ClickHouse MCP Server

An MCP server for ClickHouse.

Features

ClickHouse Tools

run_query
Execute SQL queries on your ClickHouse cluster.
Input: query (string): The SQL query to execute.
Queries run in read-only mode by default (CLICKHOUSE_ALLOW_WRITE_ACCESS=false), but writes can be enabled explicitly if needed.

list_databases
List all databases on your ClickHouse cluster.

list_tables
List tables in a database with pagination.
Required input: database (string).
Optional inputs:
like / not_like (string): Apply LIKE or NOT LIKE filters to table names.
page_token (string): Token returned by a previous call for fetching the next page.
page_size (int, default 50): Number of tables returned per page.
include_detailed_columns (bool, default true): When false, omits column metadata for lighter responses while keeping the full create_table_query.
Response shape:
tables: Array of table objects for the current page.
next_page_token: Pass this value back to fetch the next page, or null when there are no more tables.
total_tables: Total count of tables that match the supplied filters.

chDB Tools

run_chdb_select_query
Execute SQL queries using chDB's embedded ClickHouse engine.
Input: query (string): The SQL query to execute.
Query data directly from various sources (files, URLs, databases) without ETL processes.

Health Check Endpoint

When running with HTTP or SSE transport, a health check endpoint is available at /health. This endpoint:

Returns 200 OK with the ClickHouse version if the server is healthy and can connect to ClickHouse
Returns 503 Service Unavailable if the server cannot connect to ClickHouse

Example:

bash

curl http://localhost:8000/health
# Response: OK - Connected to ClickHouse 24.3.1

Security

Authentication for HTTP/SSE Transports

When using HTTP or SSE transport, authentication is required by default. The stdio transport (default) does not require authentication as it only communicates via standard input/output.

Setting Up Authentication

1. Generate a secure token (can be any random string):

bash

# Using uuidgen (macOS/Linux)
   uuidgen

   # Using openssl
   openssl rand -hex 32

2. Configure the server with the token:

bash

export CLICKHOUSE_MCP_AUTH_TOKEN="your-generated-token"

3. Configure your MCP client to include the token in requests:

For Claude Desktop with HTTP/SSE transport:

json

{
     "mcpServers": {
       "mcp-clickhouse": {
         "url": "http://127.0.0.1:8000",
         "headers": {
           "Authorization": "Bearer your-generated-token"
         }
       }
     }
   }

For command-line tools:

bash

curl -H "Authorization: Bearer your-generated-token" http://localhost:8000/health

Development Mode (Disabling Authentication)

For local development and testing only, you can disable authentication by setting:

bash

export CLICKHOUSE_MCP_AUTH_DISABLED=true

WARNING: Only use this for local development. Do not disable authentication when the server is exposed to any network.

Configuration

This MCP server supports both ClickHouse and chDB. You can enable either or both depending on your needs.

1. Open the Claude Desktop configuration file located at:

On macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
On Windows: %APPDATA%/Claude/claude_desktop_config.json

2. Add the following:

json

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "uv",
      "args": [
        "run",
        "--with",
        "mcp-clickhouse",
        "--python",
        "3.10",
        "mcp-clickhouse"
      ],
      "env": {
        "CLICKHOUSE_HOST": "",
        "CLICKHOUSE_PORT": "",
        "CLICKHOUSE_USER": "",
        "CLICKHOUSE_PASSWORD": "",
        "CLICKHOUSE_ROLE": "",
        "CLICKHOUSE_SECURE": "true",
        "CLICKHOUSE_VERIFY": "true",
        "CLICKHOUSE_CONNECT_TIMEOUT": "30",
        "CLICKHOUSE_SEND_RECEIVE_TIMEOUT": "30"
      }
    }
  }
}

Update the environment variables to point to your own ClickHouse service.

Or, if you'd like to try it out with the ClickHouse SQL Playground, you can use the following config:

json

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "uv",
      "args": [
        "run",
        "--with",
        "mcp-clickhouse",
        "--python",
        "3.10",
        "mcp-clickhouse"
      ],
      "env": {
        "CLICKHOUSE_HOST": "sql-clickhouse.clickhouse.com",
        "CLICKHOUSE_PORT": "8443",
        "CLICKHOUSE_USER": "demo",
        "CLICKHOUSE_PASSWORD": "",
        "CLICKHOUSE_SECURE": "true",
        "CLICKHOUSE_VERIFY": "true",
        "CLICKHOUSE_CONNECT_TIMEOUT": "30",
        "CLICKHOUSE_SEND_RECEIVE_TIMEOUT": "30"
      }
    }
  }
}

