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

The description adds substantial context beyond the annotations: the email goes to a third party, cannot be recalled, every call sends another email, and rate limits of 50 per day, 5 per invoice, and 5 per recipient apply. It also discloses side effects such as recording the send in email history and saving the address as the invoice recipient if none exists.

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 dense but well structured: purpose first, then delivery semantics, preconditions, limits, and side effects. Every sentence contributes operational 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?

Given the mutation and external-send nature of the tool, the description covers preconditions, irreversible side effects, rate limits, history recording, and recipient persistence. It leaves no critical gap for an agent deciding whether and how to call it.

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 coverage is 100%, so the schema already defines all four parameters. The description still adds useful meaning by clarifying that "to" is where the email is sent and that the address may be persisted as the invoice's recipient, which goes beyond the raw 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 states a specific verb and resource: emails a finalized invoice as a PDF attachment to the address in "to." This clearly distinguishes it from siblings such as get_invoice_pdf, send_reminder, and create_invoice.

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 explicitly says to use it to deliver an invoice to a customer, and clarifies that the invoice must already be finalized and that the tool does not finalize drafts or spend credits. These are clear when-to-use and when-not-to-use constraints.

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