Check if a phone number is registered on WhatsApp. Use this before sending a message to a number not yet in your address book. Args: - phone: Phone number with country code, no spaces or dashes (e.g.,
AI agents call whatsapp_check_number to retrieve information from Waha without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool performs a lookup/query to determine registration status of a phone number. It has no side effects, does not modify data, does not execute code or commands, and does not delete or move resources. The stated use case ('Use this before sending a message') confirms it is a precursor check operation. This clearly falls under the Read category as it retrieves data without side effects.
From the tool's definition Tool description states: 'Check if a phone number is registered on WhatsApp.' This is a query operation that retrieves information about whether a number exists on the platform without modifying, executing operations, or causing side effects.
Attacks that exploit this kind of access
Check if a phone number is registered on WhatsApp. Use this before sending a message to a number not yet in your address book. Args: - phone: Phone number with country code, no spaces or dashes (e.g.,. It is categorised as a Read tool in the Waha MCP Server, which means it retrieves data without modifying state.
Register the Waha MCP server in PolicyLayer and add a rule for whatsapp_check_number: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Waha. Nothing to install.
whatsapp_check_number is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the whatsapp_check_number rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for whatsapp_check_number. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
whatsapp_check_number is provided by the Waha MCP server (@marcos-heidemann/waha-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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