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

Annotations already declare non-read-only, destructive, non-idempotent, open-world behavior, so the baseline bar is lower — but the description adds nothing beyond them. It does not say what gets overwritten (whole draft vs. only supplied fields), whether omitted fields are cleared, or what permissions/account context are required for a destructive mutation.

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?

It is a single short sentence with no filler, so it is concise and front-loaded. However, brevity here is emptiness rather than efficiency — the sentence carries no actionable content for an agent.

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 12-parameter destructive mutation with no output schema and no parameter documentation, the description is far too thin. An agent cannot determine which fields are patchable, what happens to unmentioned fields, or how attachments and reply metadata are handled.

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?

The schema has 12 parameters at 0% description coverage, including non-obvious ones like replyAll, replyToMessageId, and the attachments sub-object, and the description never mentions a single field or the update/patch semantics. With no output schema and no enum guidance either, the description does nothing to compensate for the coverage gap.

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 restates the name and title almost verbatim ("update_draft" / "Update draft" → "Update an existing mailbox draft") without adding scope or distinguishing it from create_draft, delete_draft, or get_draft. It names a verb and resource, but a reader learns nothing not already in the identifier.

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?

There is no statement of when to use this tool versus its siblings, no mention of prerequisites (does the draft have to exist? must it be unsent?), and no indication of how it differs from send_email or create_draft. The only implied usage is the tautological 'existing draft'.

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