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

Annotations declare readOnlyHint and openWorldHint, and the description is consistent with both while adding real context: which external registers are queried, what is checked (name match, VAT registration, active status, RO e-Factura), and that the IBAN and x402 payout wallet are surfaced. It also discloses that the tool returns actionable warnings, which the annotations do not convey. It does not state rate limits, failure modes, or how warnings are structured.

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 trigger ('Before paying'), followed by a dense but purposeful enumeration of what is verified. The long parenthetical and clause list make the first sentence run-on, but essentially every clause carries information an agent needs.

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 carries the return-value burden and does so at a summary level ('Returns warnings to act on') while enumerating the checks performed. A caller knows what it will learn, though the shape of the warnings and behavior on lookup failure are unspecified.

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% for the single 'invoice' parameter, so the schema already documents that it accepts a public token UUID or Billify link. The description adds no format or usage detail about the parameter beyond what the schema provides, 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 (check/verify) against a specific resource (the seller of an invoice) and names the exact registers consulted (ANAF for Romanian CUIs, VIES for EU VAT). An agent can tell this apart from get_invoice and pay_invoice without opening either schema, since it is explicitly a pre-payment verification step.

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 opening 'Before paying:' gives an explicit trigger condition that clearly separates it from the pay_invoice sibling. It does not name the siblings as alternatives or state when not to use it, so it stops short of a full when/when-not statement.

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