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

With no annotations, the description carries the full burden and does well: it discloses that this dials a real phone, the maximum call duration (2 min), the cost rate (25 credits/min), and the approval prerequisite. It stops short of describing the response or whether a recording/transcript results, but the safety-critical behavior is clear.

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?

Two sentences, front-loaded with the highest-risk fact ("DIALS A REAL PHONE") followed by constraints and cost. Every clause adds operational value with no filler.

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 high-impact real-phone action with no output schema, the description covers cost, duration, target restriction, and required preview/approval. It could say more about what the agent does on the call or what is returned, but it is sufficient to select and invoke the tool correctly.

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 only 33%: id is documented, but to_number and connection_id are not. The description compensates by declaring that to_number is the number dialed and restricting it to the user's own number, yet it leaves connection_id unexplained and does not specify a phone-number format.

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 opens with a specific, unambiguous action ("DIALS A REAL PHONE") and identifies both the target (to_number) and source (the channel's number). It explicitly distinguishes this from the related preview tool, so an agent can tell it apart from preview_phone_test_call without opening a 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?

It states clear preconditions: only call the user's own number, only after preview_phone_test_call, and only after explicit approval. These are explicit when-to-use and when-not-to-use rules, not implied guidance.

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