Hydrolix MCP Server

An MCP server for Hydrolix.

Tools

• run_select_query

  • Execute SQL queries on your Hydrolix cluster.
  • Input: sql (string): The SQL query to execute.

• list_databases

  • List all databases on your Hydrolix cluster.

• list_tables

  • List all tables in a database.
  • Input: database (string): The name of the database.

• get_table_info

  • Get table metadata such as schema
  • Input: database (string): The name of the database.
  • Input: table (string): The name of the table.

End-to-end tests

A separate suite under tests/e2e/ deploys the local working tree to a live Hydrolix Kubernetes cluster and smoke-tests the MCP tools against the running pod. It is excluded from default test runs and from the pre-push hook; running it requires explicit opt-in via the end_to_end pytest marker plus credentials. See tests/e2e/README.md for the runbook.

Quickstart

Get up and running in a few minutes. This section covers Claude Desktop and Claude Code.

Step 1 — Prerequisites

Before you begin, make sure you have:

• Hydrolix credentials — your cluster hostname plus either a username/password or a service account token. If you don't have these, ask your Hydrolix administrator.
• Claude Desktop — download from claude.ai/download.

Step 2 — Install the MCP server

Choose the method that matches your setup:

Option A: Using uv (recommended)

uv manages Python automatically and downloads mcp-hydrolix on demand, so no separate install step is needed. If you don't have uv, install it:

macOS / Linux:

curl -LsSf https://astral.sh/uv/install.sh | sh

Windows (PowerShell):

powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"

Option B: Using pip

Requires Python 3.13+. If you need to install Python, download it from python.org.

pip install mcp-hydrolix

Step 3 — Configure Claude Desktop

1. Open the Claude Desktop configuration file:

   • macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
   • Windows: %APPDATA%\Claude\claude_desktop_config.json
   • Linux: ~/.config/Claude/claude_desktop_config.json

2. Add the following entry to the "mcpServers" object (create the file with this content if it doesn't exist yet):

{
  "mcpServers": {
    "mcp-hydrolix": {
      "command": "uvx",
      "args": [
        "--python",
        "3.13",
        "--refresh-package",
        "mcp-hydrolix",
        "mcp-hydrolix"
      ],
      "env": {
        "HYDROLIX_URL": "https://<your-hydrolix-hostname>",
        "HYDROLIX_USER": "<your-username>",
        "HYDROLIX_PASSWORD": "<your-password>"
      }
    }
  }
}

Replace <your-hydrolix-hostname>, <your-username>, and <your-password> with your actual credentials.

[!NOTE] If you used Option B (pip), use "command": "mcp-hydrolix" with no "args" field instead.

[!TIP] If the file already has other entries, add the "mcp-hydrolix" block inside the existing "mcpServers" object rather than replacing the whole file.

[!NOTE] If you authenticate with a service account token instead of username/password, see Authentication.

Step 4 — Restart Claude Desktop

Restart the app to apply the configuration.

macOS / Windows users: Make sure to fully quit Claude before restarting. On macOS, press Cmd+Q or right-click the Dock icon and choose Quit. On Windows, use the system tray icon.

Step 5 — Verify it's working

1. Open a new conversation in Claude Desktop. Look for a tools/hammer icon near the text input — this confirms the MCP server connected successfully.

2. Try this prompt to confirm everything is working:

   Using your Hydrolix MCP tools, list the available databases.

Claude should call the list_databases tool and return a list of databases from your cluster.

Using Claude Code instead?

If you prefer the command line, make sure uv is installed (Option A from Step 2), then run:

claude mcp add --transport stdio hydrolix \
  --env HYDROLIX_URL=https://<your-hydrolix-hostname> \
  --env HYDROLIX_USER=<your-username> \
  --env HYDROLIX_PASSWORD=<your-password> \
  --env HYDROLIX_MCP_SERVER_TRANSPORT=stdio \
  -- uvx --python 3.13 --refresh-package mcp-hydrolix mcp-hydrolix

Then open Claude Code and test with the same prompt:

Using your Hydrolix MCP tools, list the available databases.

