clients_vies_lookup

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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description adds value by saying what is returned (validity plus registered name/address) and that results come from an external system, but it does not disclose failure modes such as VIES being unavailable or unregistered numbers, which matter for an external lookup.

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?

Three short sentences, front-loaded with the action and followed by the return value and the use case. Nothing is redundant.

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?

With no output schema, the description correctly explains the return value (validity flag plus registered company details). It is nearly complete for a lookup tool; only external-service failure behavior is left implicit.

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%: vatCode format (country prefix, examples) and the companyId override are fully documented in the schema. The description adds no parameter-level information beyond that, 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?

States a specific verb and resource ('Validate a VAT code against the EU VIES system'), and the mention of EU VIES implicitly distinguishes it from the Romanian ANAF siblings (anaf_validate_cif, clients_anaf_lookup). It never names a sibling explicitly, so it stops short of full differentiation.

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?

Gives a concrete use case ('verify EU intra-community VAT numbers before applying reverse charge'), which tells the agent when this tool is appropriate. It does not state when to prefer clients_anaf_lookup or anaf_validate_cif instead, leaving the EU-vs-national choice to inference.

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