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

No annotations are supplied, so the description carries the full load and does so: it discloses the three possible outcomes (PASSED/FAILED/UNAVAILABLE), the accompanying reason code and evidence, the paid/free cost model with a per-IP daily quota shared across REST and MCP, that failed attempts consume quota, and that payment requires explicit approval. It also states the correct interpretation of an outage, which prevents a costly false negative.

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?

Front-loaded with the core action and return values before routing, outage interpretation, and cost. Despite its length, each sentence carries distinct operational information (outcomes, alternatives, retry prohibition, quota, pricing) with no restatement of the tool name.

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?

There is no output schema, yet the description enumerates the return statuses, the reason code, and the evidence fields, so an agent knows what comes back. Combined with quota, pricing, and failure-interpretation notes, nothing needed to call or interpret this tool is missing.

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% and the single vat_number parameter is already documented with the IE-prefix, whitespace and lowercase normalization rules. The description adds nothing about the parameter beyond the schema, so this sits at the baseline for fully documented schemas.

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 chain (validates format and check letter, then confirms registration live with EU VIES) and the exact resource, which is more than the bare name conveys. It also distinguishes itself from check_company, verify_supplier_payment and decide_supplier_payment by naming what each of those does instead.

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?

Explicit scope boundary for use ('for one VAT number, not company-name matching or invoice approval') plus an explicit routing table to the three sibling alternatives. It also gives situational guidance for the outage case ('an outage is uncertainty, not invalid registration; do not auto-pay to retry'), which is exactly the kind of when-not guidance that prevents agent mistakes.

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