AI agents call search_messages to retrieve information from Claude Slack without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves or queries message data without creating, modifying, deleting, or executing any side effects. It falls squarely into the Read category. Severity is low because searching messages poses minimal risk; an AI agent could retrieve sensitive information if misconfigured, but the tool itself performs no destructive or dangerous operations.
From the tool's definition Tool performs a search operation across messages with no modification capability—'search' is a query/retrieval action. The description states it searches messages 'across channels and DMs', indicating read-only access to existing data.
Documented attack patterns abuse exactly the kind of access search_messages gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Claude Slack, and nothing reaches the server without passing your rules. This is the rule we recommend for search_messages:
{
"version": "1",
"default": "deny",
"tools": {
"search_messages": {}
}
}search_messages is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Search messages across channels and DMs. It is categorised as a Read tool in the Claude Slack MCP Server, which means it retrieves data without modifying state.
Register the Claude Slack MCP server in PolicyLayer and add a rule for search_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 Claude Slack. Nothing to install.
search_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 search_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 search_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.
search_messages is provided by the Claude Slack MCP server (theo-nash/claude-slack). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Claude Slack, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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19 Claude Slack tools catalogued and risk-classified — across an index of 43,000+ MCP servers.