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

Goes well beyond the annotations: it describes the side effects (creates a cancellation invoice, marks it paid, sets the original to cancelled, consumes the next invoice number) and the human-in-the-loop confirmation requirement. Annotations say destructiveHint=false, and the description is consistent with that since no data is deleted — the invoice is transitioned, not erased.

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 core behavior and mechanism before qualifications, and most sentences earn their place. It loses a point for mild redundancy: the confirmation requirement is stated twice in slightly different words ("By default you confirm each call" and "confirm with the user before each call").

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 mutation tool with no output schema, the description covers trigger conditions, side effects, number-range behavior, the paid-invoice exclusion, and the confirmation/auth requirements. Nothing an agent needs in order to call it correctly is missing.

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?

With a single parameter at 100% schema coverage, the schema already documents invoice_id and its source (list_invoices). The description adds no parameter-specific detail beyond implying the original invoice is referenced, so the baseline 3 applies.

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 (cancel an invoice) plus the exact mechanism (creates a Stornorechnung/cancellation invoice that references the original). This clearly separates it from siblings like sevdesk_mark_invoice_paid, sevdesk_send_invoice, and sevdesk_create_invoice_draft.

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?

Explicitly states the applicable case (invoice is open or due) and the exclusion (a paid invoice cannot be cancelled this way and needs a credit note). It also directs the agent to confirm with the user before each call, which is actionable routing guidance.

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