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

Annotations already cover safety (readOnlyHint, idempotentHint, openWorldHint), so the bar is lower. The description adds real value beyond them by explicitly bounding what the result does NOT prove — account ownership, beneficiary identity, fraud absence — which is critical for an agent deciding how much to trust a positive result.

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 sentences, zero waste, with the positive capability front-loaded and the limitation following. Every clause earns its place.

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?

An output schema exists, so return values need not be explained here. Combined with the scope disclaimer and a single fully documented parameter, the definition is essentially complete for a stateless validator; only explicit sibling routing 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?

Only one parameter and schema description coverage is 100% ('IBAN to validate; spaces allowed.'), so the schema fully documents the input. The description adds no syntax, formatting, or length details beyond the schema, making the baseline 3 correct.

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 ('Validate IBAN structure and MOD-97 checksum'), which immediately distinguishes it from siblings like swift_bic_check, gstin_check, and vat_mod97_check. The scope is narrow and unambiguous.

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?

Usage is implied by the purpose — call it when you need IBAN format/checksum validation — but there is no explicit when-to-use guidance or routing against siblings such as vat_mod97_check or batch_validate. The second sentence is a scope disclaimer, not invocation guidance, so this is minimum viable rather than strong.

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