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

Annotations only declare destructiveHint=true; the description adds the materially important behavior that a real email is dispatched to invited contacts, that the invoice is marked sent as a side effect, and that the action is irreversible. It also discloses the underlying API call (POST /api/v1/invoices/bulk with action=email), which is unusually rich disclosure for a mutation tool.

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 short sentences, front-loaded with the risk label 'OUTWARD-FACING' and the irreversibility warning. No filler, and the API mapping is compressed into a single clause.

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?

With only two fully-documented parameters, a destructiveHint annotation, and no output schema, the description covers everything an agent needs: what it does, the side effect, the irreversibility, and the confirmation requirement. Nothing material is missing.

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 documents both invoice_id (hashed id format) and the email_type enum. The description adds no parameter-level detail beyond that, so the baseline 3 applies.

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 ('sends a real email with the invoice to the client's invited contacts, and marks the invoice sent'), which cleanly separates it from the sibling mark_invoice_sent, whose scope is only the status change. An agent can select correctly without opening either 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?

'OUTWARD-FACING' plus 'Cannot be unsent — confirm with the user first' gives clear when-to-use context and a hard guardrail. It stops short of explicitly naming mark_invoice_sent as the lighter alternative when no email is wanted, so it is strong but not fully routing.

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