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

Annotations declare the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=false), so the mutation nature is already known. The description goes beyond that by disclosing patch semantics — supplied fields replace saved values, recipient and attachment lists are replaced wholesale, omitted fields are preserved — which is exactly the behavior an agent needs and cannot get from the annotations. It does not address concurrency/conflict or invalid-ID handling, keeping it short of a 5.

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?

Two sentences, zero waste: purpose is front-loaded, then the replacement/preservation semantics follow. Every clause earns its place.

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?

An output schema exists, so return values need no explanation, and the annotations cover the safety profile. Combined with the patch-semantics sentence, an agent has enough to call it correctly; only auth requirements and failure behavior are unaddressed.

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 50%, so the description must carry weight, and it does: it explains that to/cc/bcc/attachments replace as a whole and that omitted fields stay unchanged, which is the single most consequential parameter behavior for this tool. This meaningfully compensates for the coverage gap, though it adds nothing about the remaining partially documented fields.

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 ('Edit an unsent draft'), and the 'unsent' qualifier usefully distinguishes it from sent-message siblings such as update_sent_message_labels and from send_draft. It is clear without needing the schema, though it does not name any sibling explicitly the way the top-tier examples do.

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?

Usage is only implied: the agent can infer this applies when modifying an already-saved, unsent draft. There is no explicit when-to-use vs. when-not, no named alternative (e.g. create_draft for new drafts, send_draft to send), and no stated prerequisites.

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