For chDB (embedded ClickHouse engine), add the following configuration:

json

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "uv",
      "args": [
        "run",
        "--with",
        "mcp-clickhouse",
        "--python",
        "3.10",
        "mcp-clickhouse"
      ],
      "env": {
        "CHDB_ENABLED": "true",
        "CLICKHOUSE_ENABLED": "false",
        "CHDB_DATA_PATH": "/path/to/chdb/data"
      }
    }
  }
}

You can also enable both ClickHouse and chDB simultaneously:

json

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "uv",
      "args": [
        "run",
        "--with",
        "mcp-clickhouse",
        "--python",
        "3.10",
        "mcp-clickhouse"
      ],
      "env": {
        "CLICKHOUSE_HOST": "",
        "CLICKHOUSE_PORT": "",
        "CLICKHOUSE_USER": "",
        "CLICKHOUSE_PASSWORD": "",
        "CLICKHOUSE_SECURE": "true",
        "CLICKHOUSE_VERIFY": "true",
        "CLICKHOUSE_CONNECT_TIMEOUT": "30",
        "CLICKHOUSE_SEND_RECEIVE_TIMEOUT": "30",
        "CHDB_ENABLED": "true",
        "CHDB_DATA_PATH": "/path/to/chdb/data"
      }
    }
  }
}

3. Locate the command entry for uv and replace it with the absolute path to the uv executable. This ensures that the correct version of uv is used when starting the server. On a mac, you can find this path using which uv.

4. Restart Claude Desktop to apply the changes.

Optional Write Access

By default, this MCP enforces read-only queries so that accidental mutations cannot happen during exploration. To allow DDL or INSERT/UPDATE statements, set the CLICKHOUSE_ALLOW_WRITE_ACCESS environment variable to true. The server keeps enforcing read-only mode if the ClickHouse instance itself disallows writes.

Destructive Operation Protection

Even when write access is enabled (CLICKHOUSE_ALLOW_WRITE_ACCESS=true), destructive operations (DROP TABLE, DROP DATABASE, DROP VIEW, DROP DICTIONARY, TRUNCATE TABLE) require an additional opt-in flag for safety. This prevents accidental data deletion during AI exploration.

To enable destructive operations, set both flags:

json

"env": {
  "CLICKHOUSE_ALLOW_WRITE_ACCESS": "true",
  "CLICKHOUSE_ALLOW_DROP": "true"
}

This two-tier approach ensures that accidental drops are very difficult:

Write operations (INSERT, UPDATE, CREATE) require CLICKHOUSE_ALLOW_WRITE_ACCESS=true
Destructive operations (DROP, TRUNCATE) additionally require CLICKHOUSE_ALLOW_DROP=true

Running Without uv (Using System Python)

If you prefer to use the system Python installation instead of uv, you can install the package from PyPI and run it directly:

1. Install the package using pip:

bash

python3 -m pip install mcp-clickhouse

To upgrade to the latest version:

bash

python3 -m pip install --upgrade mcp-clickhouse

2. Update your Claude Desktop configuration to use Python directly:

json

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "python3",
      "args": [
        "-m",
        "mcp_clickhouse.main"
      ],
      "env": {
        "CLICKHOUSE_HOST": "",
        "CLICKHOUSE_PORT": "",
        "CLICKHOUSE_USER": "",
        "CLICKHOUSE_PASSWORD": "",
        "CLICKHOUSE_SECURE": "true",
        "CLICKHOUSE_VERIFY": "true",
        "CLICKHOUSE_CONNECT_TIMEOUT": "30",
        "CLICKHOUSE_SEND_RECEIVE_TIMEOUT": "30"
      }
    }
  }
}

Alternatively, you can use the installed script directly:

json

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "mcp-clickhouse",
      "env": {
        "CLICKHOUSE_HOST": "",
        "CLICKHOUSE_PORT": "",
        "CLICKHOUSE_USER": "",
        "CLICKHOUSE_PASSWORD": "",
        "CLICKHOUSE_SECURE": "true",
        "CLICKHOUSE_VERIFY": "true",
        "CLICKHOUSE_CONNECT_TIMEOUT": "30",
        "CLICKHOUSE_SEND_RECEIVE_TIMEOUT": "30"
      }
    }
  }
}

Note: Make sure to use the full path to the Python executable or the mcp-clickhouse script if they are not in your system PATH. You can find the paths using:

which python3 for the Python executable
which mcp-clickhouse for the installed script

Custom Middleware

You can add custom middleware to the MCP server without modifying the source code. FastMCP provides a middleware system that allows you to intercept and process MCP protocol messages (tool calls, resource reads, prompts, etc.).

