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

Annotations already cover read-only, idempotent, closed-world semantics, so the description only needs to add what they don't. It does: the absence of a bank directory warns that a syntactically valid code may not map to a real institution, and the component breakdown previews the result since no output schema exists.

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?

Two short sentences, front-loaded with the verb and result, with the scope caveat last. Nothing is wasted, though the second sentence is a fragment that could have been folded in.

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, describing the four parsed components is exactly the right compensation, and the no-directory caveat sets expectations. It stops short of saying what happens on an invalid or malformed code, which is the main remaining gap for a checker 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?

There is a single parameter with full schema coverage ('SWIFT/BIC code, 8 or 11 characters'), so the schema carries the weight. The description adds no length, format or example detail beyond it, which is the expected baseline for a one-param tool.

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 concrete verb (check well-formedness) plus a parsing result (split into bank, country, location, branch), so the agent knows both the validation and decomposition behavior. The closing note 'Has no bank directory' differentiates it from directory-lookup-style validators and from siblings like iban_checker.

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 'Has no bank directory' line implies the scope (format-only, no existence check), which is useful routing information, but it never states explicitly when to choose this over iban_checker or lei_checker, nor what a failing check returns. Usage is inferable rather than spelled out.

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