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:

Related MCP server: MCP Alchemy

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):

   # 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" } } } }

   For command-line tools:

   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:

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:

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:

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

You can also enable both ClickHouse and chDB simultaneously:

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:

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 upgrade to the latest version:

   python3 -m pip install --upgrade mcp-clickhouse

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

Alternatively, you can use the installed script directly:

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:

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

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:

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.

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

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: # 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

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 <token> 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:

For ClickHouse Cloud:

For ClickHouse SQL Playground:

For chDB only (in-memory):

For chDB with persistent storage:

For MCP Inspector or remote access with HTTP transport:

For local development with HTTP transport (authentication disabled):

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:

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

Running tests

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