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

Annotations already declare destructive=true, idempotent=true, and readOnly=false, so the safety profile is covered and 'replace' is consistent with them. The description adds input-format behavior ('plain text is fine; line breaks are kept'), which is useful but modest; it says nothing about failure modes or what happens to a non-existent draftId.

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 tight sentences, front-loaded with the action, followed by prerequisite and format note. No filler; every sentence carries information.

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 3-param mutation with annotations covering safety and no output schema, the description covers purpose, prerequisite, and input format adequately. Only missing edge-case behavior (invalid/absent draftId) keeps it from a 5.

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 all three parameters are documented in the schema, so the schema does the heavy lifting. The description names subject and body and the source of draftId, and adds the plain-text/line-break note relevant to body, but nothing beyond baseline.

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: 'Replace the subject and body of one draft that has not been sent.' The 'not been sent' scope cleanly separates it from send_reply and discard_draft, though no sibling is named 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 a concrete prerequisite: 'Get the draftId from list_pending_drafts.' This routes the agent to the right sibling for the ID. No when-not-to-use or exclusion guidance, so it stops short of a 5.

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