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

Annotations already convey mutating/destructive behavior (readOnlyHint=false, destructiveHint=true), so the description only needs to add context. It adds that the operation does not send and that replacement is revision-gated, which is useful, but it does not explain conflict handling or that the message field is a full replacement.

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?

The description is a single tight sentence with no filler. The core operation is front-loaded, and the revision requirement is stated precisely in the second clause.

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 destructive tool with a complex oneOf schema and an output schema, the description covers the essential selection decision: create vs. replace and no send. It leaves conflict semantics and idempotency behavior to the schema/annotations, which is acceptable given their detail.

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 high and every parameter already carries detailed descriptions, so the description does not need to repeat them. It adds no new meaning about parameters, which matches the baseline expectation for a fully documented schema.

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 states a specific action ('Create or replace a draft') and scopes it with 'without sending', which distinguishes it from send_email and other mail-sending siblings. It is immediately clear what resource is affected and what operation is performed.

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?

The description provides useful selection context by noting that replacement requires draftId and the current revision, implying creation is for new drafts. However, it does not explicitly name alternatives or state when save_draft should be preferred over list_drafts, send_email, or update_message.

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