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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavioral context beyond the annotations: the `read` capability requirement and the key operational fact that the agent cannot send/release a held draft. It stops short of describing return/pagination behavior.

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 sentences, zero waste, front-loading the definition and triggers before the scoping and capability constraints. Every clause carries information the agent needs.

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 zero-required-parameter list tool with no output schema and full annotation coverage, the description supplies the essentials: what a draft is, scope, capability requirement, and the non-actionable release path. Only the return envelope's shape (fields, ordering) is left unstated, a minor 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%, with limit, status enum, and inbox_id all documented in the schema itself. The description adds only the scoping notion (token's customer and inbox set) but no format or syntax detail beyond what structured fields already provide, so baseline 3 applies.

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 (List) plus resource (sends held for human approval), and defines what qualifies as a draft with concrete triggers (external recipient on sandbox token, mode="draft"). This distinguishes it from siblings like get_draft (singular retrieve) and list_messages (non-held sends) without the agent needing to open either 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?

Explains the scope condition (token's customer and inbox set) and the lifecycle context (a human releases drafts out-of-band). However, it does not explicitly route the agent away from get_draft or list_messages, so the alternative-selection guidance is implied rather than stated.

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