Forward a message

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

Annotations already mark destructive and non-idempotent, and the description adds meaningful behavioral detail: immediate sending, no undo, attachments included, comment placement, and the separate Mail.Send permission requirement. No contradiction with annotations.

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 tight sentences front-load the core behavior and warning, then add only necessary context about comment placement and permissions. Every clause contributes actionable information with no filler.

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 3-parameter tool with no output schema, the description covers what the action does, side effects, safety guidance, and required permission. An agent has enough to decide whether to call it and what to tell the user before invoking.

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 the schema already documents id, to, and comment. The description adds only that attachments are included and that no undo exists, which is behavioral context rather than new parameter semantics; the comment placement detail essentially repeats the schema description.

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, and mode ('Forwards an existing message immediately, attachments included') and explicitly distinguishes itself from draft creation. An agent can reliably tell this apart from mail_send, mail_create_draft, and mail_reply.

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?

Gives clear context: the tool acts immediately, includes attachments, and is not a draft; it also tells the agent to confirm recipients with the user first because there is no undo. It does not explicitly name alternative tools or state 'use X instead', but the actionable guidance is strong.

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