How to Use

1. Create a Python module with middleware classes extending Middleware and a setup_middleware(mcp) function:

python

# my_middleware.py
import logging
from fastmcp.server.middleware import Middleware, MiddlewareContext, CallNext

logger = logging.getLogger("my-middleware")

class LoggingMiddleware(Middleware):
    """Log all tool calls."""
    
    async def on_call_tool(self, context: MiddlewareContext, call_next: CallNext):
        tool_name = context.message.name if hasattr(context.message, 'name') else 'unknown'
        logger.info(f"Calling tool: {tool_name}")
        result = await call_next(context)
        logger.info(f"Tool {tool_name} completed")
        return result

def setup_middleware(mcp):
    """Register middleware with the MCP server."""
    mcp.add_middleware(LoggingMiddleware())

2. Set the MCP_MIDDLEWARE_MODULE environment variable to the module name (without .py extension):

json

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "uv",
      "args": ["run", "--with", "mcp-clickhouse", "--python", "3.10", "mcp-clickhouse"],
      "env": {
        "CLICKHOUSE_HOST": "",
        "CLICKHOUSE_USER": "",
        "CLICKHOUSE_PASSWORD": "",
        "MCP_MIDDLEWARE_MODULE": "my_middleware"
      }
    }
  }
}

3. Ensure your middleware module is in Python's import path (e.g., in the same directory where the MCP server runs, or installed as a package).

Example Middleware

An example middleware module is provided in example_middleware.py showing common patterns:

Logging all MCP requests
Logging tool calls specifically
Measuring request processing time

To use the example:

json

"env": {
  "MCP_MIDDLEWARE_MODULE": "example_middleware"
}

Middleware Capabilities

The Middleware base class provides hooks for different MCP operations:

on_message(context, call_next) - Called for all messages
on_request(context, call_next) - Called for all requests
on_notification(context, call_next) - Called for all notifications
on_call_tool(context, call_next) - Called when a tool is executed
on_read_resource(context, call_next) - Called when a resource is read
on_get_prompt(context, call_next) - Called when a prompt is retrieved
on_list_tools(context, call_next) - Called when listing tools
on_list_resources(context, call_next) - Called when listing resources
on_list_resource_templates(context, call_next) - Called when listing resource templates
on_list_prompts(context, call_next) - Called when listing prompts

Each hook receives a MiddlewareContext object containing the message and metadata, and a call_next function to continue the pipeline.

Dynamic Client Configuration via Context State

Middleware can override ClickHouse client configuration on a per-request basis using the CLIENT_CONFIG_OVERRIDES_KEY context state key. The server merges these overrides with the base configuration from environment variables.

python

from fastmcp.server.dependencies import get_context
from mcp_clickhouse.mcp_server import CLIENT_CONFIG_OVERRIDES_KEY

ctx = get_context()
ctx.set_state(CLIENT_CONFIG_OVERRIDES_KEY, {
    "connect_timeout": 60,
    "send_receive_timeout": 120
})

This enables advanced use cases like dynamic timeout adjustments, tenant-specific routing, or per-user connection settings.

Development

1. In test-services directory run docker compose up -d to start the ClickHouse cluster.

2. Add the following variables to a .env file in the root of the repository.

*Note: The use of the default user in this context is intended solely for local development purposes.*

bash

CLICKHOUSE_HOST=localhost
CLICKHOUSE_PORT=8123
CLICKHOUSE_USER=default
CLICKHOUSE_PASSWORD=clickhouse

3. Run uv sync to install the dependencies. To install uv follow the instructions here. Then do source .venv/bin/activate.

4. For easy testing with the MCP Inspector, run fastmcp dev mcp_clickhouse/mcp_server.py to start the MCP server.

5. To test with HTTP transport and the health check endpoint:

bash

# For development, disable authentication
   CLICKHOUSE_MCP_SERVER_TRANSPORT=http CLICKHOUSE_MCP_AUTH_DISABLED=true python -m mcp_clickhouse.main

   # Or with authentication (generate a token first)
   CLICKHOUSE_MCP_SERVER_TRANSPORT=http CLICKHOUSE_MCP_AUTH_TOKEN="your-token" python -m mcp_clickhouse.main

   # Then in another terminal:
   # Without auth (if disabled):
   curl http://localhost:8000/health

   # With auth:
   curl -H "Authorization: Bearer your-token" http://localhost:8000/health

Environment Variables

The following environment variables are used to configure the ClickHouse and chDB connections:

ClickHouse Variables

##### Required Variables

CLICKHOUSE_HOST: The hostname of your ClickHouse server
CLICKHOUSE_USER: The username for authentication
CLICKHOUSE_PASSWORD: The password for authentication

[!CAUTION]
It is important to treat your MCP database user as you would any external client connecting to your database, granting only the minimum necessary privileges required for its operation. The use of default or administrative users should be strictly avoided at all times.

