Preview or send airtime

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

Annotations already declare the destructive/non-idempotent/open-world profile, and the description adds genuinely new operational context: server-side policy gates, a required user approval step, a configured currency/cap constraint, and an explicit 'never auto-retry' contract. These are exactly the traits an agent needs before triggering an irreversible send.

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 tight sentences with the default/opt-in behavior front-loaded, followed by prerequisites and the retry contract. No filler; each clause carries distinct 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?

For a destructive, non-idempotent mutation with no output schema, the description covers mode selection, gating, approval, amount format, currency/cap, and retry behavior. It does not describe the failure/response shape, a minor omission given annotations already flag the safety profile.

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 dryRun and currencyCode already documented in-schema. The description reinforces the dryRun semantics and adds a constraint not present in the schema — the configured cap on amounts — plus the 'exact recipients' targeting expectation, adding real value over the structured fields.

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 names a specific verb+resource (validate/preview vs. purchase/send airtime) and makes the default vs. dryRun=false distinction explicit, so an agent immediately knows this tool can both simulate and execute. It does not explicitly differentiate itself from the sibling at_send_sms, which is the only gap.

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 clearly states the default behavior (preview/validate) and the condition that flips it to a real send (dryRun=false plus server gates), and adds that user approval is required. This is strong context, though it never names a sibling or an explicit when-not-to-use-this alternative.

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