Return {"exists": true|false} for a given email.
AI agents call user_exists to retrieve information from Database MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool performs a query operation that retrieves information about whether a user exists without creating, modifying, or deleting any data. It is a straightforward lookup with no side effects, fitting the 'Read' category.
From the tool's definition Tool returns a boolean result for a given email with no side effects. Description explicitly states it checks existence without modification: 'Return {"exists": true|false} for a given email.'
Attacks that exploit this kind of access
Return {"exists": true|false} for a given email. It is categorised as a Read tool in the Database MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Database MCP Server MCP server in PolicyLayer and add a rule for user_exists: 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 Database MCP Server. Nothing to install.
user_exists 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 user_exists 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 user_exists. 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.
user_exists is provided by the Database MCP Server MCP server (vrushil1/database-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.
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