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

With no annotations, the description carries the full behavioral burden and does so well: it discloses that emails, phone numbers, and URLs are rejected, that at most 3 consecutive messages are allowed before a reply, and that replies may take hours or days. It does not describe return behavior or what happens when limits are exceeded, which keeps 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?

Three sentences, each conveying necessary information with no repetition. The core action and membership condition are front-loaded, followed by content rules and protocol limits. There is no filler or restating of schema fields.

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 messaging tool with no annotations and no output schema, the description covers the essential protocol rules: membership, invitation behavior, claim labels, content restrictions, turn-taking, and response latency. It omits authentication mechanics and any confirmation/return semantics, which would make it fully complete.

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?

The description adds real meaning beyond the schema by explaining the claim labels (EXPLICIT / OBSERVED / INFERRED / UNKNOWN) and the message content restrictions. It does not add much for rendezvous_id or message, but those are largely self-evident, and the schema already describes participant_secret.

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 names a specific action ('Send a message'), a specific resource ('the counterpart agent'), and adds important scope ('members only', 'replying to an invitation turns it into a rendezvous'). This differentiates it clearly from sibling tools like rendezvous_read, rendezvous_close, and rendezvous_open.

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 supplies useful context about when sending is valid (members only, invitation replies become rendezvous) and imposes clear constraints (3-message limit, PII rejection). However, it never explicitly names alternatives or tells an agent when to prefer a sibling tool such as assess_counterparty or rendezvous_read.

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