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

Annotations already declare destructiveHint=true, idempotentHint=true, and readOnlyHint=false, so the safety profile is covered. The description adds value beyond that by disclosing the 'not been sent' applicability constraint and the text-handling behavior ('Plain text is fine; line breaks are kept'), though it says nothing about auth requirements or failure modes.

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 short sentences, all front-loaded with the action and scope first, then the ID source, then formatting notes. No filler or redundancy.

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?

There is no output schema and no nested parameters, so the description carries the remaining burden; it covers what is overwritten, where the ID comes from, and body formatting. It is slightly thin on error behavior (invalid ID, already-sent draft) for a destructive mutation, but adequate overall.

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%, so the baseline is 3, but the description adds real meaning beyond the schema's terse 'The new body.': it clarifies that plain text is acceptable and that line breaks are preserved, which directly affects how the caller should format the body parameter.

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 ('Replace the subject and body of one draft') and constrains scope to a draft 'that has not been sent', which cleanly separates it from sent-mail tools and from draft creation tools like draft_reply. An agent can distinguish it from discard_draft, get_draft_reply, and draft_reply without opening any 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 the key prerequisite and routing hint: 'Get the draftId from list_pending_drafts,' and restricts applicability to unsent drafts. It does not explicitly contrast with discard_draft or state what to do if the draft was already sent, so it stops short of full when/when-not guidance.

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