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

Annotations declare destructive/openWorld/non-idempotent, and the description adds concrete behavior beyond them: one copy filed in Sent, draft leaves Drafts, no signature is appended, Bcc/Reply-To drafts are refused, and the action delivers real mail irreversibly. This is exactly the extra context a mutation tool needs.

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?

Long but front-loaded: the core action and its effect come first, then prerequisites, then refusal cases. Every sentence carries distinct information, though the paragraph-length delivery is dense and could be tightened slightly without losing content.

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 no output schema, the description still covers what an agent needs: preconditions, the uid volatility hazard, refusal branches with routing, and the irreversible side effect. Nothing essential about invoking it correctly 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% and the single uid parameter is documented there, so the baseline is 3. The description adds real value over the schema by warning that the uid is volatile ('a draft gets a new uid each time anyone saves it'), explaining why it must be fetched immediately before sending.

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 precise verb+resource ('send a draft that is already in the Drafts folder') and scopes it against siblings: it is not send_email (new mail) and not approve_and_send (approval path). The 'exactly as it sits there' framing tells the agent no re-composition happens.

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?

Explicit prerequisites and alternatives: read with read_email on Drafts first, take uid from list_emails on that folder now, and approval-gated drafts must go through approve_and_send instead. Also names the two refusal cases and says each refusal states the remedy.

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