ClickHouse/mcp-clickhouse

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.
  • Requires the optional chdb extra: pip install 'mcp-clickhouse[chdb]'

Health Check Endpoint

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

• Returns 200 OK (body: OK) if the server is healthy and can connect to ClickHouse
• Returns 503 Service Unavailable with a generic error message if the server cannot connect to ClickHouse

The endpoint is intentionally unauthenticated so orchestrator probes (e.g. Kubernetes liveness/readiness, load balancers) can reach it without credentials. The response body is deliberately minimal to avoid leaking backend version strings or error details; debug failures via the server logs.

Example:

curl http://localhost:8000/health
# Response: OK

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.

Three authentication modes are supported. Pick one:

Startup fails if none of these are configured for HTTP/SSE transports.

Setting Up Authentication

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

   # Using uuidgen (macOS/Linux)
   uuidgen
   
   # Using openssl
   openssl rand -hex 32
   

2. Configure the server with the token:

   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:

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

   Note: the /health endpoint is intentionally unauthenticated (see Health Check Endpoint above). To verify that bearer-token auth is actually rejecting unauthenticated requests, hit the MCP endpoint itself e.g. with the MCP Inspector, or by POSTing a JSON-RPC request to /mcp with and without the Authorization header and confirming the unauthenticated call returns 401.

OAuth / OIDC via FastMCP

For production deployments with identity providers (Azure Entra, Google, GitHub, WorkOS, etc.), delegate authentication to FastMCP's built-in auth providers instead of using a static token. Set FASTMCP_SERVER_AUTH to the full class path of a FastMCP auth provider, along with the provider-specific FASTMCP_SERVER_AUTH_* variables, and leave CLICKHOUSE_MCP_AUTH_TOKEN unset.

Example (Azure Entra):

export FASTMCP_SERVER_AUTH=fastmcp.server.auth.providers.azure.AzureProvider
export FASTMCP_SERVER_AUTH_AZURE_TENANT_ID="<tenant-id>"
export FASTMCP_SERVER_AUTH_AZURE_CLIENT_ID="<client-id>"
export FASTMCP_SERVER_AUTH_AZURE_CLIENT_SECRET="<client-secret>"

See the FastMCP docs for the full list of providers and their required environment variables.

Development Mode (Disabling Authentication)

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

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:

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "uv",
      "args": [
        "run",
        "--with",
        "mcp-clickhouse",
        "--python",
        "3.10",
        "mcp-clickhouse"
      ],
      "env": {
        "CLICKHOUSE_HOST": "<clickhouse-host>",
        "CLICKHOUSE_PORT": "<clickhouse-port>",
        "CLICKHOUSE_USER": "<clickhouse-user>",
        "CLICKHOUSE_PASSWORD": "<clickhouse-password>",
        "CLICKHOUSE_ROLE": "<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:

{
  "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:

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "uv",
      "args": [
        "run",
        "--with",
        "mcp-clickhouse[chdb]",
        "--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:

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "uv",
      "args": [
        "run",
        "--with",
        "mcp-clickhouse[chdb]",
        "--python",
        "3.10",
        "mcp-clickhouse"
      ],
      "env": {
        "CLICKHOUSE_HOST": "<clickhouse-host>",
        "CLICKHOUSE_PORT": "<clickhouse-port>",
        "CLICKHOUSE_USER": "<clickhouse-user>",
        "CLICKHOUSE_PASSWORD": "<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:

"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:

   python3 -m pip install mcp-clickhouse
   

   To install chDB support as well:

   python3 -m pip install 'mcp-clickhouse[chdb]'
   

   To upgrade to the latest version:

   python3 -m pip install --upgrade mcp-clickhouse
   

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

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "python3",
      "args": [
        "-m",
        "mcp_clickhouse.main"
      ],
      "env": {
        "CLICKHOUSE_HOST": "<clickhouse-host>",
        "CLICKHOUSE_PORT": "<clickhouse-port>",
        "CLICKHOUSE_USER": "<clickhouse-user>",
        "CLICKHOUSE_PASSWORD": "<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:

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "mcp-clickhouse",
      "env": {
        "CLICKHOUSE_HOST": "<clickhouse-host>",
        "CLICKHOUSE_PORT": "<clickhouse-port>",
        "CLICKHOUSE_USER": "<clickhouse-user>",
        "CLICKHOUSE_PASSWORD": "<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:

# 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):

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "uv",
      "args": ["run", "--with", "mcp-clickhouse", "--python", "3.10", "mcp-clickhouse"],
      "env": {
        "CLICKHOUSE_HOST": "<clickhouse-host>",
        "CLICKHOUSE_USER": "<clickhouse-user>",
        "CLICKHOUSE_PASSWORD": "<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:

"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.

