Hydrolix MCP Server

An MCP server for Hydrolix.

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.

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.

Tools

• run_select_query

  • Execute SQL queries on your Hydrolix cluster.
  • Input: query (string): The SQL query to execute.
  • Input: max_cells (integer, optional): Result cell budget (rows × columns); when the server sets a cap, a caller can only lower it.
  • Input: purpose (string, required): Why the query is being run; recorded with the query as hdx_query_comment.
  • A trailing FORMAT clause is removed; the server selects the wire format.

• 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.

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. The ?token= form exists for clients that cannot send headers; set HYDROLIX_ALLOW_TOKEN_QUERY_PARAM=false on deployments where every client sends the Authorization header (see Per-request credentials).

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 (a forthcoming OAuth metadata endpoint would advertise it). HYDROLIX_HOST alone is not sufficient for these transports.

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.

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".

Optional Variables

See docs/CONFIG.md for endpoint overrides, deprecated variable aliases, and the full set of optional tuning variables (timeouts, query SETTINGS overrides, result truncation, HTTP/SSE worker tuning, proxy, metrics, and escape hatches).

Maintainers

Tasks that need operational privileges — running the end-to-end suite against a live Hydrolix cluster, and cutting a release — are documented separately in MAINTAINERS.md.