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

Annotations only declare readOnly=false, destructive=false, openWorld=true; the description adds real behavior beyond that: outbound email to a third party ('Reaches other people'), per-call confirmation default that can be toggled, one-at-a-time pacing, and the negative-amount post-refund behavior. It does not describe failure modes (undeliverable email, invalid transaction), which keeps it short of a 5.

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?

Purpose and caution are front-loaded, but the first two sentences restate each other ('Email the invoice...' / 'Sends the invoice of one transaction to the customer, as the Send invoice to customer action does'), and the Cotlet API key sentence reads as boilerplate. Net length is modest but not every sentence earns its place.

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?

For a single-parameter, no-output-schema tool the description covers side effects, pacing, confirmation policy, and auth requirements, which is enough to call it safely. It could still say what a successful call returns or how errors surface, but no output schema exists so the burden is light.

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?

Only one parameter and schema description coverage is 100% ('Transaction ID from list_transactions'), so the schema already carries the semantics. The description adds no format or sourcing detail beyond what's in the schema, matching the baseline 3 for high-coverage schemas.

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 and resource ('Email the invoice of a transaction to its customer') and clarifies scope ('one transaction', 'one at a time'). It is not tautological, though it never explicitly contrasts with siblings such as systeme-io_get_transaction or list_transactions, so differentiation is via scope rather than naming.

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 conditional context ('after a refund it sends the invoice with the negative amount', 'By default you confirm each call') but never states when to choose this over related tools like get_transaction or export_transactions. Usage is implied rather than framed as when/when-not guidance.

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