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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful context beyond that: the paid Bearer-key requirement with a pricing URL, that it assesses whichever identifiers are supplied, and the limits of what 'valid' means (internally consistent or plausible, not name-matched).

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?

One dense but well-ordered paragraph that front-loads the operation, then lists checks, then the caveat about what it is not, then the auth note. 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?

Seven optional parameters, no output schema, and the description covers purpose, coverage limits and auth well. The main remaining gap is the shape of the result — whether it returns per-identifier pass/fail and reasons — which an agent would want to know, though the absence of an output schema makes this a modest omission.

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 the baseline is 3, but the description adds meaning the schema does not: it explains what each identifier is actually checked against (own checksum, format standard, recognition against known major banks, country code plus length). It omits mention of the CLABE parameter that the schema documents, which slightly weakens coverage.

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 ('Structural check') and resource ('a payment destination') and enumerates exactly which identifiers are assessed and against which standards (ISO 7064 MOD 97-10, ABA checksum, ISO 9362, EIP-55, SA branch codes, SADC mobile money). It also draws an explicit boundary against confirm/verification of payee, so an agent can distinguish it from sibling payment tools.

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 clear use case ('before you send', catching the most common cause of a misdirected payment) and explicit exclusions (UK sort codes, most domestic account numbers, no name confirmation). It does not name a specific sibling to use instead when payee-name confirmation is what's needed, which keeps it short of a 5.

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