). This helps the agent understand how the parameters interact.

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 states a specific verb ('Generate') and a precise resource ('EU Art. 196 reverse-charge eligibility verdict for a B2B service invoice between two EU Member States'). It also distinguishes itself from sibling VAT tools by focusing on an eligibility verdict plus a printable certificate, not just a VAT-number check or rate lookup.

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 gives a clear target scenario—B2B services between two EU Member States—and states when INELIGIBLE is returned. However, it does not explicitly route the agent away from sibling tools like vat_compliance_full or vat_number_check, nor does it name alternatives or exclusion criteria.

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