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

Annotations already declare this a read-only, idempotent, non-destructive, closed-world operation, so the description needn't restate safety. It adds genuine behavioral context beyond that: the check is format-only, no existence lookup is performed, test BICs are flagged, and "Nothing is stored" clarifies the no-side-effect contract.

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?

Four short sentences, capability first, limitations and side-effect guarantee last. Every sentence carries distinct information and there is no filler or redundancy.

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 does the work of describing the return content: parsed components, both code lengths, and a test-BIC flag. The one gap is that it never says how a failed validation is surfaced (error versus a valid=false result), which an agent would want to know before calling.

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 description coverage is 0% for the single `bic` parameter, so the description must compensate. It implies the input is a BIC/SWIFT string and that both 8- and 11-character forms are understood, which is some help, but it never states accepted casing, whitespace handling, or what happens with an invalid-length input despite the schema allowing up to 32 characters.

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?

"Validate a BIC / SWIFT code" gives a specific verb and resource, and the following sentences enumerate exactly what validation covers (shape, ISO country, decomposition into institution/country/location/branch). Nothing about the scope is left ambiguous, and it is clearly distinguishable from sibling validators like validate_iban or validate_routing_number.

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 line "Format only: it does not say whether the bank exists" is an explicit boundary that tells an agent when this tool is insufficient, which is real usage guidance. It stops short of naming an alternative for bank-existence lookups or of stating any other preconditions, so it does not reach the full when/when-not/alternatives bar.

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