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

Beyond what readOnlyHint=false and destructiveHint=true already convey, the description adds non-obvious behavior: attachments bypass the chat transport, the comment renders above the forwarded text, recipient allowlist is enforced, and the draft path avoids actual sending. None of this contradicts the 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?

Roughly 40 words across three sentences, each earning its place: core behavior with attachment routing, comment placement, and constraints/draft mode. Information is front-loaded with the highest-value fact first.

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?

Adequate for a 10-parameter compose tool: covers attachment handling, comment, draft vs send branching, and the allowlist prerequisite. The main gap is that with no output schema, the description never states what the tool returns or how an agent later references a saved draft.

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 60% and most parameters already carry descriptions. The description adds placement semantics for comment ('above the forwarded text') and clarifies include_attachments behavior via the no-chat-pass-through clause, but it does not compensate for the uncovered portion of the parameter surface (e.g., cc/bcc interaction).

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 (forwards) and resource (a message), and immediately adds distinguishing scope: attachments are included and routed directly 'without the files passing through the chat.' The comment-placement and draft-mode details further separate it from reply and send siblings, so an agent can identify which tool to use without opening the 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?

Gives actionable constraints (recipients must match send_allowlist; as_draft redirects to Drafts) but never names or positions alternatives such as reply_send, reply_draft, or send_message, which are direct siblings in the compose space. When to choose forwarding over replying is left to inference.

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