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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description still adds real value: the validation is offline against a bundled country table, output is normalised/formatted, and account existence is explicitly not verified.

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?

A single front-loaded sentence leading with the verb and resource, with each clause (length table, checksum, output form, BBAN, limitation) carrying distinct 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?

For a single-parameter, no-output-schema tool, the description covers the validation semantics, output normalisation, and the key limitation. It stops short of describing the actual return shape or failure behavior, but is largely sufficient.

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?

Only one parameter, and schema description coverage is 100% ('IBAN, spaces allowed'). The description adds nothing about the iban argument beyond the schema, so the baseline 3 for full schema coverage applies.

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 ('IBAN validation') and enumerates the exact checks performed (country length, mod-97 checksum, BBAN/check digits). An agent can distinguish it from siblings like se_validate or se_account_to_iban, though it never names or routes to them.

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 one explicit exclusion ('Does not check that the account exists'), which is genuinely useful scope-setting, but offers no when-to-use framing or alternatives (e.g. se_account_to_iban for conversion). Usage is implied rather than stated.

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