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

Annotations already declare readOnly/idempotent/openWorld=false, but the description adds meaningful context beyond them: nothing is stored or looked up, no API key/account/signup needed, and it returns the checksum plus normalized form where applicable. It stops short of describing failure/error behavior for invalid input.

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-loads the validated types, then the guarantees, then the call-to-action. Two efficient sentences; the trailing auth reassurance is slightly redundant but still useful for an agent deciding whether it can invoke without setup.

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 indicates what comes back (checksum and normalized form) and that there are no side effects, which is enough for a stateless validator. A brief note on invalid-input behavior would make it fully complete.

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 50%, but the description compensates by expanding the enum values into human-readable forms (e.g. 'payment card number (Luhn)', 'orgnr', 'kontonummer') and clarifies the value accepts spaces/dashes. It adds real meaning to the enum beyond the bare schema tokens.

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 precise verb (validate) and enumerates the exact resource set (IBAN, card/Luhn, orgnr, kontonummer, phone), with the checksum/normalized-form scope. An agent can distinguish this from validate_email immediately since email is not listed. No sibling overlap.

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?

Provides clear context that it is stateless and directly callable, and the enumerated types implicitly scope its use versus validate_email. However, it never names the alternative tool or states explicit when-not conditions, so routing guidance relies on inference.

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