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How to block unsafe Cypher queries in the Neo4j MCP server

To block unsafe Cypher queries in the Neo4j MCP server, guard the driver passed to create_mcp_server() in mcp-neo4j-cypher. Blocked queries raise GuardError and are never sent.

Install​

pip install neo4j-guard mcp-neo4j-cypher

Guard the driver​

Save this as server.py. The server's get_neo4j_schema tool calls apoc.meta.schema, so allow it.

import asyncio

from mcp_neo4j_cypher.server import create_mcp_server
from neo4j import AsyncGraphDatabase
from neo4j_guard import guard


async def main() -> None:
    driver = guard(
        AsyncGraphDatabase.driver("neo4j://localhost:7687", auth=("neo4j", "password")),
        allow=["apoc.meta.schema"],
    )
    await create_mcp_server(driver, read_only=True).run_stdio_async()


asyncio.run(main())

Add the server to the MCP client​

Run server.py instead of the mcp-neo4j-cypher command:

{
  "mcpServers": {
    "neo4j": {
      "command": "python",
      "args": ["/path/to/server.py"]
    }
  }
}

Compare with read_only​

The server's read_only option removes the write_neo4j_cypher tool and rejects queries that Neo4j classifies as writes. The guarded driver also blocks:

  • APOC and other procedures, except entries in allow.
  • LOAD CSV, which reads files and URLs.
  • Labels and properties in disallow, in queries and in returned records.