Create Line Item

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

With no annotations present, the description carries the full behavioral burden. It does disclose one genuinely useful behavioral constraint — the target invoice must be a draft — but omits permissions/auth requirements, whether the operation recalculates invoice totals, and any rate-limit or failure behavior.

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 tightly written sentences with zero filler; the core action and the draft-invoice constraint are front-loaded before the explanatory detail.

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 9 parameters, no annotations, and no output schema, the description covers the essentials of what the tool does and the draft precondition. It leaves gaps on optional-parameter usage (discount, position, service_type_id) and provides no context on outcomes, which the absence of an output schema makes slightly more noticeable.

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; the schema already documents all nine parameters including unit_id enum values and required flags. The description restates that description/quantity/unit_price define the billable row and that tax_rate_id sets per-line tax, which is mildly reinforcing but adds no syntax or format detail beyond the schema.

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 (create a line item) and adds the scope constraint 'on a draft invoice,' which meaningfully narrows what the tool does. It does not explicitly name siblings like update_line_item or list_line_items, so differentiation is implicit rather than stated.

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 phrase 'on a draft invoice' implies a precondition and context of use, which is more than nothing. However, it never says when to use this versus update_line_item, list_line_items, or delete_line_item, and gives no guidance on error/failure cases like a non-draft invoice.

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