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

Annotations only say it is a non-read-only, open-world, non-destructive call; the description adds the important behavioral facts beyond that — the email actually reaches an external customer, confirmation is on by default and can be disabled, a user confirmation is advised per call, and an API key with app access is required. That is exactly the kind of side-effect context an agent needs before invoking.

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?

The core behavior is front-loaded, but there is redundancy: the confirmation instruction appears twice ('By default you confirm each call; you can switch that off' and 'Reaches other people: confirm with the user before each call'), and 'The customer receives the email' restates the opening sentence.

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 behavior, scope limits, error case, confirmation policy, and auth needs. It is essentially complete, with only a slightly confusing 'Cotlet API key' phrasing that could mislead about the credential source.

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?

There is a single parameter with 100% schema coverage, and the schema already documents that invoice_id comes from list_sales_invoices or create_sales_invoice. The description mentions the invoice concept but adds no parameter-level detail, so this is the baseline 3.

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+effect: emails the customer that an invoice is open and re-attaches the invoice, and equates it to the Herinnering button on an open invoice. An agent can distinguish this from send_invoice (which sends the invoice originally) without opening the 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?

Gives clear when-it-works / when-it-fails conditions: regular invoices only, not e-invoices, and it errors on already-paid invoices. It does not name alternative sibling tools (e.g. send_invoice or a payment-registration path) for the cases it excludes, 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.