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

Annotations only say this is a non-read-only, open-world, non-destructive mutation. The description goes well beyond that: it discloses the side effect that the linked bank transaction becomes booked, the state precondition (only unpaid receipts), the default per-call confirmation and that it can be disabled, and the required API-key access scope.

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?

Purpose is front-loaded, but the definition repeats itself: the opening sentence and 'Marks a receipt as paid like Als bezahlt markieren' say the same thing, and the confirmation requirement is split across two sentences ('By default you confirm each call...' and 'Reaches other people: 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 mutation tool with no output schema and thin annotations, the description covers modes, preconditions, auth, and confirmation behavior, which is close to what an agent needs. It doesn't state what happens if the receipt is already paid or how errors surface, which is the remaining gap.

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 100%, so the baseline is 3, but the description adds the conditional relationship between parameters that the schema does not: transaction_id changes the booking behavior, and paid_on is only the payment date when no transaction is supplied.

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 (mark a receipt/voucher as paid) and immediately scopes the two ways it can be done. The receipt/Beleg framing distinguishes it from the sibling sevdesk_mark_invoice_paid without needing to open either schema.

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 explains when to pass transaction_id (link to a bank transaction that becomes booked) versus when to omit it (book on the account with paid_on, suiting a Verrechnungskonto), plus the precondition that only unpaid receipts qualify. It does not name the sibling mark_invoice_paid as an alternative, so it stops short of full routing guidance.

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