Using VS Code instead?

Click the Install in VS Code badge at the top of this README for a one-click install. If you prefer the UI flow, open the Command Palette (Cmd+Shift+P / Ctrl+Shift+P), run MCP: Add Server, choose Command (stdio), and reuse the uvx ... command and env block from Step 3.

Effective Usage

Due to the wide variety in LLM architectures, not all models will proactively use the tools above, and few will use them effectively without guidance, even with the carefully-constructed tool descriptions provided to the model. To get the best results out of your model while using the Hydrolix MCP server, we recommend the following:

• Refer to your Hydrolix database by name and request tool usage in your prompts (e.g., "Using MCP tools to access my Hydrolix database, please ...")
  • This encourages the model to use the MCP tools available and minimizes hallucinations.
• Include time ranges in your prompts (e.g., "Between December 5 2023 and January 18 2024, ...") and specifically request that the output be ordered by timestamp.
  • This prompts the model to write more efficient queries that take advantage of primary key optimizations

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 Hydrolix query-head's Clickhouse version if the server is healthy and can connect to Hydrolix
• Returns 503 Service Unavailable if the server cannot connect to the Hydrolix query-head

Example:

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

Configuration

The Hydrolix MCP server is configured using a standard MCP server entry. Consult your client's documentation for specific instructions on where to find or declare MCP servers. An example setup using Claude Desktop is documented below.

The recommended way to launch the Hydrolix MCP server is via the uv project manager, which will manage installing all other dependencies in an isolated environment.

Authentication

The server supports multiple authentication methods with the following precedence (highest to lowest):

1. Per-request Bearer token: Service account token provided via Authorization: Bearer <token> header
2. Per-request GET parameter: Service account token provided via ?token=<token> query parameter
3. Environment-based credentials: Credentials configured via environment variables
   • Service account token (HYDROLIX_TOKEN), or
   • Username and password (HYDROLIX_USER and HYDROLIX_PASSWORD)

When multiple authentication methods are configured, the server will use the first available method in the precedence order above. Per-request authentication is only available when using HTTP or SSE transport modes.

Note: Using a service account token with a readonly role is recommended.

MCP Server definition using username and password (JSON):

{
  "command": "uvx",
  "args": [
    "--python",
    "3.13",
    "--refresh-package",
    "mcp-hydrolix",
    "mcp-hydrolix"
  ],
  "env": {
    "HYDROLIX_URL": "https://<hydrolix-host>",
    "HYDROLIX_USER": "<hydrolix-user>",
    "HYDROLIX_PASSWORD": "<hydrolix-password>"
  }
}

MCP Server definition using service account token (JSON):

{
  "command": "uvx",
  "args": [
    "--python",
    "3.13",
    "--refresh-package",
    "mcp-hydrolix",
    "mcp-hydrolix"
  ],
  "env": {
    "HYDROLIX_URL": "https://<hydrolix-host>",
    "HYDROLIX_TOKEN": "<hydrolix-service-account-token>"
  }
}

MCP Server definition using username and password (YAML):

command: uvx
args:
- --python
- "3.13"
- --refresh-package
- mcp-hydrolix
- mcp-hydrolix
env:
  HYDROLIX_URL: https://<hydrolix-host>
  HYDROLIX_USER: <hydrolix-user>
  HYDROLIX_PASSWORD: <hydrolix-password>

MCP Server definition using service account token (YAML):

command: uvx
args:
- --python
- "3.13"
- --refresh-package
- mcp-hydrolix
- mcp-hydrolix
env:
  HYDROLIX_URL: https://<hydrolix-host>
  HYDROLIX_TOKEN: <hydrolix-service-account-token>

Configuration Example (Claude Desktop)

