Mark an invoice paid

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

No annotations are provided, so the description carries the full behavioral burden, and it delivers: it discloses the major-units convention, the additive (never replace) semantics, the omit-to-settle behavior, and the overpayment-refusal error including that the open balance is named. This is rich behavioral disclosure for a mutating tool with zero annotation coverage, though it stops short of describing what a successful call returns.

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?

Three tight sentences with zero filler. The core action is front-loaded, and the most decision-relevant clarifications (units, add semantics, refusal behavior) are packed into the two supporting sentences. Every clause earns its place.

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 5-parameter mutating tool with no output schema, the description covers the payment semantic well (which is the riskiest part of the call) but does not mention the return shape of a successful payment or what information the agent gets back (e.g., remaining balance). The call semantics are adequately complete; the response semantics are left open.

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 high at 80%, and the schema already documents the additive/omit-to-settle behavior of 'amount'. The description re-asserts the additive semantics and adds the major-units convention and the overpayment-refusal nuance, which is genuine added value, but most parameter meaning is already carried by the schema, so it lands at 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?

The description states a specific action — 'Record a payment on one invoice' — with a clear verb, resource, and scope. It is unambiguous against siblings like invoice_create, invoice_get, invoice_list, and invoice_pdf, which all perform clearly different operations.

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?

No alternatives are named and no explicit when-to-use vs when-not-to-use guidance is given. The 'one invoice' scoping implies single-invoice behavior, but nothing tells the agent when to reach for this tool over related siblings or how it relates to invoice_create (which could also affect invoice state).

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