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

Beyond the annotations (readOnlyHint=false, destructiveHint=true), the description reveals critical behaviors: sending is asynchronous, delivery requires user approval in Caribooks, the memo cannot be unsent, and the record must still exist at delivery time. This is exactly the kind of behavioral context an agent needs and goes well beyond the structured annotation hints.

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, each earning its place: the first states the primary action, the second explains asynchronous delivery and record-liveness constraints, and the third discloses irreversibility and the required user approval step. Critical warnings are front-loaded and the language is efficient.

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 send action with no output schema, the description covers everything an agent needs to know: what happens, when it happens, what can prevent it, and what the user must do. Combined with a fully described schema, this is a complete operational picture.

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?

The input schema has 100% description coverage for all four parameters, so the schema already carries the semantic weight. The description does not add parameter-level detail, but it does reinforce the need for explicit approval, which complements the 'confirm' parameter's 'must be true' requirement.

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?

The description states a specific verb ('Email'), a specific resource ('a credit memo ... as a PDF from QuickBooks Online'), and a clear outcome ('mark it sent'). This clearly distinguishes it from sibling send_* tools that target other document types like invoices, estimates, or sales receipts.

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 that this tool is for emailing credit memos and that it is subject to an approval workflow, which is essential context for deciding when to invoke it. It does not explicitly name sibling alternatives or state conditions to avoid using it, but the resource-specific purpose is sufficiently clear.

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