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

Annotations already mark the tool as read-only, idempotent, and open-world. The description adds useful behavior: it validates both format and Modulo 11 check digit, and it performs a registry lookup rather than only local validation. This is consistent with the annotations and provides extra context about what happens during the call.

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 with no filler. The core function is front-loaded and the usage guidance follows in a compact, actionable clause. Every sentence adds 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 one-parameter, read-only lookup tool, the description covers what it validates, that it checks the registry, and when to use it. The lack of an output schema means return details are not specified, but the simple scope and strong annotations make the description sufficient for correct selection and invocation.

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 has 100% description coverage for the single required parameter ('Zu prüfende UID'), so the baseline is 3. The description adds that the UID is Swiss and subject to check-digit validation, but it does not specify accepted formats such as CHE prefix or separators, so it does not go beyond the schema baseline.

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 states a precise verb and object: 'Prüft eine Schweizer UID auf Format und Prüfziffer' and additionally says it looks the UID up in the registry ('schlägt sie im Bestand nach'). This is specific enough to distinguish uid_pruefen from siblings like firma_suchen or firma_details, which are about finding or retrieving company data.

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?

It gives an explicit trigger: 'Nutze dies, bevor du eine UID in ein System übernimmst — Tippfehler werden so erkannt.' This tells the agent when the tool should be used. It does not name alternatives or give explicit when-not-to-use conditions, so it falls just short of a 5.

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