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

Far exceeds the annotations (readOnlyHint=false, destructiveHint=false, idempotentHint=false). It discloses concrete state changes (thread returns to replied, sequence steps stop, contact becomes emailable again), the guard behavior including the exact error payload shape, and the dashboard-equivalent guardrail limit.

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?

Purpose is front-loaded and the sentence that follows adds genuine constraints rather than filler. The parenthetical examples and guardrail sentence make it dense, but every sentence carries operative 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 mutating tool with no output schema, it explains side effects, scoping limits, and the approval error response. The success return payload is not described, but the state consequences are, which is the more important gap to close here.

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 both parameters are already documented, and the description goes further by explaining the two-step approval_token contract (first call returns approval_required with a token, second call uses it after user confirmation). That adds real meaning beyond the format string.

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 with unusual precision: "Undo an opt-out the reply reading recorded on a thread," including the motivating case (a misread such as "remove me as the contact"). No sibling tool does anything comparable, so the agent can distinguish it immediately.

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?

Explicitly bounds when the tool applies and when it does not: only opt-outs this account's reply reading listed are removed, while an unsubscribe-link click or another sender's opt-out stays. It also outlines the approval flow, though it names no alternative tool for the excluded cases.

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