create_reply_draft

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

Annotations already declare readOnlyHint=false, destructiveHint=false, and openWorldHint=true. The description adds genuinely non-obvious behavior: recipients, the 'Re:' subject, and the In-Reply-To/References headers are derived from the parent message, and no send occurs. It stops short of saying whether an existing draft is replaced or what is returned.

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, zero filler, with the core action and threading guarantee front-loaded and the non-send constraint last. Nothing could be cut without losing 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 7-parameter creation tool with no output schema, the description covers threading derivation, recipient derivation, and the non-send behavior, which is most of what an agent needs. It omits the return value (e.g., a draft ID for later update_draft/send_draft calls), which is the main remaining gap.

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 100%, so the baseline is 3. The description does add the concept that recipients are derived from the parent (which explains the optional 'to' override), but it adds no format or syntax detail beyond what the schema already documents per 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 specific verb and resource ('Create a draft reply to an existing email') and immediately qualifies it with 'threaded correctly', which separates it from create_draft, update_draft, and send_draft in the sibling set. An agent can identify the operation without opening the 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?

The closing 'Does not send' draws the boundary against send_draft/send_email, implying this is the right tool when a draft (not a sent message) is wanted. However, it never names the alternative tools or states prerequisites such as needing an existing emailId or an active connection.

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