Add a line item or charge to an existing invoice by specifying the invoice ID, item description, unit price, and quantity.
Add a line item or charge to an existing invoice.
| Name | Required | Description | Default |
|---|---|---|---|
| price | Yes | Unit price | |
| quantity | Yes | Quantity (default 1) | |
| invoice_id | Yes | Parent invoice ID | |
| description | Yes | Item description | |
| reference_id | No | Polymorphic model ID | |
| reference_type | No | Polymorphic model type (e.g. App\Models\Service) |
Changes observed during successful MCP inspections.
v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden of behavioral disclosure. It indicates this is a mutation operation on an existing invoice, but it omits permissions required, reversibility, side effects on invoice totals, and what the operation 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?
A single, front-loaded sentence that states the action and its scope with no wasted words. It is appropriately sized for the core operation.
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 annotations and no output schema, the description is too thin. It does not explain return values, side effects, permissions, or how the new item affects the invoice, leaving important context 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 description coverage is 100%, so the schema already documents all parameters. The description adds no parameter-level meaning beyond the generic mention of 'line item or charge', leaving this at the baseline for fully covered schemas.
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 uses a specific verb ('Add') and resource ('line item or charge'), and scopes it to an existing invoice, which distinguishes it from sibling invoice operations like create_invoice or update_invoice. It does not name an alternative sibling explicitly, but the purpose is clear.
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 description implies usage by stating it adds to an existing invoice, but it gives no explicit when-to-use guidance, no conditions for choosing this tool over alternatives like create_invoice, and no prerequisites or exclusions.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.