AI agents call users_discoverable_contacts_lookup to retrieve information from Slack without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool performs a straightforward user directory search indexed by email. It retrieves existing user metadata for Slack Connect discovery purposes without creating, modifying, deleting, or executing any operations. The blast radius of misuse is minimal: an attacker could enumerate users or confirm email addresses associated with Slack, but cannot access messages, modify data, or trigger external actions.
From the tool's definition Tool description states 'Look up a user by their email address' — a query operation that retrieves user information without modifying or executing side effects. The term 'lookup' and 'discovery' indicate read-only data retrieval.
Attacks that exploit this kind of access
Look up a user by their email address for Slack Connect discovery. It is categorised as a Read tool in the Slack MCP Server, which means it retrieves data without modifying state.
Register the Slack MCP server in PolicyLayer and add a rule for users_discoverable_contacts_lookup: 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 Slack. Nothing to install.
users_discoverable_contacts_lookup 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 users_discoverable_contacts_lookup 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 users_discoverable_contacts_lookup. 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.
users_discoverable_contacts_lookup is provided by the Slack MCP server (karbassi/slack-mcp). 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.
Teams ship this data inside their own products. See what a licence covers →