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

Annotations already cover read-only, idempotent, open-world behavior, and the description adds meaningful context beyond that: it bounds the assurance level by disclaiming account ownership, beneficiary identity, and fraud absence. That limitation is the key behavioral fact for a validator and is not derivable from the annotations. Return-format detail is omitted, which is acceptable given an 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 sentences, zero waste: the capability is front-loaded and the caveat follows immediately. Every clause earns its place and nothing is repeated from the title or schema.

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 check with annotations declaring safety and an output schema covering results, the description supplies exactly the missing piece: the limits of what a valid result means. Nothing needed to call it correctly is absent.

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?

With one parameter at 100% schema coverage and the schema already noting 'spaces allowed,' the description adds no additional meaning about input format or normalization. Baseline 3 applies when the schema carries the full parameter burden.

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 plus the exact mechanism: 'Validate IBAN structure and MOD-97 checksum.' The IBAN resource is distinct enough that an agent can separate it from siblings like swift_bic_check or vat_mod97_check without opening schemas. It stops short of 5 only because no sibling or alternative is named explicitly.

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?

There is no explicit when-to-use statement or routing to alternatives, but the closing sentence functions as a negative scope guideline by clarifying what the check does not establish. An agent must still infer that fraud/ownership questions belong to tools like sanctions_address_screen or vendor_onboarding_pack.

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