wwebjs-mcp

client_getNumberId

Retrieve the registered WhatsApp ID for a phone number, returning null if the number is not on WhatsApp.

Instructions

[Client] Get the registered WhatsApp ID for a number. Return null if the number is not registered on WhatsApp

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": {
      "sessionId": "<sessionId>"
    },
    "name": "client_getNumberId"
  }
}

Input Schema

Name	Required	Description	Default
`number`	No	The number or ID ('@c.us' will be automatically appended if not specified)
`sessionId`	Yes	Unique identifier for the session (alphanumeric and - allowed)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Aug 2, 2026

TDQS

A4/5.0

Behavior4/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It explicitly states a key behavior: returning null if the number is not registered on WhatsApp. It also implies a read-only operation via 'Get'. This goes beyond the schema, which only describes parameters.

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?

The description is a single, concise sentence with a clear subject and outcome. It is front-loaded with '[Client]' for grouping and quickly conveys the core purpose. No unnecessary words or repetition.

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?

Given the simplicity of the tool (2 well-documented parameters, no output schema), the description adequately explains the return behavior (registered ID or null). It is complete enough for an AI agent to invoke the tool correctly, though it doesn't detail the exact format of the returned ID or potential errors.

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%, with both 'number' and 'sessionId' fully described in the input schema. The description adds no additional parameter information beyond what's already present, so it doesn't compensate further. Baseline of 3 is appropriate.

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 clearly states the tool's function: getting the registered WhatsApp ID for a number. It distinguishes itself from sibling tools like client_getFormattedNumber (formatting only) and client_isRegisteredUser (likely returns a boolean) by specifying the return of the ID and the null condition for unregistered numbers.

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?

The description implies usage: use this when you need the registered WhatsApp ID for a phone number. However, it does not explicitly mention when to use this versus alternatives, nor any exclusions or prerequisites. Sibling tools like client_getContactById or client_isRegisteredUser are not referenced.

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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