mailbox_reply

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

With no annotations, the description carries the behavioral burden. It does disclose a meaningful behavior: automatic routing to the original sender. However, it does not mention side effects, permission requirements, error behavior, or what happens if the thread or sender cannot be resolved.

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?

The description is a single concise sentence with no filler. The core action is front-loaded, and the auto-routing behavior is stated efficiently. It could earn a 5 only if it also briefly clarified the optional agent_id.

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 no annotations, no output schema, and no parameter descriptions, the description is too sparse to fully inform an agent. It fails to explain the role of agent_id, expected response, or failure modes, leaving the agent to guess on important invocation details.

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 0%, so the description must compensate. 'Reply to a message thread' implies msg_id identifies the thread and body contains the reply content, but the optional agent_id parameter is completely unexplained. The description provides only partial parameter understanding.

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 identifies the action ('Reply to a message thread') and the resource, and adds a distinguishing behavior ('Routes to the original sender automatically') that separates it from a generic send or broadcast tool. It doesn't explicitly name sibling tools, but the purpose is specific and 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 implies usage: reply to an existing thread rather than starting a new message. It gives enough context to infer when to use it versus mailbox_send or mailbox_broadcast, but it does not explicitly state when not to use it or name alternatives.

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