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 a mcp-hydrolix server entry to the mcpServers config block to use username and password:

{
  "mcpServers": {
    "mcp-hydrolix": {
      "command": "uvx",
      "args": [
        "--python",
        "3.13",
        "--refresh-package",
        "mcp-hydrolix",
        "mcp-hydrolix"
      ],
      "env": {
        "HYDROLIX_URL": "https://<hydrolix-host>",
        "HYDROLIX_USER": "<hydrolix-user>",
        "HYDROLIX_PASSWORD": "<hydrolix-password>"
      }
    }
  }
}

To leverage service account use the following config block:

{
  "mcpServers": {
    "mcp-hydrolix": {
      "command": "uvx",
      "args": [
        "--python",
        "3.13",
        "--refresh-package",
        "mcp-hydrolix",
        "mcp-hydrolix"
      ],
      "env": {
        "HYDROLIX_URL": "https://<hydrolix-host>",
        "HYDROLIX_TOKEN": "<hydrolix-service-account-token>"
      }
    }
  }
}

3. Update the environment variable definitions to point to your Hydrolix cluster.

4. (Recommended) Locate the command entry for uvx and replace it with the absolute path to the uvx executable. This ensures that the correct version of uvx is used when starting the server. You can find this path using which uvx or where.exe uvx.

5. Restart Claude Desktop to apply the changes. If you are using Windows, ensure Claude is stopped completely by closing the client using the system tray icon.

Configuration Example (Claude Code)

To configure the Hydrolix MCP server for Claude Code, run the following command:

claude mcp add --transport stdio hydrolix \
  --env HYDROLIX_USER=<hydrolix-user> \
  --env HYDROLIX_PASSWORD=<hydrolix-password> \
  --env HYDROLIX_URL=https://<hydrolix-host> \
  --env HYDROLIX_MCP_SERVER_TRANSPORT=stdio \
  -- uvx --python 3.13 --refresh-package mcp-hydrolix mcp-hydrolix

Environment Variables

The following variables are used to configure the Hydrolix connection. These variables may be provided via the MCP config block (as shown above), a .env file, or traditional environment variables.

Required Variables

You MUST set one of the following to identify the cluster:

• HYDROLIX_URL (recommended): The canonical public URL of your Hydrolix cluster, e.g. https://mycluster.hydrolix.live. For typical out-of-cluster deployments this single variable is sufficient — it supplies the host, port (scheme-default 443/80), and TLS settings for both the HTTP query endpoint and the REST /version probe.
• HYDROLIX_HOST (deprecated): The hostname of your Hydrolix server. Still honored for backwards compatibility but should be replaced by HYDROLIX_URL.

When HYDROLIX_MCP_SERVER_TRANSPORT is http or sse, HYDROLIX_URL specifically is required (the OAuth metadata endpoint advertises it). HYDROLIX_HOST alone is not sufficient for these transports.

Endpoint overrides

These override the values derived from HYDROLIX_URL. They are useful for in-cluster deployments where the HTTP query endpoint and the version-API live at different internal hostnames or ports. Override precedence: explicit new var > deprecated alias > HYDROLIX_URL-derived > hard default.

• HYDROLIX_HTTP_QUERY_HOST / HYDROLIX_HTTP_QUERY_PORT / HYDROLIX_HTTP_QUERY_SECURE: override the ClickHouse HTTP query endpoint.
• HYDROLIX_VERSION_API_HOST / HYDROLIX_VERSION_API_PORT / HYDROLIX_VERSION_API_SECURE: override the REST /version probe endpoint. HYDROLIX_VERSION_API_SECURE inherits from the resolved HTTP-query secure value by default.

Deprecated variables

The following are still honored during the transition window but will be removed in a future release. Migrate at your convenience:

External operators using any of these will see a one-time startup warning advising the migration to HYDROLIX_URL. In-cluster (o6r-managed) deployments will not see this warning; their migration is handled by the platform.

