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

Annotations only say destructiveHint=true; the description adds far more: the invoice is retained but permanently unpayable and uneditable, and the call runs a propose→confirm cycle returning status='confirmation_required' with an action_id and plan_token, with the write occurring only after confirm_action. That is exactly the kind of two-phase, irreversible behavior an agent must know before invoking.

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 compact sentences with the effect front-loaded, followed by a clearly labeled CONFIRMATION block that flags the non-obvious propose/confirm protocol. No redundant restatement of the title or annotations.

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?

There is no output schema, and the description compensates by describing the exact return shape ('confirmation_required', action_id, plan_token) and the follow-up tool. For a single-parameter destructive mutation, nothing an agent needs to call it correctly is missing.

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 coverage is 100% and the single `invoice` parameter already documents accepting a number as spoken (INV-12, 12) or an id. The description adds no further parameter guidance, so the schema does the work; baseline 3 applies.

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?

Names a specific verb and resource ("Cancel (void) an invoice") and immediately defines the resulting state: stays numbered in the books, status Cancelled, no longer payable or changeable. This distinguishes it cleanly from siblings like invoice_mark_paid, invoice_undo_payment, or invoice_update without needing to enumerate them.

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 makes clear the context in which to use it: when an invoice should be voided but remain in the books rather than be paid or edited. It does not explicitly name alternatives or exclusion cases (e.g. "use invoice_mark_paid instead if the invoice was actually settled"), so it stops short of a full when/when-not routing statement.

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