update_draft

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

The description discloses key behavioral details beyond annotations: 'omitted fields keep their current value' clarifies partial update semantics, and it specifies the unchangeability of the reply target and the constraint that sending drafts cannot be edited. With annotations already marking idempotentHint=true and destructiveHint=false, the description adds valuable context without contradicting them.

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 form the core description, with a third sentence providing key constraints. It's front-loaded with the primary action, followed by usage guidance and limitations. Every sentence adds important information without redundancy, though the last sentence could be slightly more concise.

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?

Given the tool's complexity (4 params, no output schema, no nested objects) and rich sibling set, the description is sufficiently complete. It covers the operation, parameters, constraints, and usage context. The only minor gap is that it doesn't explicitly state what happens on success (e.g., returns the updated draft), but the schema doesn't promise an output, so this is acceptable.

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. The description adds meaning by clarifying that omitted fields retain their current values, which maps directly to the optional parameters (to, text, subject). It also reiterates that the id is required. This semantic explanation goes beyond what the schema provides, earning a 4.

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 clearly states 'Edit the to, subject, or text of a draft', specifying the exact verb (edit) and resource (draft), and lists which fields can be changed. It distinguishes itself from siblings like 'create_draft' (which is for creating new drafts) and 'send_draft' (which sends rather than edits), making the purpose unambiguous.

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 explicitly tells when to use the tool: 'Call this when a draft needs changes, e.g. a human declined to approve it and you are revising it.' It also provides important exclusions: 'The reply target cannot be changed (create a new draft to reply to a different message)' and 'a draft that is already sending or sent can no longer be edited.' This offers excellent guidance on when not to use it and alternatives.

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