Multi Database MCP Server

A powerful multi-database server implementing the Model Context Protocol (MCP) to provide AI assistants with structured access to databases.

Overview

The DB MCP Server provides a standardized way for AI models to interact with multiple databases simultaneously. Built on the FreePeak/cortex framework, it enables AI assistants to execute SQL queries, manage transactions, explore schemas, and analyze performance across different database systems through a unified interface.

Core Concepts

Multi-Database Support

Unlike traditional database connectors, DB MCP Server can connect to and interact with multiple databases concurrently:

{
  "connections": [
    {
      "id": "mysql1",
      "type": "mysql",
      "host": "localhost",
      "port": 3306,
      "name": "db1",
      "user": "user1",
      "password": "password1"
    },
    {
      "id": "postgres1",
      "type": "postgres",
      "host": "localhost",
      "port": 5432,
      "name": "db2",
      "user": "user2",
      "password": "password2"
    },
    {
      "id": "oracle1",
      "type": "oracle",
      "host": "localhost",
      "port": 1521,
      "service_name": "XEPDB1",
      "user": "user3",
      "password": "password3"
    }
  ]
}

Dynamic Tool Generation

For each connected database, the server automatically generates specialized tools:

// For a database with ID "mysql1", these tools are generated:
query_mysql1       // Execute SQL queries
execute_mysql1     // Run data modification statements
transaction_mysql1 // Manage transactions
schema_mysql1      // Explore database schema
performance_mysql1 // Analyze query performance

Clean Architecture

The server follows Clean Architecture principles with these layers:

1. Domain Layer: Core business entities and interfaces
2. Repository Layer: Data access implementations
3. Use Case Layer: Application business logic
4. Delivery Layer: External interfaces (MCP tools)

Features

• Simultaneous Multi-Database Support: Connect to multiple MySQL, PostgreSQL, SQLite, and Oracle databases concurrently
• Lazy Loading Mode: Defer connection establishment until first use - perfect for setups with 10+ databases (enable with --lazy-loading flag)
• Database-Specific Tool Generation: Auto-creates specialized tools for each connected database
• Clean Architecture: Modular design with clear separation of concerns
• OpenAI Agents SDK Compatibility: Full compatibility for seamless AI assistant integration
• Dynamic Database Tools: Execute queries, run statements, manage transactions, explore schemas, analyze performance
• Unified Interface: Consistent interaction patterns across different database types
• Connection Management: Simple configuration for multiple database connections
• Health Check: Automatic validation of database connectivity on startup
• Production Guardrails: Per-database read_only enforcement (blocks writes through both query_* and execute_* tools), max_rows result truncation with explicit notices, and per-query timeouts

Production Guardrails

Protect agent sessions against runaway queries and accidental writes:

| DB_MCP_AUDIT_LOG=/path/audit.jsonl | process | Appends one JSONL record per executed statement — timestamp, op (query/execute/tx_*), database, statement (capped at 10k chars), duration, error. Includes rejected attempts against read-only databases. Best-effort writes never fail a query; file is created with 0600. |

Defense in depth: read-only is enforced in three layers — application classifier, engine session defaults, and (recommended) least-privilege database users. Oracle currently relies on the classifier plus user privileges.

Supported Databases

Deployment Options

The DB MCP Server can be deployed in multiple ways to suit different environments and integration needs:

Docker Deployment

# Pull the latest image
docker pull freepeak/db-mcp-server:latest

# Run with mounted config file
docker run -p 9092:9092 \
  -v $(pwd)/config.json:/app/my-config.json \
  -e TRANSPORT_MODE=sse \
  -e CONFIG_PATH=/app/my-config.json \
  -e DB_MCP_API_KEY=replace-me-with-a-long-random-string \
  freepeak/db-mcp-server

Note: Mount to /app/my-config.json as the container has a default file at /app/config.json.

API-Key Authentication

The SSE and streamable-HTTP transports accept an Authorization: Bearer <key> header. Set DB_MCP_API_KEY (or pass -api-key) when launching the Docker container; clients must then send the matching bearer token on every request:

curl -H "Authorization: Bearer replace-me-with-a-long-random-string" \
     http://localhost:9092/sse

When no API key is configured the transport remains open (single-user / development use). The middleware lives in internal/delivery/mcp.APIKeyAuth and is exported so you can compose it with your own reverse proxy if you front the container with nginx, Caddy, or Traefik.