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.

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:

   # 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:
   curl http://localhost:8000/health
   

Environment Variables

Configuration is split into independent groups. Mixing them up is a common cause of hard-to-debug connection failures:

[!IMPORTANT] Variables such as CLICKHOUSE_SECURE, CLICKHOUSE_VERIFY, and CLICKHOUSE_PORT apply to the ClickHouse database connection only. They do not configure TLS, ports, or auth for the MCP protocol endpoint.

Example: if the MCP server runs in Kubernetes behind an ingress that terminates TLS, that is an MCP transport concern. Keep CLICKHOUSE_SECURE aligned with how the pod reaches ClickHouse itself (HTTPS → true, plain HTTP → false). Setting CLICKHOUSE_SECURE=false because the MCP server is behind an ingress will make the server dial ClickHouse over HTTP—often against an HTTPS-only port—and produce opaque HTTP/TLS errors in the server logs.

ClickHouse database connection

These variables configure the clickhouse-connect HTTP client and the behavior of ClickHouse-backed tools such as run_query, list_databases, and list_tables.

Required Variables

• CLICKHOUSE_HOST: The hostname of your ClickHouse server (database endpoint, not the MCP server bind address)
• CLICKHOUSE_USER: The username for ClickHouse authentication
• CLICKHOUSE_PASSWORD: The password for ClickHouse 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: HTTP interface port of your ClickHouse server
  • Default: 8443 if CLICKHOUSE_SECURE=true, 8123 if CLICKHOUSE_SECURE=false
  • Usually doesn't need to be set unless using a non-standard port
  • Must be an HTTP interface port, not the native TCP protocol port used by clickhouse-client
  • Common values:
    • HTTP: 8123 (plain) / 8443 (TLS) — used by this server and ClickHouse Cloud HTTPS
    • Native TCP (not supported here): 9000 (plain) / 9440 (TLS) — used by clickhouse-client
  • If the server responds with Port 9000 is for clickhouse-client program, you are pointed at the native protocol; switch to the HTTP port (8123/8443 or your deployment's HTTP mapping)
• CLICKHOUSE_ROLE: The ClickHouse role to use for authentication
  • Default: None
  • Set this if your user requires a specific role
• CLICKHOUSE_SECURE: Enable HTTPS for the ClickHouse database connection (not for MCP clients)
  • Default: "true"
  • Set to "false" only when the MCP server reaches ClickHouse over plain HTTP (typical for local Docker Compose on port 8123)
  • Leave "true" for ClickHouse Cloud and any HTTPS database endpoint—even if the MCP server itself is exposed via HTTP, stdio, or an ingress that terminates TLS separately
  • Mismatching this flag with the database port (e.g. CLICKHOUSE_SECURE=false against port 8443) is a frequent setup mistake and usually surfaces as confusing HTTP client errors rather than a clear "wrong scheme" message
• CLICKHOUSE_VERIFY: Enable/disable SSL certificate verification for the ClickHouse HTTPS connection
  • 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_SERVER_HOST_NAME: Server hostname for SNI override and certificate validation on the ClickHouse connection
  • Default: None (uses the connection hostname)
  • This is useful when connecting through proxies or load balancers where the certificate hostname differs from the connection hostname. When set, this hostname will be used for both SNI (Server Name Indication) during the TLS handshake and for certificate hostname validation.
• CLICKHOUSE_PROXY_PATH: URL path prefix for the ClickHouse HTTP endpoint
  • Default: None
  • Set this when the ClickHouse HTTP interface is exposed behind a reverse proxy under a path prefix (for example, /clickhouse)
• CLICKHOUSE_CONNECT_TIMEOUT: Connection timeout in seconds for the ClickHouse client
  • Default: "30"
  • Increase this value if you experience connection timeouts
• CLICKHOUSE_SEND_RECEIVE_TIMEOUT: Send/receive timeout in seconds for the ClickHouse client
  • Default: "300"
  • Increase this value for long-running queries
• CLICKHOUSE_DATABASE: Default ClickHouse database to use
  • Default: None (uses server default)
  • Set this to automatically connect to a specific database
• CLICKHOUSE_ENABLED: Enable/disable ClickHouse database tools
  • Default: "true"
  • Set to "false" to disable ClickHouse tools when using chDB only
• CLICKHOUSE_ALLOW_WRITE_ACCESS: Allow write operations (DDL and DML) against ClickHouse
  • 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

