BigQuery MCP Server

A Model Context Protocol (MCP) server that enables LLMs to interact with Google BigQuery. Built with FastMCP (Python) and designed for ephemeral cloud environments where only environment variables are available (no file-based credentials).

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Features

Tool	Description
bq_list_datasets	List all datasets in the configured project
bq_list_tables	List tables in a dataset with row counts and size in MB
bq_get_schema	Get the full schema of a table (columns, types, descriptions)
bq_dry_run	Validate SQL and estimate query cost (~$6.25/TB)
bq_run_query	Execute SQL and return results (auto-appends LIMIT 1000 if missing)

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Project Structure

bigquery-mcp-server/
├── src/
│   ├── server.py                 # Entry point — starts the MCP server
│   ├── constants.py              # Global constants (BigQuery config, limits)
│   ├── tools/
│   │   └── bigquery.py           # All 5 BigQuery tools
│   └── services/
│       ├── bigquery_client.py    # BigQuery client factory + row serialization
│       └── error_handler.py      # Centralized BigQuery error handling
├── main.py                       # Root-level entry point wrapper
├── Dockerfile                    # Multi-stage Docker build
├── docker-compose.yml            # Server + MCP Inspector
├── docker-compose.dev.yml        # Dev mode with hot-reload
├── mcp.json                      # MCP client configuration
├── pyproject.toml                # Project metadata and dependencies
└── requirements.txt              # Pip-compatible dependencies

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Environment Variables

Variable	Required	Default	Description
BIGQUERY_PROJECT_ID	Yes	—	GCP project ID (e.g. my-project-123)
BIGQUERY_SERVICE_ACCOUNT_JSON_CONTENT	Yes	—	Raw JSON string of the service account key
BIGQUERY_LOCATION	No	US	BigQuery dataset region
TRANSPORT	No	stdio	Transport mode: stdio or http
PORT	No	8000	HTTP server port
HOST	No	127.0.0.1	HTTP server bind address

Authentication

This server authenticates using a service account JSON provided directly via environment variable — no file paths, no gcloud CLI.

1. Create a service account in the GCP Console with at least:
   • BigQuery Data Viewer (roles/bigquery.dataViewer)
   • BigQuery Job User (roles/bigquery.jobUser)
2. Generate a JSON key for the service account
3. Set the full JSON string as BIGQUERY_SERVICE_ACCOUNT_JSON_CONTENT

export BIGQUERY_PROJECT_ID="my-project-123"
export BIGQUERY_SERVICE_ACCOUNT_JSON_CONTENT='{"type":"service_account","project_id":"...","private_key":"...","client_email":"...","...":"..."}'

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Quick Start

Option A — uvx (Recommended)

No manual install needed. uvx downloads the package from PyPI, creates an isolated environment, and runs the server:

uvx bigquery-mcp-server

For MCP clients (Claude Code, Cursor, etc.), configure the server in your client's MCP config:

{
  "mcpServers": {
    "bigquery-mcp": {
      "command": "uvx",
      "args": ["bigquery-mcp-server"],
      "env": {
        "BIGQUERY_PROJECT_ID": "my-project-123",
        "BIGQUERY_SERVICE_ACCOUNT_JSON_CONTENT": "{ ... }"
      }
    }
  }
}

Note: Env vars must be passed explicitly via the env block in your MCP client config.

Option B — Local (virtualenv)

# Create virtual environment and install
python -m venv .venv
source .venv/bin/activate      # Windows: .venv\Scripts\activate
pip install -e .

# Set credentials (or use a .env file)
export BIGQUERY_PROJECT_ID="my-project-123"
export BIGQUERY_SERVICE_ACCOUNT_JSON_CONTENT='{ ... }'

# Run in stdio mode
python main.py

# Or HTTP mode (for MCP Inspector)
TRANSPORT=http python main.py

Option C — Docker

# Set env vars in a .env file or export them, then:
docker compose up --build

# Open MCP Inspector at http://localhost:6274
# Connect to: http://mcp-server:8000/mcp (Streamable HTTP)

Option D — Dev mode with hot-reload

docker compose -f docker-compose.dev.yml up --build

# In another terminal:
npx @modelcontextprotocol/inspector
# Connect to: http://localhost:8000/mcp (Streamable HTTP)

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Testing with MCP Inspector CLI

# List all tools
npx @modelcontextprotocol/inspector --cli \
  --config mcp.json --server bigquery-mcp \
  --method tools/list

# List datasets
npx @modelcontextprotocol/inspector --cli \
  --config mcp.json --server bigquery-mcp \
  --method tools/call --tool-name bq_list_datasets

# List tables in a dataset
npx @modelcontextprotocol/inspector --cli \
  --config mcp.json --server bigquery-mcp \
  --method tools/call --tool-name bq_list_tables \
  --tool-arg 'params={"dataset": "my_dataset"}'

# Get table schema
npx @modelcontextprotocol/inspector --cli \
  --config mcp.json --server bigquery-mcp \
  --method tools/call --tool-name bq_get_schema \
  --tool-arg 'params={"dataset": "my_dataset", "table": "my_table"}'

# Dry run a query
npx @modelcontextprotocol/inspector --cli \
  --config mcp.json --server bigquery-mcp \
  --method tools/call --tool-name bq_dry_run \
  --tool-arg 'params={"sql": "SELECT * FROM my_dataset.my_table"}'

# Run a query
npx @modelcontextprotocol/inspector --cli \
  --config mcp.json --server bigquery-mcp \
  --method tools/call --tool-name bq_run_query \
  --tool-arg 'params={"sql": "SELECT * FROM my_dataset.my_table LIMIT 10"}'

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Connect to Claude Code

Using uvx (recommended):

claude mcp add bigquery-mcp uvx -- bigquery-mcp-server

Or add to ~/.claude/mcp.json:

{
  "mcpServers": {
    "bigquery-mcp": {
      "command": "uvx",
      "args": ["bigquery-mcp-server"],
      "env": {
        "BIGQUERY_PROJECT_ID": "my-project-123",
        "BIGQUERY_SERVICE_ACCOUNT_JSON_CONTENT": "{ ... }"
      }
    }
  }
}

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Transports

Transport	How to activate	When to use
stdio	TRANSPORT=stdio python -m src.server	Claude Code, Cursor, local integration
HTTP	TRANSPORT=http python -m src.server	MCP Inspector, remote servers

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Safety Features

• Auto LIMIT: bq_run_query automatically appends LIMIT 1000 if no LIMIT clause is detected, preventing accidental large data transfers
• Dry run: bq_dry_run validates SQL and estimates cost before execution
• Input validation: All tool inputs validated with Pydantic v2
• Error handling: BigQuery exceptions (403, 404, 400, etc.) are caught and returned as human-readable strings — the server never crashes
• Type serialization: Dates, datetimes, decimals, and bytes are automatically converted to JSON-safe types

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References

• FastMCP Docs
• MCP Python SDK
• MCP Inspector
• MCP Protocol Docs
• BigQuery Python Client