Content
# ClickHouse MCP Server
<!-- mcp-name: io.github.ClickHouse/mcp-clickhouse -->
[](https://pypi.org/project/mcp-clickhouse)
An MCP server for ClickHouse.
<a href="https://glama.ai/mcp/servers/yvjy4csvo1"><img width="380" height="200" src="https://glama.ai/mcp/servers/yvjy4csvo1/badge" alt="mcp-clickhouse MCP server" /></a>
## 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](https://github.com/chdb-io/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:
```bash
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:
| Mode | When to use | Env var |
|----------------------------|-------------------------------------------|------------------------------------------------------------------------------------------------|
| Static bearer token | Simple deployments, internal services | `CLICKHOUSE_MCP_AUTH_TOKEN` |
| OAuth / OIDC (via FastMCP) | Azure Entra, Google, GitHub, WorkOS, etc. | `FASTMCP_SERVER_AUTH=<provider-class-path>` (+ provider-specific `FASTMCP_SERVER_AUTH_*` vars) |
| Disabled | Local development only | `CLICKHOUSE_MCP_AUTH_DISABLED=true` |
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):
```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"
}
}
}
}
```
Note: the `/health` endpoint is intentionally unauthenticated (see [Health Check Endpoint](#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](https://gofastmcp.com/servers/auth) 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):
```bash
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](https://gofastmcp.com/servers/auth) 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:
```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-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](https://sql.clickhouse.com/), 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[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:
```json
{
"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 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 require an additional opt-in flag for safety. The check covers any `DROP` statement (including the `ALTER TABLE ... DROP PARTITION` / `DROP PART` / `DROP COLUMN` clauses), any `TRUNCATE`, `DELETE` and `UPDATE` (both the lightweight statements and the `ALTER TABLE ... DELETE` / `ALTER TABLE ... UPDATE` mutations), `REPLACE TABLE`, `CREATE OR REPLACE`, `ALTER TABLE ... REPLACE PARTITION`, `ALTER TABLE ... CLEAR COLUMN` / `CLEAR INDEX` / `CLEAR PROJECTION`, and `DETACH ... PERMANENTLY`. Keywords inside string literals, quoted identifiers, and SQL comments are ignored, so they neither trigger the check nor hide a statement from it.
This check runs in the MCP server and is a best-effort guard against accidents. It is not a security boundary. The security boundary is the ClickHouse user's grants. Read-only mode (the default) is enforced server-side via `readonly=1`. The destructive-operation gate is not server-enforced.
For write mode, give the MCP server a dedicated ClickHouse user with only the privileges it needs:
```sql
CREATE USER mcp_agent IDENTIFIED BY '...';
GRANT SELECT, INSERT, CREATE TABLE, ALTER ADD COLUMN ON mydb.* TO mcp_agent;
```
Every statement outside these grants then fails server-side with `ACCESS_DENIED`, regardless of MCP flags. The server settings `max_table_size_to_drop` and `max_partition_size_to_drop` can also cap blast radius if pinned with settings constraints.
To enable destructive operations, set both flags:
```json
"env": {
"CLICKHOUSE_ALLOW_WRITE_ACCESS": "true",
"CLICKHOUSE_ALLOW_DROP": "true"
}
```
This two-tier approach makes accidental deletion difficult:
- **Write operations** (INSERT, CREATE, ALTER ADD COLUMN) require `CLICKHOUSE_ALLOW_WRITE_ACCESS=true`
- **Destructive operations** (DROP, TRUNCATE, DELETE, UPDATE, and the rest of the list above) 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 install chDB support as well:
```bash
python3 -m pip install 'mcp-clickhouse[chdb]'
```
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-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:
```json
{
"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:
```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-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:
```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.
The state value must be a dictionary. Nested `settings` and `generic_args` values must be
mappings and are merged with the base configuration. Invalid values fail the tool call before
a ClickHouse client is created. `CLICKHOUSE_ROLE` remains active unless the override explicitly
supplies `settings.role`. Top-level `role` and `ch_role` keys, plus the same keys under
`generic_args`, are rejected.
Treat these overrides as trusted middleware input. Middleware must authenticate and authorize
request-derived values before setting them. A per-request ClickHouse role is connection
configuration, not a tenant authorization boundary. Enforce tenant isolation with ClickHouse
users, roles, and grants.
## 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](https://docs.astral.sh/uv/). 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:
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:
| Group | Variables | Controls |
|-------|-----------|----------|
| **ClickHouse database connection** | `CLICKHOUSE_HOST`, `CLICKHOUSE_PORT`, `CLICKHOUSE_SECURE`, `CLICKHOUSE_VERIFY`, … | How **this MCP server** connects to your ClickHouse cluster over the **HTTP interface** |
| **MCP server / transport** | `CLICKHOUSE_MCP_*`, `FASTMCP_SERVER_AUTH`, `FASTMCP_SERVER_AUTH_*` | MCP transport, authentication, and query-tool execution limits |
| **Middleware / chDB** | `MCP_MIDDLEWARE_MODULE`, `CHDB_*` | Optional extensions |
> [!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](https://clickhouse.com/docs/en/integrations/python) 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 non-destructive DDL and DML (CREATE, INSERT, ALTER ADD COLUMN). Destructive statements additionally need `CLICKHOUSE_ALLOW_DROP=true`
* When disabled (default), queries run with `readonly=1` setting to prevent data modifications
* `CLICKHOUSE_ALLOW_DROP`: Allow destructive operations (any `DROP` or `TRUNCATE`, `DELETE` and `UPDATE` including the `ALTER TABLE` variants, `REPLACE TABLE` / `REPLACE PARTITION` / `CREATE OR REPLACE`, `CLEAR COLUMN` / `CLEAR INDEX` / `CLEAR PROJECTION`, and `DETACH ... PERMANENTLY`)
* Default: `"false"`
* Only takes effect when `CLICKHOUSE_ALLOW_WRITE_ACCESS=true` is also set
* This gate is a best-effort accident guard in the MCP server, not a security boundary. Restrict the ClickHouse user's grants for real enforcement (see [Destructive Operation Protection](#destructive-operation-protection))
#### 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](#authentication-for-httpsse-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](https://gofastmcp.com/servers/auth)
* 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](#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:
```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 # 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):
```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-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
```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
CHDB_ENABLED=true uv run --extra chdb pytest -v tests/test_chdb_tool.py # chDB only
```
## YouTube Overview
[](https://www.youtube.com/watch?v=y9biAm_Fkqw)