STDIO Mode (IDE Integration)

# Run the server in STDIO mode
./bin/server -t stdio -c config.json

For Cursor IDE integration, add to .cursor/mcp.json:

{
  "mcpServers": {
    "stdio-db-mcp-server": {
      "command": "/path/to/db-mcp-server/server",
      "args": ["-t", "stdio", "-c", "/path/to/config.json"]
    }
  }
}

SSE Mode (Server-Sent Events)

# Default configuration (localhost:9092)
./bin/server -t sse -c config.json

# Custom host and port
./bin/server -t sse -host 0.0.0.0 -port 8080 -c config.json

Client connection endpoint: http://localhost:9092/sse

Source Code Installation

# Clone the repository
git clone https://github.com/FreePeak/db-mcp-server.git
cd db-mcp-server

# Build the server
make build

# Run the server
./bin/server -t sse -c config.json

Configuration

Database Configuration File

Create a config.json file with your database connections:

{
  "connections": [
    {
      "id": "mysql1",
      "type": "mysql",
      "host": "mysql1",
      "port": 3306,
      "name": "db1",
      "user": "user1",
      "password": "password1",
      "query_timeout": 60,
      "max_open_conns": 20,
      "max_idle_conns": 5,
      "conn_max_lifetime_seconds": 300,
      "conn_max_idle_time_seconds": 60,
      "read_only": false,
      "max_rows": 1000,
      "masking_rules": [
        { "pattern": "(?i)email", "strategy": "fixed_string", "value": "***MASKED***" },
        { "pattern": "(?i)(ssn|tax_id)", "strategy": "null" }
      ]
    },
    {
      "id": "postgres1",
      "type": "postgres",
      "host": "postgres1",
      "port": 5432,
      "name": "db1",
      "user": "user1",
      "password": "password1"
    },
    {
      "id": "sqlite_app",
      "type": "sqlite",
      "database_path": "./data/app.db",
      "journal_mode": "WAL",
      "cache_size": 2000,
      "read_only": false,
      "use_modernc_driver": true,
      "query_timeout": 30,
      "max_open_conns": 1,
      "max_idle_conns": 1
    },
    {
      "id": "sqlite_encrypted",
      "type": "sqlite",
      "database_path": "./data/secure.db",
      "encryption_key": "your-secret-key-here",
      "journal_mode": "WAL",
      "use_modernc_driver": false
    },
    {
      "id": "sqlite_memory",
      "type": "sqlite",
      "database_path": ":memory:",
      "cache_size": 1000,
      "use_modernc_driver": true
    }
  ]
}

Command-Line Options

# Basic syntax
./bin/server -t <transport> -c <config-file>

# SSE transport options
./bin/server -t sse -host <hostname> -port <port> -c <config-file>

# Lazy loading mode (recommended for 10+ databases)
./bin/server -t stdio -c <config-file> --lazy-loading

# Customize log directory (useful for multi-project setups)
./bin/server -t stdio -c <config-file> -log-dir /tmp/db-mcp-logs

# Inline database configuration
./bin/server -t stdio -db-config '{"connections":[...]}'

# Environment variable configuration
export DB_CONFIG='{"connections":[...]}'
./bin/server -t stdio

Available Flags:

• -t, -transport: Transport mode (stdio or sse)
• -c, -config: Path to database configuration file
• -p, -port: Server port for SSE mode (default: 9092)
• -h, -host: Server host for SSE mode (default: localhost)
• -log-level: Log level (debug, info, warn, error)
• -log-dir: Directory for log files (default: ./logs in current directory)
• -db-config: Inline JSON database configuration

Environment Variables

Values in a .env file are loaded first; real environment variables take precedence. A JSON config file (CONFIG_PATH/DB_CONFIG_FILE) overrides per-database env vars.

