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

Annotations already declare readOnlyHint, openWorldHint=false, and idempotentHint, so the safety profile is known. The description adds useful behavioral context beyond that: it returns a checksum result and a normalized form where applicable, and it explicitly stores and looks up nothing and requires no API key or account. It does not describe the response shape, but that is a minor gap for a simple validator.

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 tightly written sentences with no filler. The supported types and the stateless, no-account behavior are front-loaded, and every clause contributes useful information.

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 two-parameter stateless validator with no output schema, the description covers the formats accepted, the checksum and normalization behavior, and the absence of storage or authentication requirements. Only the exact return format is unstated, which is a reasonable omission given that there is no output schema and the behavior is described in prose.

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 description coverage is 100%, and the schema already documents both the type enum and the value field including the tolerance for spaces and dashes. The description reinforces the supported formats and mentions normalized output, but it adds no syntax or format detail beyond what the schema already provides.

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?

The description gives a specific verb (validate) and enumerates the exact resource types it handles: IBAN, payment card via Luhn, Norwegian orgnr, kontonummer, and phone number. It also distinguishes itself from the sibling validate_email by listing only non-email formats, so an agent can select it without opening the 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?

Usage is implied by the list of supported value types, but there is no explicit when-to-use or when-not-to-use guidance and no named alternative such as validate_email. The statelessness note helps an agent understand it is safe to call, but the routing guidance is only indirect.

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