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

Far exceeds what annotations provide: it discloses that payments stay linked, that it does NOT delete the invoice, that it does NOT reverse payments or convert a paid invoice to credit, and that a cancelled invoice cannot be re-sent. It also states the tool reaches other people and defaults to per-call confirmation, all consistent with openWorldHint and destructiveHint.

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?

Front-loaded with the core effect and efficient overall, but slightly redundant — the balance-zeroing/client-balance-drop is stated twice ('its balance goes to zero and the client balance drops' then 'The invoice balance is zeroed, the client balance drops by that amount'). Otherwise every sentence carries information.

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?

No output schema, yet the description fully covers side effects, status transitions, reversibility boundaries, confirmation behavior, and auth requirements. Nothing an agent needs to call this 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 description coverage is 100% and both parameters are documented in the schema (company default behavior, invoice_number with example and source). The description adds no parameter-level meaning beyond the schema, so the baseline of 3 is appropriate.

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?

States a specific verb+resource ('Cancel a sent invoice') and immediately defines the effect: balance goes to zero, client balance drops, status becomes Cancelled. An agent can distinguish it from siblings like send_invoice, record_payment, and get_invoice without opening a schema.

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?

Explicitly enumerates the eligible states (Sent, Partial or Paid), names the contrasting 'Reverse' operation and explains why this tool is not it, and states the precondition ('the user's Cotlet API key with access to this app'). It also instructs to confirm with the user before each call.

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