API Ninjas

phoneLookup

Read-only

Returns carrier, line type, VOIP status and MCC/MNC for a phone number, with optional country. For format and validity checks only use /validatephone.

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": "phoneLookup"
  }
}

Input Schema

Name	Required	Description	Default
`number`	Yes	Phone number to look up. The leading '+' is optional. If country is not set, include the country code (e.g. 12065550100 or +12065550100).
`country`	No	2-letter ISO-3166 country code the phone number belongs to.

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 9, 2026

TDQS

A4/5.0

Behavior3/5

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

Annotations declare readOnlyHint=true, so the safe-read profile is already known. The description adds the output fields (carrier, line type, VOIP, MCC/MNC), which is useful context about what the lookup yields, but it doesn't cover rate limits, data freshness, or error behavior. With annotations carrying the safety burden, a 3 is appropriate.

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

Conciseness5/5

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

Two tight sentences, zero waste. The exclusion guidance is front-loaded right after the output fields, so the agent knows immediately when to route elsewhere.

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?

For a read-only lookup with full schema coverage, no output schema, and annotations declaring safety, the description is nearly complete: it states inputs, outputs, and the exclusion. Only minor gaps remain (no return format or error semantics), but nothing an agent needs to call it correctly is missing.

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%, so both parameters are fully documented in the schema (including the note about country code when country is omitted). The description adds no parameter syntax or format details beyond what the schema already provides. Baseline 3 is correct when the schema does all the work.

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

Purpose4/5

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

Clear verb 'Returns' plus specific resources (carrier, line type, VOIP status, MCC/MNC) and the input resource 'phone number'. Distinguishes from validatePhone by pointing to it, but the sibling list is huge and phone-network-intelligence siblings like getCountryData or binLookup aren't referenced. Nonetheless the purpose is unambiguous.

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

Usage Guidelines5/5

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

Explicitly states when NOT to use this tool: 'For format and validity checks only use /validatephone.' This directly names the alternative tool and the condition that selects it, leaving nothing to inference.

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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