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

Beyond the annotations, the description adds the critical behavioral facts that the email is sent immediately and cannot be recalled, and clarifies that delivery can be a link or an attached file. It does not contradict the annotations: openWorldHint matches the external email side effect, and destructiveHint=false remains reasonable because no data is deleted.

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?

The description is three short, front-loaded sentences with no filler. The 'WRITE' prefix, behavioral warning, and endpoint each earn their 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 7-parameter tool with full schema coverage and no output schema, the description covers the core action, delivery modes, and irreversible side effect. It does not describe success/failure behavior, but that is a minor gap given the complete input schema.

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%, so every parameter is already documented, including defaults for subject, delivery, and language. The description reinforces the link-vs-file delivery choice but adds no syntax, constraints, or default details beyond the schema.

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 uses a specific verb (email) and resource (a document, specifically an invoice via the endpoint), and states the two delivery modes. An agent can immediately tell this is a send-invoice-by-email action, and no sibling tool overlaps with that purpose.

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?

It makes the operation's context clear with the explicit 'WRITE' marker and the endpoint, and the irreversibility warning signals that it should be used deliberately. It does not name alternatives or state when not to use it, but among the sibling tools there is no competing email-sending operation.

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