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

Goes well beyond the annotations: discloses that both invoices remain in the overview (clarifying the reversible/non-removing nature), requires inStap for creation and inKaart for journal write-off, notes default per-call confirmation that can be disabled, warns it reaches other people, and states the API-key access requirement. This is rich operational context for a mutation 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?

Purpose and scope are front-loaded, and most sentences earn their place. However, the confirmation behavior is stated twice ('By default you confirm each call' and 'confirm with the user before each call'), and the 'as Crediteren does' reference is a minor distraction.

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, the description covers the required permissions, confirmation/consent behavior, external visibility, and auth - everything an agent needs to call it responsibly. Return values are not addressed, but the absence of an output schema makes that acceptable.

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 'invoice_id', 'lines', and 'action' are already documented. The description reinforces the partial-credit concept of 'lines' but adds no syntax, defaults, or format detail beyond the schema, so baseline 3 is appropriate.

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+resource ('Credits a sales invoice') plus scope (full or partial) and the mechanism ('Copies the invoice into a new one with negative amounts'). This clearly distinguishes it from siblings like create_sales_invoice or get_sales_invoice.

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?

Explains when full vs partial crediting applies ('optionally with fewer lines or quantities', 'Omit to credit the whole invoice') and notes the inStap/inKaart permission split. It gives clear context but never names an alternative sibling to route to, so it falls short of explicit when/when-not guidance.

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