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

With no annotations, the description carries the burden and does well: it discloses that no call is placed, gives a price (25 credits/min) and a hard duration cap (2 min). It stops short of saying whether the preview itself bills credits or what the response contains.

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 short sentences, front-loaded result then safety then directive. Only the awkward 'from which' clause costs it a point.

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 and no annotations mean the description should be fully self-sufficient. It covers safety and pricing but never states what the preview returns (the resolved from/to numbers, projected credit spend) or what happens if connection_id is omitted.

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 67%, with the agent id and E.164 number documented in the schema but connection_id undocumented. The description gestures at the 'from which' connection but adds no format or sourcing guidance beyond what the schema already says. Baseline 3 is appropriate.

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?

Names the action and the resource (a phone test-call preview) and states what it returns: the caller/callee pairing and the cost. However, the phrase 'which number would be called from which' is garbled, leaving the direction of the call slightly ambiguous.

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?

'ALWAYS call first' plus 'Nothing is dialled' gives a clear when-to-use rule relative to the actual dialling step. The counterpart tool (phone_test_call) is never named, so the agent must infer which sibling this precedes.

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