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

Annotations already declare the safety profile (not read-only, idempotent, non-destructive, closed world), and the description adds real behavior beyond them: patch semantics ('nur übergebene Felder werden geändert'), the null-clears-a-field rule, and the important side-effect caveat that existing documents keep the address they were created with. Missing are error behavior and what the call returns, which keeps it below 5.

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?

Three short sentences, front-loaded with purpose, then the two rules an agent most needs. Every sentence carries information and nothing is padded.

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 15-parameter mutation with 27% schema coverage and no output schema, the description is too thin: it does not explain the return value, failure modes, or the meaning of the majority of fields. The null-clearing and historical-address notes are the right kind of content but cover only a fraction of what an agent needs.

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 only 27% across 15 parameters, so the description carries most of the burden and does not meet it. It adds the valuable null-versus-omitted rule that applies to every field, but says nothing about the undocumented parameters (city, phone, street, vat_id, postal_code, address_form, is_business, contact_* fields), including the non-obvious sie/du enum.

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 ('Einen Kunden in der Kartei ändern'), which is unambiguous and clearly distinct from create_customer, get_customer or update_document. It does not explicitly name or contrast with any sibling, so it stops short of a 5.

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 never says when to reach for this tool versus create_customer (for new records) or get_customer (for reads), nor does it state prerequisites such as required permissions or whether the customer must already exist. Usage is only inferable from the verb 'ändern'.

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