Check if a field exists in a Redis hash. Args: name: The Redis hash key. key: The field name inside the hash. Returns: True if the field exists, False otherwise.
AI agents call hexists to retrieve information from Redis MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The hexists tool performs a read-only check on Redis hash data. It queries whether a field exists and returns a boolean result. No data is created, modified, deleted, or irreversibly changed. No code execution or financial transactions occur. This is a classic Read category operation with minimal blast radius if misused by an agent.
From the tool's definition Tool description states it 'Check if a field exists in a Redis hash' and 'Returns: True if the field exists, False otherwise.' This is a query operation with no side effects that only retrieves existence information without modifying data.
Documented attack patterns abuse exactly the kind of access hexists gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Redis MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for hexists:
{
"version": "1",
"default": "deny",
"tools": {
"hexists": {}
}
}hexists is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Check if a field exists in a Redis hash. Args: name: The Redis hash key. key: The field name inside the hash. Returns: True if the field exists, False otherwise. It is categorised as a Read tool in the Redis MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Redis MCP Server MCP server in PolicyLayer and add a rule for hexists: 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 Redis MCP Server. Nothing to install.
hexists 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 hexists 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 hexists. 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.
hexists is provided by the Redis MCP Server MCP server (redis/mcp-redis). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 53 Redis MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
53 Redis MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.