MCP ClickHouse Tool

A read-only Model Context Protocol (MCP) server for ClickHouse that supports metadata discovery, resources, parameterized SELECT queries, SHOW introspection, query analysis, and snapshot mode for large result sets, with profile-based configuration and strict no-DML/DDL enforcement.

Requirements: Python 3.13+, a running ClickHouse instance, and connection details via environment variables or a config file.

Quick start

Set a DSN and run the server with MCP Inspector:

# Option 1: Run directly with uvx (no clone needed)
export MCP_CLICKHOUSE_DSN="http://default:@localhost:8123/default"
npx -y @modelcontextprotocol/inspector uvx mcp-clickhousex

# Option 2: Run from source (clone repo, then)
export MCP_CLICKHOUSE_DSN="http://default:@localhost:8123/default"
npx -y @modelcontextprotocol/inspector uv run main.py

Configuration

All settings use the MCP_CLICKHOUSE prefix. Flat environment variables (e.g. MCP_CLICKHOUSE_DSN) are the straightforward way to configure the default profile when you have a single connection. For multiple profiles, the user-scoped config.json file is recommended.

Single connection: Configure via environment variables.

# Connection DSN (required).
export MCP_CLICKHOUSE_DSN="http://user:password@host:8123/database"

# Optional description for the default profile (tooling/AI discovery).
export MCP_CLICKHOUSE_DESCRIPTION="Primary cluster"

# Optional max rows per interactive query (default 500; hard ceiling 1000).
export MCP_CLICKHOUSE_QUERY_MAX_ROWS="500"

# Optional interactive query timeout in seconds (default 30; hard ceiling 300).
export MCP_CLICKHOUSE_QUERY_COMMAND_TIMEOUT_SECONDS="30"

# Optional max rows for snapshot queries (default 10000; hard ceiling 50000).
export MCP_CLICKHOUSE_SNAPSHOT_MAX_ROWS="10000"

# Optional snapshot query timeout in seconds (default 120; hard ceiling 300).
export MCP_CLICKHOUSE_SNAPSHOT_COMMAND_TIMEOUT_SECONDS="120"

Multiple connections: Use the user-scoped config.json file (recommended). Env vars also work via the MCP_CLICKHOUSE_PROFILES_<NAME>_ prefix (e.g. MCP_CLICKHOUSE_PROFILES_WAREHOUSE_DSN).

• Unix-like: ~/.config/mcp-clickhousex/config.json
• Windows: %USERPROFILE%\.config\mcp-clickhousex\config.json

Example (config.json):

{
  "profiles": {
    "default": {
      "dsn": "http://default:@localhost:8123/default",
      "description": "Primary",
      "query_max_rows": 500,
      "query_command_timeout_seconds": 60,
      "snapshot_max_rows": 10000,
      "snapshot_command_timeout_seconds": 120
    },
    "warehouse": {
      "dsn": "http://user:pass@warehouse:8123/analytics",
      "description": "Warehouse"
    }
  }
}

Special characters in credentials: If the username or password contains URL-reserved characters, percent-encode them in the DSN:

Character	Encoding
#	%23
?	%3F
/	%2F
@	%40
%	%25

For example, username admin@org and password p#ss? become admin%40org:p%23ss%3F in the DSN: http://admin%40org:p%23ss%3F@host:8123/database.

Tools

Tool descriptions match server.py tool docstrings except the [ClickHouse] prefix is omitted here (it remains in MCP-exposed metadata). Parameter text matches each Field(description=…) on the same tool.

Tool	Description	Key params
list_profiles	List configured profiles. Each entry includes name and optional description.	—
get_cluster_properties	Get cluster properties and execution limits. Returns ClickHouse server version plus enforced limits (max rows, timeouts) for the profile.	profile — Profile name; uses default profile when omitted. Src: profiles.
run_query	Execute read-only SELECT or WITH … SELECT. One statement; DML, DDL, SET, SYSTEM, and similar are rejected. Returns {data, row_count} where data is an RFC 4180 CSV string. Pass snapshot=true to persist the result to disk and receive {snapshot_uri, row_count} instead; fetch the CSV via the snapshot resource URI. Max-rows cap; overflow sets truncated and row_limit. Same SQL validation as analyze_query.	sql (required) — Read-only SELECT or WITH … SELECT. One statement; use qualified db.table or database. Driver placeholder syntax for parameters. parameters — Named parameters for driver placeholders (e.g. %(name)s or {name:Type}). database — Session default database for unqualified names. Src: databases. profile — Profile name; uses default profile when omitted. Src: profiles. snapshot — When true, persist the full result as a CSV file and return a resource URI (chx://snapshots/{id}) instead of inline data. Use for queries that may exceed the interactive row limit (1 000). Snapshot limits apply (default 10 000 rows, hard ceiling 50 000). Entries expire after 7 days.
run_show	Execute SHOW introspection statement. One statement per call; INTO OUTFILE rejected. Interactive row limits apply (default 500, hard ceiling 1 000). Same timeout as run_query.	sql (required) — Single SHOW statement (e.g. SHOW DATABASES, SHOW CREATE TABLE). No INTO OUTFILE. parameters — Named parameters for driver placeholders (e.g. %(name)s or {name:Type}). database — Session default database for unqualified names. Src: databases. profile — Profile name; uses default profile when omitted. Src: profiles.
analyze_query	Explain read-only SELECT or WITH … SELECT. Returns plan, pipeline, and/or syntax text. Default types plan and pipeline. Uses query timeout and optional database; no max-rows cap unlike run_query.	sql (required) — Read-only SELECT or WITH … SELECT for EXPLAIN. One statement; same validation as run_query. parameters — Named parameters for driver placeholders (e.g. %(name)s or {name:Type}). database — Session default database for unqualified names. Src: databases. profile — Profile name; uses default profile when omitted. Src: profiles. types — EXPLAIN variants: plan (indexes), pipeline, syntax. Default plan and pipeline if omitted.
list_databases	List databases. Rows from system.databases visible to the connection.	profile — Profile name; uses default profile when omitted. Src: profiles.
list_tables	List tables and views in a database. Rows from system.tables: name, engine, primary_key, sorting_key, partition_key, total_rows, total_bytes for query planning.	database — Database to list; client default when omitted. Src: databases. profile — Profile name; uses default profile when omitted. Src: profiles.
list_columns	List columns for a table or view. Rows from system.columns for the resolved database and table.	table (required) — Table or view name, or database.table. Src: tables. database — Database when table is unqualified; ignored if table contains a dot. Client default when omitted. Src: databases. profile — Profile name; uses default profile when omitted. Src: profiles.

