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

Annotations only supply destructiveHint=true, so the description carries the real disclosure burden and does well: it reveals the status transition (out of draft) and the financial side effect (amount added to client balance), plus the underlying API route. It omits reversibility and whether the balance effect can be undone, which matters for a destructive mutation.

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?

Two tight sentences: the core action and its key caveat are front-loaded, followed by the side effects, with the API route last. No filler or redundancy.

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 with no output schema and only a destructiveHint annotation, the description supplies the essential state change and balance impact an agent needs. It could go further on reversibility or the expected response, but nothing critical 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?

Schema coverage is 100% and the single invoice_id is fully documented with format guidance (hashed id example), so the schema does the heavy lifting. The description adds no parameter-level meaning beyond that, making the baseline 3 correct.

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 draft invoice as sent') and immediately narrows scope with 'WITHOUT emailing it', which cleanly separates it from the sibling invoiceninja_email_invoice. An agent can pick between the two without opening 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?

The 'WITHOUT emailing it' clause gives clear context for when this tool applies versus the email path, and 'moves it out of draft' implies the required precondition state. It never names the alternative tool explicitly or states what happens if the invoice is already sent, so it stops short of full 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.