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

Annotations already declare readOnly, idempotent, non-destructive, and the description is consistent with them. It adds genuinely useful behavior beyond annotations: the exclusion of already-recorded deliveries, the shouldSend gate, and the required follow-up recording step. It omits details like what the built message payload contains or how sinceVersion interactively filters, keeping it below 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?

Four short sentences, each carrying a distinct constraint: what is built, what is excluded, what gate controls sending, and who performs the actual send. Front-loaded with the core action and zero padding.

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, and the description helpfully surfaces shouldSend as the decision signal the agent must read. For a 3-parameter read-only builder with full annotation coverage, the main missing piece is the shape of the returned message/link and the meaning of sinceVersion.

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% across 3 parameters, so the description must compensate. It conveys the channel domain (WhatsApp/Signal/email) and hints that already-recorded deliveries can be excluded, which plausibly maps to sinceVersion, but eventId and the version semantics themselves are never explained. Partial compensation only.

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 gives a specific verb+resource: "Build a linked message" for WhatsApp, Signal or email, with a scope qualifier excluding already-recorded deliveries. An agent can distinguish it from record_channel_update and set_channels. It stops short of naming a sibling directly, so 4 rather than 5.

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?

Explicit when/how/when-not: gate sending on shouldSend being true, then send via "your authorized channel connector and record delivery afterwards." It also explicitly states what this tool does not do ("does not send anything"), leaving no ambiguity about the handoff to the delivery recorder.

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