mail_update_draft

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

Adds rich behavior beyond the annotations: the save-new-before-remove ordering, attachment preservation default, that supplied attachments are appended, that text/html replaces the old alternate body, and that the return is the NEW draft UID. The 'Never sends mail' guard is a valuable safety clarification for a mutation tool with destructiveHint=false.

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?

Front-loaded with verb and mechanism, then each subsequent clause carries unique information (requirements, attachment semantics, body replacement, return value, safety). No filler sentences.

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 mutation tool with no output schema, the description covers the critical return value, preservation semantics, body-replacement behavior, and safety boundary. An agent has what it needs to call it correctly.

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 0% across 12 parameters, so the description must compensate, and it only covers about half (uid, uidValidity, preserveAttachments, text, html, attachments). accountId, folder, to, cc, bcc and subject are left entirely to their names.

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 and resource ('Update an existing server draft') plus the underlying mechanism ('saving a new version before removing the old one'). This implicitly separates it from draft-creation siblings like mail_prepare_draft and mail_save_draft, though it does not name any alternative explicitly.

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 for when the tool applies (an existing draft that must carry exact UID, observed UIDVALIDITY and UIDPLUS) and a boundary ('Never sends mail'). It stops short of naming the sibling to use instead for a new draft, so it lacks an explicit alternative path.

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