signal_get_chat_messages
AI agents call signal_get_chat_messages to retrieve information from Signal without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves historical Signal messages from a chat, which is a read-only operation with no data modification. Severity is medium rather than low because Signal messages may contain sensitive personal communications, and unauthorized access by an AI agent could expose private conversations, though there is no destructive or financial impact.
From the tool's definition Tool name 'signal_get_chat_messages' combined with server description stating 'retrieving Signal messages' and sibling tools 'signal_list_chats' and 'signal_search_chat' indicate this is a retrieval operation.
Documented attack patterns abuse exactly the kind of access signal_get_chat_messages gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Signal, and nothing reaches the server without passing your rules. This is the rule we recommend for signal_get_chat_messages:
{
"version": "1",
"default": "deny",
"tools": {
"signal_get_chat_messages": {}
}
}signal_get_chat_messages is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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signal_get_chat_messages. It is categorised as a Read tool in the Signal MCP Server, which means it retrieves data without modifying state.
Register the Signal MCP server in PolicyLayer and add a rule for signal_get_chat_messages: 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 Signal. Nothing to install.
signal_get_chat_messages 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 signal_get_chat_messages 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 signal_get_chat_messages. 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.
signal_get_chat_messages is provided by the Signal MCP server (stefanstranger/signal-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Signal, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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3 Signal tools catalogued and risk-classified — across an index of 43,000+ MCP servers.