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

Annotations already declare this a read-only, idempotent, non-destructive operation, so the safety profile is covered. The description adds genuine extra value beyond that: the specific validation rules applied and the dual success/error return shape (normalized IBAN, country, BBAN, or machine-readable error codes).

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?

Three tight sentences, front-loaded with the operation and checks, then the return shape, then the usage cue. No redundant or filler text.

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 validation tool with no output schema, the description covers what is validated, the accepted input (implied by schema), and the return payload including error codes. Nothing an agent needs to invoke 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 schema already documents the single 'value' parameter with an example and 'spaces allowed' note. The description only clarifies that the value is an International Bank Account Number, adding little beyond the schema, so the baseline 3 is appropriate.

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) and resource (IBAN), and enumerates the actual checks performed: mod-97 checksum, per-country length, SEPA membership. This clearly distinguishes it from siblings like validate_bic, validate_ein, and the VAT validators.

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 a concrete use context ('before paying an invoice or saving supplier bank details'), which is clear guidance. It does not, however, name alternatives or exclusions (e.g., 'use validate_bic for the BIC counterpart'), so it stops short of full routing guidance.

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