APIVerve

Phone Number Validator

PhoneNumberValidator

Read-only

Phone Number Validator: Phone Number Validator checks a phone number and returns whether it is valid, its line type, country, area and time zone, and the carrier its mobile range was allocated to. It flags disposable and VoIP numbers and outputs E.164, international, national and RFC3966 formats. (Cost: 10 credits)

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "number": "<number>"
    },
    "name": "PhoneNumberValidator"
  }
}

Input Schema

Name	Required	Description	Default
`number`	Yes	The phone number to validate
`country`	No	The two-letter country code of the phone number (e.g., us, uk). Optional when the number is in international format starting with +

Output Schema

Name	Required	Description
`data`	No
`error`	No	Error message, null on success
`status`	No	"ok" on success

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 7, 2026

TDQS

A3.9/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds value beyond them by disclosing the credit cost (10 credits), the breadth of the result set (carrier allocation, time zone, line type), the disposable/VoIP flagging, and the four output formats. It stops short of explaining failure behavior for malformed numbers, which keeps it at 4 rather than 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

One front-loaded paragraph that moves from purpose to results to cost with no filler. The return-field enumeration is somewhat redundant given an output schema exists, which costs it a point, but the sentence order is sensible and there is no fluff.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With annotations covering the safety profile, a full input schema, and an output schema, the description supplies what it must: scope, result breadth, flags, and cost. The remaining gap is the missing comparison against the disposable-only sibling, which is a usage-guidance issue rather than a completeness hole.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and both parameters are documented in the schema, including the rule that 'country' is optional when the number starts with '+'. The description adds no parameter-level meaning beyond that, so the baseline of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb and resource ('checks a phone number and returns whether it is valid') and enumerates the concrete payload: line type, country, area, time zone, carrier, disposable/VoIP flags, and four output formats. That is far more than a restatement of the name and lets an agent distinguish it from a narrow sibling like DisposablePhoneNumberChecker.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied by the stated scope but never made explicit: there is no 'use this when...' sentence, no exclusions, and no routing to alternatives such as DisposablePhoneNumberChecker for a pure disposability check. The cost note (10 credits) gives a weak signal that this is the heavier, full-validation option, but the agent must infer that.

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

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