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

Without annotations, the description provides essential behavioral traits: amounts must be in 'integer cents', the server automatically calculates totals, and it does not trigger an email notification. These are critical operational details.

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 description is perfectly sized. The first sentence establishes the core action, and the second sentence immediately addresses critical implementation constraints, ensuring no waste of words.

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?

Given the complexity of billing and invoicing, the description addresses all necessary constraints: unit handling (cents), calculation logic (server-derived totals), and side effects (no email). It is contextually complete for the operation.

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?

While the schema confirms the data types, the description adds high-value semantics by explaining the conversion rule (25000 means $250.00) and clarifies that the `total` is not an input parameter as it is derived by the server.

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 clearly and immediately defines the tool's purpose: creating a DRAFT invoice for an existing client. This scope distinguishes it from other invoice-related siblings like list_invoices or share_invoice.

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 clearly states the required context ('for an existing client'), which is a usage guideline. However, it does not explicitly guide the agent on when to use this tool versus potentially an 'invoice generation' tool (if one existed), focusing instead on the state (Draft).

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