##### Optional Variables

CLICKHOUSE_PORT: The port number of your ClickHouse server
Default: 8443 if HTTPS is enabled, 8123 if disabled
Usually doesn't need to be set unless using a non-standard port
CLICKHOUSE_ROLE: The role to use for authentication
Default: None
Set this if your user requires a specific role
CLICKHOUSE_SECURE: Enable/disable HTTPS connection
Default: "true"
Set to "false" for non-secure connections
CLICKHOUSE_VERIFY: Enable/disable SSL certificate verification
Default: "true"
Set to "false" to disable certificate verification (not recommended for production)
TLS certificates: The package uses your operating system trust store for TLS certificate verification via truststore. We call truststore.inject_into_ssl() at startup to ensure proper certificate handling. Python’s default SSL behavior is used as a fallback only if an unexpected error occurs.
CLICKHOUSE_CONNECT_TIMEOUT: Connection timeout in seconds
Default: "30"
Increase this value if you experience connection timeouts
CLICKHOUSE_SEND_RECEIVE_TIMEOUT: Send/receive timeout in seconds
Default: "300"
Increase this value for long-running queries
CLICKHOUSE_DATABASE: Default database to use
Default: None (uses server default)
Set this to automatically connect to a specific database
CLICKHOUSE_MCP_SERVER_TRANSPORT: Sets the transport method for the MCP server.
Default: "stdio"
Valid options: "stdio", "http", "sse". This is useful for local development with tools like MCP Inspector.
CLICKHOUSE_MCP_BIND_HOST: Host to bind the MCP server to when using HTTP or SSE transport
Default: "127.0.0.1"
Set to "0.0.0.0" to bind to all network interfaces (useful for Docker or remote access)
Only used when transport is "http" or "sse"
CLICKHOUSE_MCP_BIND_PORT: Port to bind the MCP server to when using HTTP or SSE transport
Default: "8000"
Only used when transport is "http" or "sse"
CLICKHOUSE_MCP_QUERY_TIMEOUT: Timeout in seconds for SELECT tools
Default: "30"
Increase this if you see Query timed out after ... errors for heavy queries
CLICKHOUSE_MCP_AUTH_TOKEN: Authentication token for HTTP/SSE transports
Default: None
Required when using HTTP or SSE transport (unless CLICKHOUSE_MCP_AUTH_DISABLED=true)
Generate using uuidgen or openssl rand -hex 32
Clients must send this token in the Authorization: Bearer header
CLICKHOUSE_MCP_AUTH_DISABLED: Disable authentication for HTTP/SSE transports
Default: "false" (authentication is enabled)
Set to "true" to disable authentication for local development/testing only
WARNING: Only use for local development. Do not disable when exposed to networks
CLICKHOUSE_ENABLED: Enable/disable ClickHouse functionality
Default: "true"
Set to "false" to disable ClickHouse tools when using chDB only
CLICKHOUSE_ALLOW_WRITE_ACCESS: Allow write operations (DDL and DML)
Default: "false"
Set to "true" to allow DDL (CREATE, ALTER, DROP) and DML (INSERT, UPDATE, DELETE) operations
When disabled (default), queries run with readonly=1 setting to prevent data modifications
CLICKHOUSE_ALLOW_DROP: Allow destructive operations (DROP TABLE, DROP DATABASE, DROP VIEW, DROP DICTIONARY, TRUNCATE TABLE)
Default: "false"
Only takes effect when CLICKHOUSE_ALLOW_WRITE_ACCESS=true is also set
Set to "true" to explicitly allow destructive DROP and TRUNCATE operations
This is a safety feature to prevent accidental data deletion during AI exploration

Middleware Variables

MCP_MIDDLEWARE_MODULE: Python module name containing custom middleware to inject into the MCP server
Default: None (no middleware loaded)
Set to the module name (without .py extension) of your middleware module
The module must provide a setup_middleware(mcp) function
See Custom Middleware for details and examples

chDB Variables

CHDB_ENABLED: Enable/disable chDB functionality
Default: "false"
Set to "true" to enable chDB tools
CHDB_DATA_PATH: The path to the chDB data directory
Default: ":memory:" (in-memory database)
Use :memory: for in-memory database
Use a file path for persistent storage (e.g., /path/to/chdb/data)

