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

Annotations already cover the safety profile (readOnly, idempotent, openWorld), but the description adds genuinely useful non-obvious behavior: pricing, the x402 payment flow, and that the call returns payment requirements rather than results unless payment_signature is supplied. It still omits what a successful verification returns.

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 tag and core purpose, followed by usage, pricing, payment behavior, and a sample pointer in a compact block. Dense but every sentence carries information; no filler.

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 covers purpose, usage, cost, payment mechanics, and a sample. It leaves the shape of a successful verification result (valid/invalid, matched company name) unspecified, which is a minor gap for a 2-param tool.

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%, so both parameters are already documented in the schema. The description restates the payment_signature behavior but adds no syntax or format detail beyond what the schema provides, making the baseline 3 appropriate.

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 ("Verify an EU trader's EORI number") plus the context in which it matters (shipping, invoicing, customs). It is clearly distinct from data-lookup siblings, though it does not explicitly contrast with the close sibling check_vat.

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?

"Use when customs paperwork or a shipment needs a confirmed EU EORI" gives a clear when-to-use trigger. It does not name exclusions or point to an alternative tool for non-EU VAT checks, so it falls short of full routing guidance.

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