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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds no additional behavioral context such as error handling, rate limits, or authentication requirements. Since the description carries minimal burden given annotations, it adds no extra value beyond the obvious.

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, concise sentence that conveys the essential action and distinguishing factor. No fluff or redundancy, and the key qualifier 'by Id' is front-loaded. Perfectly efficient.

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 tool is simple with only 2 parameters, no output schema, and no nested objects. The description covers the action and scope but does not mention the return value structure or behavior when the invoice is not found. While annotations cover safety, a brief note on the response or error case would make it more complete.

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 both 'id' and 'company' are already documented. The description does not add further meaning about parameter formats or relationships. With full schema coverage, baseline 3 is correct; the description adds no extra nuance.

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 the verb 'Get', the resource 'a single invoice', and the key qualifier 'by Id'. This distinguishes it from sibling search tools like search_invoices and list tools like get_open_invoices, making the purpose unmistakable.

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 when an invoice ID is available, and the schema requires 'id'. However, it does not explicitly name alternatives or state when not to use this tool (e.g., when searching without an ID). Guidance is implied rather than explicit, so a 3 is appropriate.

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