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

Goes well beyond the readOnly/idempotent annotations: it defines the data_confidence tiers (high = public check-digit spec, medium = community checksum/pattern, low = structure only) and states the crucial limitation that results are structural validation only, never proof of issuance or ownership. It also discloses the returned fields (checks performed, reason when invalid, extracted details).

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 purpose, then example, then response shape — a sensible order. It is dense and long for two parameters, and some response-field enumeration overlaps with the output schema, but no sentence is pure 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?

Since an output schema exists, the response summary is largely redundant, but the confidence-tier semantics and the disclaimer add meaning the schema cannot convey. Everything an agent needs to call it correctly is present; only the sibling-selection question is left open.

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 already 100%, and the description still adds value with a concrete worked example ('784-1990-1234567-1' with code 'ae_emirates_id'). It does not add anything about number normalisation beyond what the schema's tolerance note already covers, so it is above baseline but not materially so.

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?

Specific verb+resource ('Validate and normalise one identifier') with a clear scoping constraint, 'whose type you know', which implicitly separates it from detect_identifier. However, the overlap with type-specific siblings (validate_iban, validate_bic, validate_phone, validate_postal_code) is never addressed, so which tool to pick for an IBAN remains ambiguous.

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 phrase 'whose type you know' gives a clear usage condition and implicitly routes unknown-type cases to detect_identifier. It stops short of naming that alternative explicitly, and gives no guidance on when to prefer a dedicated validator (validate_iban) over this general one.

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