SMS Deliverability Check

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

Annotations already indicate readOnly, openWorld, idempotent, and non-destructive behavior. The description adds meaningful context: it performs a live line-type read, returns approximate local time, applies an 8am-9pm calling window, and explicitly excludes DNC/reassigned/litigator data. This goes beyond the structured annotations without contradicting them.

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 carry a clear value proposition, a summary of outputs, and an important limitation. The 'ONE verdict' opening is immediately meaningful, and there is no filler or redundancy.

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 single-parameter, read-only tool with an output schema, the description covers the decision-use case, key outputs, and a boundary of the tool's scope. The 8am-9pm window is specified, and because the output schema exists, exhaustively listing return fields is unnecessary. A brief note on error handling would round it out, but nothing critical is missing.

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?

The only parameter, phone_number, has 100% schema description coverage ('US/Canada number, any common format'). The description only restates the North American scope and adds no new parameter-level detail, so the baseline of 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?

The description states a specific purpose: a single verdict on whether a North American number can receive SMS and whether now is a reasonable time to send. It enumerates concrete outputs (sms_capable, VoIP flag, spam reputation, local time window) and explicitly distinguishes itself from legal-compliance tools. This makes it easy to separate from siblings like vri_spam_check or vri_number_lookup.

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 gives a clear use context ('for AI outreach') and an explicit exclusion ('not a legal compliance determination'). However, it never names alternative sibling tools or states when to choose this over vri_spam_check or vri_number_lookup, leaving the routing to implication rather than explicit guidance.

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