MCP server and transport

These variables control the MCP process itself, including transport, authentication, and query-tool execution limits. They are independent of the ClickHouse database settings above. See also Authentication for HTTP/SSE Transports.

• 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.
  • stdio is typical for Claude Desktop; http/sse expose a network listener (bind host/port below)
• 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" — not related to CLICKHOUSE_HOST
• 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" — not related to CLICKHOUSE_PORT
• CLICKHOUSE_MCP_QUERY_TIMEOUT: Timeout in seconds for query tools
  • Default: "30"
  • Increase this if you see Query timed out after ... errors for heavy queries
• CLICKHOUSE_MCP_AUTH_TOKEN: Static bearer token for HTTP/SSE transports
  • Default: None
  • One of CLICKHOUSE_MCP_AUTH_TOKEN, FASTMCP_SERVER_AUTH, or CLICKHOUSE_MCP_AUTH_DISABLED=true is required for HTTP/SSE transports
  • Generate using uuidgen or openssl rand -hex 32
  • Clients must send this token in the Authorization: Bearer <token> header
• FASTMCP_SERVER_AUTH: Delegate authentication to a FastMCP auth provider
  • Default: None
  • Value is the full class path of an AuthProvider subclass, e.g. fastmcp.server.auth.providers.azure.AzureProvider or fastmcp.server.auth.providers.google.GoogleProvider
  • When set, FastMCP auto-loads the provider from its own FASTMCP_SERVER_AUTH_* environment variables; leave CLICKHOUSE_MCP_AUTH_TOKEN unset in this mode
• 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

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
  • Requires installing the optional extra: mcp-clickhouse[chdb]
• 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)

Common configuration pitfalls

• CLICKHOUSE_SECURE vs MCP / ingress TLS — Turning off CLICKHOUSE_SECURE because the MCP server sits behind Kubernetes ingress, a reverse proxy, or is reached over plain HTTP does not disable database TLS; it only changes how this process connects to ClickHouse. Configure ingress TLS separately from the database client settings.
• Native protocol ports — CLICKHOUSE_PORT must target ClickHouse's HTTP interface (8123/8443 by default). Ports 9000/9440 are for the native TCP protocol (clickhouse-client) and will not work with this server.
• Host confusion — CLICKHOUSE_HOST is the database hostname. CLICKHOUSE_MCP_BIND_HOST is only the address the MCP HTTP/SSE server listens on.

Example Configurations

For local development with Docker:

# 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:

# 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:

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

For chDB only (in-memory):

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

For chDB with persistent storage:

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

For MCP Inspector or remote access with HTTP transport:

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  # One auth mode required for HTTP/SSE (or FASTMCP_SERVER_AUTH, or CLICKHOUSE_MCP_AUTH_DISABLED=true)

For local development with HTTP transport (authentication disabled):

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:

{
  "mcpServers": {
    "mcp-clickhouse": {
      "command": "uv",
      "args": [
        "run",
        "--with",
        "mcp-clickhouse",
        "--python",
        "3.10",
        "mcp-clickhouse"
      ],
      "env": {
        "CLICKHOUSE_HOST": "<clickhouse-host>",
        "CLICKHOUSE_USER": "<clickhouse-user>",
        "CLICKHOUSE_PASSWORD": "<clickhouse-password>",
        "CLICKHOUSE_DATABASE": "<optional-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

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
CHDB_ENABLED=true uv run --extra chdb pytest -v tests/test_chdb_tool.py # chDB only

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