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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is low, yet the description adds real context: the tool returns availableRecipients, unknown recipientIds are refused, and use is gated by mounting and actor safety ('when it is mounted and the current actor can safely use it'). The mounting/permission phrasing is a bit vague, keeping it from a 5.

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, but the second sentence runs long with an awkward clause ('when it is mounted and the current actor can safely use it') that is vague and hard to act on. Two dense sentences with some redundancy ('This tool writes nothing' repeated in the message schema).

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?

No output schema exists, yet the description explains the key return value (availableRecipients) and the refusal behavior, and annotations cover the safety profile. The workflow role relative to start_coordination_thread is conveyed, though the 'mounted' prerequisite remains underspecified.

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 baseline is 3, but the description adds meaning beyond the schema: recipientIds must be drawn from the returned availableRecipients and unknown IDs are refused, and it clarifies clientId omission for one's own household. This enriches the recipient/client semantics materially.

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 ('Prepare a new coordination-thread draft') and enumerates what the draft carries (member, recipients, subject, message). It is distinguishable from sibling drafts like draft_coordination_reply and draft_coordination_closeout, though it never explicitly contrasts itself with them.

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?

Gives clear sequencing guidance: call it before looking up a professional elsewhere, and note that it produces commit instructions for start_coordination_thread. It does not spell out when NOT to use it versus the other draft_* siblings, but the workflow placement is explicit.

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