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

Annotations only cover readOnly/openWorld, but the description adds real behavioral semantics: the fatf_listing block is authoritative, a not_listed result is a positive determination rather than missing data, the coarse fatf field is a separate weaker signal, and currency is country-level and must not be used to diagnose account mismatches. These are non-obvious disclosure traits that go well beyond the annotations.

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?

Well front-loaded with the core purpose and return contents first, then scoping/warning notes, then examples. Every section is substantive, though the total length is on the heavy side for a one-parameter lookup, with some output-interpretation material that could be trimmed.

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?

An output schema exists so return values need not be explained, yet the description still clarifies the interpretation of key fields (fatf_listing vs. fatf, currency). Combined with readOnly annotations and a trivial single-param schema, an agent has everything needed to select and call this correctly.

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?

With a single parameter fully documented in the schema (ISO 3166-1 alpha-2), the schema does the heavy lifting. The description adds marginal value through concrete invocations that illustrate what different codes yield ("KZ" includes KNP, "AE" includes Purpose of Payment), reinforcing the parameter's role beyond the schema's generic example.

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 ("Get banking rules and requirements for a country") and enumerates exactly what comes back: IBAN requirements, SEPA membership, FATF status, national currency, account formats, payment requirements. It also explicitly distinguishes itself from the sibling country_payment_codes, so an agent can route without opening either schema.

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 explicit when-to-use ("check country-specific STP rules that could cause payment delays, repairs, or rejections"), an explicit alternative for code lookup ("Use country_payment_codes to look up specific code values"), and an explicit substitution instruction for FATF questions ("Use it instead of training data"). It also includes a when-not usage warning about pairing currency with the payment currency.

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