validate_hetu

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

With no annotations, the description fully informs the agent: it only validates structure (format and check digit) and does not verify real-world existence. The breakdown of components (DDMMYY, century sign, etc.) clarifies what is checked. This is sufficient for a validator tool.

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?

The description is two sentences, immediately front-loading the imperative 'USE THIS' followed by the purpose. The second sentence provides necessary technical detail. No wasted words; every sentence adds value.

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 simple one-parameter validator with no output schema, the description is complete: it explains the input, the validation logic, and the limitation ('structure only'). No missing information for effective use.

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?

The schema describes the 'hetu' parameter with an example. The description adds structural details (DDMMYY + century sign + individual number + mod-31) which help the agent understand valid input beyond syntax. Schema coverage is 100%, so this extra context earns a 4.

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 clearly states the tool's purpose: 'verify a Finnish henkilötunnus (HETU / personal identity code)'. It specifies the exact components validated (DDMMYY + century sign + individual number + mod-31 check character) and contrasts with guessing. This is a specific verb-resource pair that distinguishes it from sibling 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?

The description explicitly instructs to use this tool 'before relying on it' and warns against guessing the check character. While it doesn't list when not to use, the context of sibling validators implies it's for Finnish HETU only. The guidance is clear and actionable.

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