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

Annotations already indicate this is a non-read-only, non-idempotent operation. The description adds that it returns the new invoiceId and that line items are optional, which is useful. It does not detail side effects or error conditions, but for a create operation the behavior is largely captured.

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 two sentences, immediately states the primary action, and includes the return value. No fluff or redundancy.

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?

The description, combined with the complete schema and annotations, covers the essential aspects for a create invoice tool. It mentions the key return value and optional line items. It lacks some nuance (e.g., server-side total calculation is only in schema), but overall it is adequate.

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 parameters are already well documented. The description adds minimal param semantics ('Optionally include line items inline'), which reinforces the schema. It does not go beyond the schema in explaining formats or defaults.

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 states 'Create a new invoice for a customer' with a specific verb and resource. It distinguishes from sibling invoice tools (e.g., get_invoice, void_invoice) by explicitly naming the creation action and mentioning returning the invoiceId.

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 provides clear context on what the tool does and notes that line items are optional ('Optionally include line items inline'). However, it does not explicitly exclude alternative tools, but there are no other tools that create invoices, so the usage is unambiguous.

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