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

Goes well past the annotations: discloses that nothing is booked, sent or charged, that the code is valid 24 hours for up to 5 calls, the daily creation cap, and account requirements. This is consistent with destructiveHint=false while readOnlyHint=false correctly reflects that a sandbox resource is created.

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?

Purpose is front-loaded and the alternative follows immediately. The middle sentences run long ('Calling the number and keying the code reaches a phone assistant answering as the business you describe...') and the trailing return-key list is dense, but nearly every clause carries actionable 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?

Even without an output schema, the description enumerates the returned fields (sandbox, test_number, test_code, hear_url, expires_at, calls_allowed, how) and explains how the number and browser URL are used. Prerequisites, limits, and side-effect profile are all covered.

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 already 100%, yet the description adds semantic role that the schema does not: 'trade sets what the assistant knows to ask' and that area, hours, services and timezone 'shape what it says'. It also notes which fields are required, though per-parameter detail remains mostly in the schema.

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: 'Create a test call' to hear an After Hours answering line, and immediately clarifies 'it is not a real line'. It explicitly names the sibling set_up_answering_line as the tool for a production line, so an agent can distinguish the two 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 the use case (preview the assistant before anything is set up) and the exclusion (for a line on the business's own number use set_up_answering_line). It also states prerequisites (signed-in account, any permissions) and the quota boundary (3 test lines a day, rate limited).

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