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

The description adds substantial behavior beyond annotations: the confirm gate ('Requires confirm: true; without it returns the invoice for a final check'), the side effect of releasing time entries so they can be invoiced again, and the paid-invoice restriction. These are not already in the annotations or schema.

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?

Three sentences, front-loaded with the use condition, and every sentence adds a distinct actionable constraint: when to use it, the confirmation requirement, the side effect, and the paid-invoice limitation. No filler 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 covers the most important invocation details: confirmation, invoice eligibility, and post-void side effects. It does not describe the success return value or error details, and with no output schema that is a minor gap, but an agent has enough to call the tool correctly.

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 for all parameters. It adds meaningful semantics for confirm ('Requires confirm: true; without it returns the invoice for a final check') but does not explain invoice_id or the reason parameter at all. The optional reason string remains just a maxLength-limited string with no semantic value.

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 clearly names the verb/resource pair ('void an invoice') and includes the direct use condition 'only when the user explicitly asks to void or cancel an invoice.' It distinguishes this tool from invoice creation, preview, payment, and sending siblings without ambiguity.

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?

Gives an explicit trigger condition ('only when the user explicitly asks to void or cancel an invoice') and a when-not boundary ('Paid invoices cannot be voided'). It does not name sibling alternatives explicitly, but the purpose is narrow enough that an agent can select it correctly.

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