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 useful behavioral context: it is paginated, returns newest first, and supports status filtering for common questions. It does not describe pagination mechanics in detail, but the output schema likely covers that. The description adds value beyond annotations without contradicting them.

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 sentences with no waste. The core purpose and ordering are front-loaded, followed by the read-only and pagination traits, then a practical usage hint. Every sentence earns its place.

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 has an output schema, so return values are covered. The description covers the key behavioral traits: read-only, paginated, newest first, status filtering. It does not mention the date range filter or the filter object structure, but the schema provides those details. For a list tool with annotations and an output schema, this is nearly 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 0%, so the description must compensate. The description mentions filtering by status and pagination, which maps to the 'statuses' and 'pageToken'/'pageSize' parameters. However, it does not explain the filter object structure, the date range fields, or the UUID wrappers. The description adds some meaning but leaves the agent to infer the rest from the schema.

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 states a specific verb ('Lists'), a resource ('a company's invoices'), and the ordering ('newest first'). It also names the key fields returned (client, amount, due date, status), which distinguishes it from generic list tools. The sibling list includes invoice_get_invoice and invoice_get_invoice_pdf_url, so this description clearly identifies the list operation.

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 gives clear context: it is read-only, paginated, and can be filtered by status to answer 'what is unpaid' or 'what is overdue'. It does not explicitly name alternatives or exclusions, but the context is sufficient for an agent to know when to use it. A 4 is appropriate because it provides clear usage context without explicit when-not-to-use guidance.

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