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

Goes well beyond the readOnly/idempotent annotations by disclosing that validation happens in memory and data is never stored, the plan requirement (Basic+ or limited free tier with verified account, 10 IBANs), and the billing semantics (each IBAN counts as one request). These are the behavioral facts an agent needs to decide whether to call.

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 purpose and batch limit, then return shape, then routing guidance, then constraints. Every sentence carries distinct information; nothing is padding or redundant with structured fields except the item cap, which is brief.

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?

No output schema exists, yet the description fully specifies the response shape (count, valid_count, invalid_count, results aligned to input order, each entry like a validate_iban result). Combined with the check types, storage posture, and access requirements, nothing needed to call it correctly is missing.

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 100% and the single parameter is fully documented (case-insensitivity, space tolerance, order preservation, 1–100 range). The description's restatement of the 100-item cap and input-order guarantee adds no meaning beyond the schema, so the baseline 3 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 (validate), resource (IBANs), and scope (batch of up to 100 in one call), and explicitly ties the semantics to the sibling `validate_iban` by name. An agent can distinguish it from `validate_iban` and the extract/lookup siblings without opening any 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?

Explicitly instructs to use this instead of calling `validate_iban` in a loop when checking a list, gives concrete examples (payment file, supplier accounts column), and states the alternative behavior for oversized inputs (>100 → split into multiple calls). Both when-to-use and when-not are covered.

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