Resources

The server exposes the same discovery and metadata as the tools above via URI-addressable resources (profile-first hierarchy). Each resource’s description matches the corresponding tool (list_profiles, get_cluster_properties, list_databases, list_tables, list_columns), plus Src: tags for URI path parameters. All resource content is JSON (application/json) except snapshots which return CSV (text/csv). Use path segment default for the default profile or database.

Resource descriptions match description=… on @mcp.resource in server.py (same prefix omission as above).

URI	Description
chx://profiles	List configured profiles. Each entry includes name and optional description.
chx://profiles/{profile}/cluster-properties	Get cluster properties and execution limits. Returns ClickHouse server version plus enforced limits (max rows, timeouts) for the profile. Src: profiles.
chx://profiles/{profile}/databases	List databases. Rows from system.databases visible to the connection. Src: profiles.
chx://profiles/{profile}/databases/{database}/tables	List tables and views in a database. Rows from system.tables: name, engine, primary_key, sorting_key, partition_key, total_rows, total_bytes for query planning. Src: profiles, dbs.
chx://profiles/{profile}/databases/{database}/tables/{table}/columns	List columns for a table or view. Rows from system.columns for the resolved database and table. Src: profiles, dbs, tables.
chx://snapshots/{id}	Fetch a query result snapshot by ID. Returns the full result as a CSV string (header row + data rows). Entries expire after 7 days. Src: run_query with snapshot=true.

Security

Read-only SQL only: run_query allows SELECT / WITH … SELECT; run_show allows a single SHOW statement per call. INTO OUTFILE is not allowed on run_show. Interactive queries enforce a tight row cap (default 500, hard ceiling 1 000); for larger extracts use snapshot=true (default 10 000, hard ceiling 50 000). Parameterized queries are supported where the driver allows (%(name)s or {name:Type} syntax). Use environment variables for connection credentials — never commit secrets.

MCP host examples

Snippets for common MCP clients using uvx mcp-clickhousex (no clone required; ensure uv is on your PATH). Replace connection details as needed.

Cursor

{
  "mcpServers": {
    "clickhouse": {
      "command": "uvx",
      "args": ["mcp-clickhousex"],
      "env": {
        "MCP_CLICKHOUSE_DSN": "http://default:@localhost:8123/default"
      }
    }
  }
}

Codex

[mcp_servers.clickhouse]
command = "uvx"
args = ["mcp-clickhousex"]

[mcp_servers.clickhouse.env]
MCP_CLICKHOUSE_DSN = "http://default:@localhost:8123/default"

OpenCode

{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "clickhouse": {
      "type": "local",
      "enabled": true,
      "command": ["uvx", "mcp-clickhousex"],
      "environment": {
        "MCP_CLICKHOUSE_DSN": "http://default:@localhost:8123/default"
      }
    }
  }
}

Claude Code

{
  "mcpServers": {
    "clickhouse": {
      "command": "uvx",
      "args": ["mcp-clickhousex"],
      "env": {
        "MCP_CLICKHOUSE_DSN": "http://default:@localhost:8123/default"
      }
    }
  }
}

Copilot

{
  "inputs": [],
  "servers": {
    "clickhouse": {
      "type": "stdio",
      "command": "uvx",
      "args": ["mcp-clickhousex"],
      "env": {
        "MCP_CLICKHOUSE_DSN": "http://default:@localhost:8123/default"
      }
    }
  }
}

Config file locations: Cursor .cursor/mcp.json, Codex/Copilot/OpenCode vary by client; see your client's MCP docs.

Tests

Tests require a running ClickHouse instance. The test suite creates a sample table in the default database, seeds it, and drops it after.

# Run all tests (unit + functional + e2e)
uv run pytest tests/ -v

The test harness uses MCP_TEST_CLICKHOUSE_DSN to locate the ClickHouse instance. If unset, it falls back to http://admin:password123@localhost:8123/default. Set the variable to point tests at a different server without affecting your production MCP_CLICKHOUSE_DSN:

export MCP_TEST_CLICKHOUSE_DSN="http://user:pass@testhost:8123/default"
uv run pytest tests/ -v

Roadmap

No planned features at this time. Open an issue to suggest improvements.

Contributing

Open issues or PRs; follow existing style and add tests where appropriate.

License

MIT. See LICENSE.