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

With no annotations, the description discloses the essential auth requirement and the read-like nature of 'Get,' plus that line items are included. It does not describe possible errors, response shape, or side effects, but for a simple fetch tool these omissions are moderate rather than severe.

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 short sentences front-load the core purpose and add the auth note. The 'Required: invoiceId (string)' fragment is redundant with the schema, but the overall size is appropriate.

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 is adequate for a simple retrieval tool: it identifies the target, the auth requirement, and that line items are returned. It lacks guidance on where invoiceId comes from (likely listInvoices) and what errors/return shape to expect, and there is no output schema or annotations to cover those gaps.

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?

The description merely restates that invoiceId is required and a string, which duplicates the input schema and adds no meaning about how to obtain or use it. The sessionKey parameter is well documented in the schema, but the description does not compensate for invoiceId's missing schema description.

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?

Description states a specific verb and resource: 'Get detailed information about a specific invoice including line items.' This clearly distinguishes it from list-oriented siblings like listInvoices and getInvoiceStatistics by emphasizing a single invoice and its line items.

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 intended use is implicit: call this for one invoice's details rather than listing invoices. However, it never explicitly names alternatives, when-not-to-use conditions, or the prerequisite of obtaining invoiceId from listInvoices; 'Requires authentication' is a prerequisite, not usage-routing guidance.

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