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

Annotations already establish read-only, idempotent, non-destructive behavior. The description adds non-obvious domain behavior: partially billed or reserved items can still have remaining_minor available for new invoices, and state=unbilled is not a sufficient filter by itself.

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 and front-loads the core purpose before the important state caveat. It is short, dense, and wastes no space on repetition.

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 key billing caveat is present, which is important, but with no output schema and only 20% parameter schema coverage, the description should do more to explain the remaining parameters and what the returned billable items contain.

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 only 20%, with only business_id documented in the schema. The description adds meaning for the state filter, but it does not explain limit, offset, or client_id, so it does not compensate for the low schema coverage.

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 clear verb and resource: 'Find billable items.' It is understandable without opening the schema, but it does not explicitly distinguish this from siblings such as billable_record or invoices_list.

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 gives a useful usage caveat for invoicing: remaining_minor is available for new invoices, including partially billed or reserved items, and warns not to rely on state=unbilled alone. However, it does not explicitly say when to use this tool versus alternatives like billable_record or invoices_list.

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