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

With no annotations, the description carries the burden and it does disclose the critical non-obvious behavior that `prices` is wholesale-replaced while omission preserves it. It also implies partial update semantics for other fields. It does not cover permissions, error cases, or response, but the main side-effect warning is present.

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 entire description is a single focused sentence, front-loading the operation and then adding the essential replacement caveat. No filler or repeated schema information.

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 7-parameter tool with no annotations, no output schema, and 0% schema coverage, the description is under-specified. It addresses only the `prices` footgun and leaves the meaning of `unitPrice` vs `prices`, the required `id`, and tax/label/description fields to inference. An agent would likely need additional documentation to safely use all fields.

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 0%, and the description only explains `prices`; the other six parameters (`id`, `name`, `unitLabel`, `unitPrice`, `description`, `defaultTaxRate`) receive no semantic clarification. This is a significant gap because the schema provides no property descriptions. It earns credit for the one important parameter but fails to compensate for the rest.

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 opens with 'Update an item,' a clear verb+resource statement, and the tool name plus sibling set (invoice_items_create/list) make the target resource evident. It further clarifies the update semantics around pricing, which is specific to this tool. It doesn't explicitly say 'invoice item' but this is unambiguous from context.

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?

It provides explicit conditional guidance for the `prices` parameter: omit to preserve, send to replace, and gives a concrete renaming scenario. It does not contrast with create/list or state when update is inappropriate, so tool-selection guidance is implicit rather than fully explicit.

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