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

Annotations already signal destructiveness, but the description adds substantial behavioral detail: unconfirmed requests return a preview/token/URL, human approval is required, sender and subject are derived, dry_run only produces an estimate, and operation_unknown_state is handled. This meaningfully complements the annotations without contradicting them.

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 every sentence earns its place: purpose, approval workflow, permission, constraints, async status handling, and dry-run behavior are all covered without filler. It is front-loaded with the primary action before diving into details.

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?

Despite no output schema, the description covers the full invocation context: prerequisites, confirmation flow, limitations, failure conditions, async state resolution, and dry-run semantics. An agent has enough information to decide when to call it and how to handle the approval and retry lifecycle.

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?

With only 20% schema description coverage, the description compensates well by explaining dry_run, idempotency_key, and confirmation_token semantics, and by tying reply_id to the existing thread. Body_text is less explicitly described but is inferable from 'Send a real email' and the parameter name.

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 clearly states the action, resource, and context: sending a real email in an existing inbound reply thread from the receiving mailbox. This strongly differentiates it from read-only siblings like get_reply and get_replies, and from other sending tools by focusing on the reply thread case.

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 explicitly explains when to use it, the required approval flow, the non-default reply:send permission, the one-reply-per-inbound-message limit, and the refusal of suppressed contacts. It also routes unresolved async states to get_operation, giving clear practical guidance.

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