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

Annotations already declare it is a non-readOnly, non-destructive, non-openWorld operation. The description adds meaningful context beyond those hints: no actual phone call is placed, the operation is synthetic/offline, and the live trial path is retired, which helps set expectations about side effects.

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 short sentences, front-loaded with the core action and the most important constraint (synthetic_only must be true). Every clause earns its place and there is 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 mutation tool with six parameters, low schema description coverage, and no output schema, the description does not provide enough parameter guidance or alternative-tool routing. It explains what the tool does well, but an agent still lacks the detail needed to confidently populate the non-obvious optional fields.

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 17%, so the description should compensate for undocumented parameters, but it only mentions synthetic_only (already enforced as a const in the schema) and says nothing about pin, agent_id, project_id, or agent_endpoint_id. It leaves most parameter meaning to inference.

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 (Create) and a tightly scoped resource (offline synthetic trial call fixture), and immediately distinguishes itself from live call creation by noting it places no phone call and that live shared-number PIN trials are retired. An agent can tell this apart from create_outbound_call without opening either 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 context for use: synthetic_only must be true, the fixture is offline, and it places no phone call. It also implicitly excludes live PIN trial usage by saying those are retired, but it does not explicitly name alternatives such as create_outbound_call or simulation tools.

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