Authentication Variables

At least one authentication method must be configured when using the stdio transport:

• HYDROLIX_TOKEN: Service account token for environment-based authentication
• HYDROLIX_USER and HYDROLIX_PASSWORD: Username and password for environment-based authentication (both must be provided together)

In summary:

• For stdio, you MUST use HYDROLIX_TOKEN or HYDROLIX_USER+HYDROLIX_PASS (environmental credentials)
• For http/sse, you MAY use HYDROLIX_TOKEN or HYDROLIX_USER+HYDROLIX_PASS (environmental credentials), but you may instead use per-request credentials.

If no credentials are provided via the environment or the request, the request will fail.

Optional Variables

• HYDROLIX_VERIFY: Enable/disable SSL certificate verification
  • Default: "true"
  • Set to "false" to disable certificate verification (not recommended for production)
• HYDROLIX_DATABASE: Default database to use *Default: None (uses server default)
  • Set this to automatically connect to a specific database
• HYDROLIX_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.
• HYDROLIX_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"
• HYDROLIX_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"
• HYDROLIX_MAX_RAW_TIMERANGE: Maximum time range in seconds allowed for queries against non-summary tables
  • Default: 21600 (6 hours)
  • Queries targeting summary tables are not affected by this limit
• HYDROLIX_QUERY_POOL: Name of the Hydrolix query pool to route queries to (sets hdx_query_pool_name)
  • Default: None (uses the cluster's default query pool)
  • When set, every query the server issues is routed to the named pool; the pool must already exist on the cluster
  • In platform-managed (in-cluster) deployments the cluster tunable is mapped onto this same variable; the deployment owns the environment, so its value is authoritative
• HYDROLIX_HTTPS_PROXY / HYDROLIX_HTTP_PROXY: Outbound proxy for reaching the Hydrolix cluster
  • Default: None (connect directly)
  • Set one to route the connection through a corporate proxy; include the scheme, e.g. http://proxy.corp:8080. If both are set, HYDROLIX_HTTPS_PROXY wins
  • The standard HTTP_PROXY/HTTPS_PROXY environment variables are not used — the server needs these explicit HYDROLIX_-prefixed vars
  • This is the single egress proxy for all cluster traffic, including the internal /version capability probe; the proxy must permit that request, or the server silently falls back to non-parameterized queries
  • Note: this is unrelated to HYDROLIX_QUERIES_POOL_SIZE, which sizes the client-side query thread pool

For MCP Inspector or remote access with HTTP transport:

HYDROLIX_URL=https://my-cluster.hydrolix.net
HYDROLIX_USER=default
HYDROLIX_PASSWORD=myPassword
HYDROLIX_MCP_SERVER_TRANSPORT=http
HYDROLIX_MCP_BIND_HOST=0.0.0.0  # Bind to all interfaces
HYDROLIX_MCP_BIND_PORT=4200  # Custom port (default: 8000)

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

Using Per-Request Authentication with HTTP Transport

When using HTTP or SSE transport, you can omit environment-based credentials and instead provide authentication per-request. This is useful for multi-user scenarios or with clients that don't support running MCP servers locally.

Example mcpServers configuration connecting to a remote HTTP server with per-request authentication:

{
  "mcpServers": {
    "mcp-hydrolix-remote": {
      "url": "https://my-hydrolix-mcp.example.com/mcp?token=<service-account-token>"
    }
  }
}

Example minimal .env configuration for running your own HTTP server without environment credentials:

HYDROLIX_URL=https://my-cluster.hydrolix.net
HYDROLIX_MCP_SERVER_TRANSPORT=http

Though not part of the MCP specification, many MCP clients allow adding headers to MCP-issued requests. When this is possible, we recommend configuring the MCP client to pass a service account token via the Authorization: Bearer <sa-token-here> header instead of as a query parameter for greater security.

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