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

Goes far beyond annotations: explains that account rules govern opt-in, reasons, quiet hours, per-day limits and budget, that refusals return {status: refused, why}, and that the call continues in the background and is billed at end. It also distinguishes blocking-until-answer from background continuation, which is exactly the behavioral context an agent needs for an openWorld, non-idempotent action.

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?

Front-loaded with the core action and trigger, then return statuses. Dense but nearly every clause carries information; the return-status enumeration is slightly compressed but earns its place.

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?

Even though an output schema exists, the description explains the return contract (answered/no_answer/busy/failed/insufficient, refused with why) and the async billing model, so an agent knows both what it gets back and what continues afterward. Complete for a call-placing tool.

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%, but the description still adds value by stating 'You never pass a number', enumerating reason values (done | blocked | decision), and clarifying that message (max 200 chars) 'opens the call'. It mostly echoes the schema's field docs, keeping it just below a 5.

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 ('Phone the human who owns this call on their own confirmed phone number') and clarifies the 'you never pass a number' constraint that separates it from a generic dialer. An agent can distinguish it from notify_me/say/activity without opening the 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?

Gives clear when-to-use triggers ('when a long task is done, you are stuck, or you need a decision and they are not on the call page'). It does not explicitly name when NOT to use it or point to the closest alternative (notify_me), so it falls short of a 5.

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