Example Configurations

For local development with Docker:

env

# Required variables
CLICKHOUSE_HOST=localhost
CLICKHOUSE_USER=default
CLICKHOUSE_PASSWORD=clickhouse

# Optional: Override defaults for local development
CLICKHOUSE_SECURE=false  # Uses port 8123 automatically
CLICKHOUSE_VERIFY=false

For ClickHouse Cloud:

env

# Required variables
CLICKHOUSE_HOST=your-instance.clickhouse.cloud
CLICKHOUSE_USER=default
CLICKHOUSE_PASSWORD=your-password

# Optional: These use secure defaults
# CLICKHOUSE_SECURE=true  # Uses port 8443 automatically
# CLICKHOUSE_DATABASE=your_database

For ClickHouse SQL Playground:

env

CLICKHOUSE_HOST=sql-clickhouse.clickhouse.com
CLICKHOUSE_USER=demo
CLICKHOUSE_PASSWORD=
# Uses secure defaults (HTTPS on port 8443)

For chDB only (in-memory):

env

# chDB configuration
CHDB_ENABLED=true
CLICKHOUSE_ENABLED=false
# CHDB_DATA_PATH defaults to :memory:

For chDB with persistent storage:

env

# chDB configuration
CHDB_ENABLED=true
CLICKHOUSE_ENABLED=false
CHDB_DATA_PATH=/path/to/chdb/data

For MCP Inspector or remote access with HTTP transport:

env

CLICKHOUSE_HOST=localhost
CLICKHOUSE_USER=default
CLICKHOUSE_PASSWORD=clickhouse
CLICKHOUSE_MCP_SERVER_TRANSPORT=http
CLICKHOUSE_MCP_BIND_HOST=0.0.0.0  # Bind to all interfaces
CLICKHOUSE_MCP_BIND_PORT=4200  # Custom port (default: 8000)
CLICKHOUSE_MCP_AUTH_TOKEN=your-generated-token  # Required for HTTP/SSE

For local development with HTTP transport (authentication disabled):

env

CLICKHOUSE_HOST=localhost
CLICKHOUSE_USER=default
CLICKHOUSE_PASSWORD=clickhouse
CLICKHOUSE_MCP_SERVER_TRANSPORT=http
CLICKHOUSE_MCP_AUTH_DISABLED=true  # Only for local development!

When using HTTP transport, the server will run on the configured port (default 8000). For example, with the above configuration:

MCP endpoint: http://localhost:4200/mcp
Health check: http://localhost:4200/health

You can set these variables in your environment, in a .env file, or in the Claude Desktop configuration:

json

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "uv",
      "args": [
        "run",
        "--with",
        "mcp-clickhouse",
        "--python",
        "3.10",
        "mcp-clickhouse"
      ],
      "env": {
        "CLICKHOUSE_HOST": "",
        "CLICKHOUSE_USER": "",
        "CLICKHOUSE_PASSWORD": "",
        "CLICKHOUSE_DATABASE": "",
        "CLICKHOUSE_MCP_SERVER_TRANSPORT": "stdio",
        "CLICKHOUSE_MCP_BIND_HOST": "127.0.0.1",
        "CLICKHOUSE_MCP_BIND_PORT": "8000"
      }
    }
  }
}

Note: The bind host and port settings are only used when transport is set to "http" or "sse".

Running tests

bash

uv sync --all-extras --dev # install dev dependencies
uv run ruff check . # run linting

docker compose up -d test_services # start ClickHouse
uv run pytest -v tests
uv run pytest -v tests/test_tool.py # ClickHouse only
uv run pytest -v tests/test_chdb_tool.py # chDB only

Mcp Clickhouse

Documentation

ClickHouse MCP Server

Features

ClickHouse Tools

chDB Tools

Health Check Endpoint

Security

Authentication for HTTP/SSE Transports

Setting Up Authentication

Development Mode (Disabling Authentication)

Configuration

Optional Write Access

Destructive Operation Protection

Running Without uv (Using System Python)

Custom Middleware

How to Use

Example Middleware

Middleware Capabilities

Dynamic Client Configuration via Context State

Development

Environment Variables

ClickHouse Variables

Middleware Variables

chDB Variables

Example Configurations

Running tests

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