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

Annotations already declare non-read-only, destructive, non-idempotent, and open-world behavior, so the bar is lower. The description still adds concrete value: what is transmitted (the invoice plus its PDF), who receives it (the address stored on the invoice), and who it appears to come from (the person's business name), plus the explicit warning that a real email goes out.

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?

Two short sentences with no filler, and the core action is front-loaded ahead of the sender/recipient detail. Every clause carries 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?

For a one-parameter, no-output-schema action whose annotations already communicate the safety profile, the description covers what is sent, to whom, and from whom. It omits failure conditions (e.g., invoice lacking a client email address) and whether the send can be undone, which would be minor additions.

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 0% and the sole parameter, invoiceId, is never explained in the description. The text implies an invoice (and its stored client address) is the subject of the call, but adds no format or identification detail beyond that implication; a single obvious parameter keeps this at an acceptable middle level.

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 ('Email an invoice') and adds scope detail: the PDF, the client address on the invoice, and the sender identity. An agent can separate this from create_invoice, list_invoices, and mark_invoice_paid without opening any schema.

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?

There is no explicit when-to-use framing or named alternative among the sibling tools. The sentence 'This sends a real email to the client' functions as an implicit caution that the tool should only be invoked when an actual client-facing send is intended, but the agent is left to infer when this is appropriate versus other invoice tools.

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