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

Goes well beyond the annotations (readOnlyHint=false, destructiveHint=false, openWorldHint=true): it discloses that setting paid also sets the payment date, that cash VAT invoices get VAT settled that day, that confirmation is on by default but can be switched off, and that calls reach other people. This is unusually rich side-effect and auth disclosure for a mutation tool.

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 purpose, then alternatives, then confirmation/auth notes. Mostly earns its place, though 'Changes the status of one invoice' slightly repeats the opening clause.

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?

With no output schema, the description still supplies purpose, side effects, sibling alternative, confirmation behavior, and auth requirements. 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 description coverage is 100%: status values (issued, sent, paid, partial, rejected; default paid) and invoice_id sourcing from list_invoices are already documented. The description adds only the consequence of the 'paid' value, so the baseline 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 ('Set an invoice status... Changes the status of one invoice') and the scope ('without recording a transfer'). It is clearly distinguishable from the sibling record_payment, which it names explicitly.

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 routes the agent: 'Use record_payment when there is a transfer to record.' It also states preconditions (confirm each call by default, needing a Cotlet API key with app access), covering when-to-use and how to invoke.

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