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

Goes well beyond the annotations: it discloses the label removal, the message.received webhook firing, task creation gated on verified-owner/allowlist sender-auth, that the suspicious label persists, that a repeat call returns 409 message_not_held without re-firing side effects, and the exact 404 cases. The auth requirement and the heuristic-not-guarantee caveat are also called out, which annotations cannot convey.

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?

It is fairly long for a two-parameter tool, but the trigger condition is front-loaded and the remaining sentences convey genuinely distinct facts (side effects, error codes, safety caveats) rather than padding. A slightly tighter grouping of the error cases would improve it, but nothing is wasted.

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?

With no output schema, the description fills the gap by describing the return payload (message with labels and safety), all relevant error outcomes (409 message_not_held, 404 inbox_not_found, 404 message_not_found), the side effects, and the trust caveat on the body. An agent has everything needed to call and interpret this tool correctly.

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 fully documented in the schema. The description restates inbox_id as 'inbox id, username, or email' and message_id as required, adding no syntax or constraint beyond the structured field descriptions; 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 (release), resource (a message held by inbound screening), and the precise condition that triggers it (screening held the message and a person decided it should be delivered). An agent can distinguish this from generic siblings like update_message or inject_inbound without opening a 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 opening sentence gives explicit when-to-use context tied to the 'held' label and a human decision, which is the correct selection signal. It does not name an alternative tool or state a when-not condition, but there is no obvious competing sibling for releasing a held message, so the context is sufficient without exclusions.

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