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

Annotations already declare destructive, open-world, non-idempotent writes, and the description adds substantially more: the call is billed and rings real phones, the confirm gate exists to protect credit, the sandbox has no voice service, and the per-number queue status return. This is the kind of cost and side-effect context an agent needs before a destructive write.

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?

Opens with the WRITE marker and the core action, then layers cost, confirmation, environment limits, and return shape in dense, waste-free sentences. Every clause carries operational information.

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?

With no output schema, the description still tells the agent what comes back (per-number queue status), and it covers the billing, confirmation, and environment caveats. Nothing an agent needs in order to call this destructive write correctly is missing.

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 100%, so every parameter is already documented with format and constraints. The description reinforces 'up to 10 phone numbers' and that call_from must be an Africa's Talking voice number, but adds little beyond the schema. Baseline 3 is correct when the schema does the heavy lifting.

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 ('place an outbound voice call'), plus concrete scope ('from one of your Africa's Talking numbers to up to 10 phone numbers'). That is clearly distinguishable from the SMS, airtime, and mobile-data siblings without opening any 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 strong preconditions: confirm=true only after the user approved the numbers, and live apps only because the sandbox has no voice service. It also explains where the spoken content originates (the dashboard callback URL). It stops short of naming an explicit alternative when voice is unavailable, 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.