SQLite Configuration Options

When using SQLite databases, you can leverage these additional configuration options:

SQLite Connection Parameters

SQLite Examples

Basic File Database

{
  "id": "my_sqlite_db",
  "type": "sqlite",
  "database_path": "./data/myapp.db",
  "journal_mode": "WAL",
  "cache_size": 2000
}

Encrypted Database (SQLCipher)

{
  "id": "encrypted_db",
  "type": "sqlite",
  "database_path": "./data/secure.db",
  "encryption_key": "your-secret-encryption-key",
  "use_modernc_driver": false
}

In-Memory Database

{
  "id": "memory_db",
  "type": "sqlite",
  "database_path": ":memory:",
  "cache_size": 1000
}

Read-Only Database

{
  "id": "reference_data",
  "type": "sqlite",
  "database_path": "./data/reference.db",
  "read_only": true,
  "journal_mode": "DELETE"
}

Oracle Configuration Options

When using Oracle databases, you can leverage these additional configuration options:

Oracle Connection Parameters

Oracle Examples

Basic Oracle Connection (Development)

{
  "id": "oracle_dev",
  "type": "oracle",
  "host": "localhost",
  "port": 1521,
  "service_name": "XEPDB1",
  "user": "testuser",
  "password": "testpass",
  "max_open_conns": 50,
  "max_idle_conns": 10,
  "conn_max_lifetime_seconds": 1800
}

Oracle with SID (Legacy)

{
  "id": "oracle_legacy",
  "type": "oracle",
  "host": "oracledb.company.com",
  "port": 1521,
  "sid": "ORCL",
  "user": "app_user",
  "password": "app_password"
}

Oracle Cloud Autonomous Database (with Wallet)

{
  "id": "oracle_cloud",
  "type": "oracle",
  "user": "ADMIN",
  "password": "your-cloud-password",
  "wallet_location": "/path/to/wallet_DBNAME",
  "service_name": "dbname_high"
}

Oracle RAC (Real Application Clusters)

{
  "id": "oracle_rac",
  "type": "oracle",
  "host": "scan.company.com",
  "port": 1521,
  "service_name": "production",
  "user": "app_user",
  "password": "app_password",
  "max_open_conns": 100,
  "max_idle_conns": 20
}

Oracle with TNS Entry

{
  "id": "oracle_tns",
  "type": "oracle",
  "tns_admin": "/opt/oracle/network/admin",
  "tns_entry": "PROD_DB",
  "user": "app_user",
  "password": "app_password"
}

Oracle with Edition-Based Redefinition

{
  "id": "oracle_ebr",
  "type": "oracle",
  "host": "oracledb.company.com",
  "port": 1521,
  "service_name": "production",
  "user": "app_user",
  "password": "app_password",
  "edition": "v2_0"
}

Oracle Connection String Priority

When multiple connection methods are configured, the following priority is used:

1. TNS Entry (if tns_entry and tns_admin are configured)
2. Wallet (if wallet_location is configured) - for Oracle Cloud
3. Standard (host:port/service_name) - default method

Available Tools

For each connected database, DB MCP Server automatically generates these specialized tools:

Query Tools

Schema Tools

Performance Tools

TimescaleDB Tools

For PostgreSQL databases with the timescaledb extension installed, these additional specialized tools are registered automatically at startup (registration is config-driven, so it also works under --lazy-loading; each handler verifies the extension at call time and returns an actionable error when it is absent):

In unified mode the same seven tools appear once as timescaledb_timeseries_query, timescaledb_analyze_timeseries, timescaledb_list_hypertables, timescaledb_compression_settings, timescaledb_retention_policy, timescaledb_list_continuous_aggregates, and timescaledb_continuous_aggregate_info, each taking a required database parameter.

Scope note: read-only discovery above goes through the query pipeline and therefore stays usable on read_only databases; each handler checks for the timescaledb extension first. Write-policy operations (hypertable creation, compression toggles, add/remove retention or refresh policies) remain unexposed — use plain SQL through the query/execute tools in the meantime. For detailed documentation, see TIMESCALEDB_TOOLS.md.

Unified Tool Mode

If you connect many databases (5+), the per-database tool naming generates a large number of tools (5 × N). Some MCP clients — Claude in particular — apply strict limits on the total number of tools and tool description size that can cause the agent to fail to load the server, ignore tools, or refuse to call them. Issue #18 documents this exact symptom: "the db-mcp-server does not function properly with Claude, even though it works fine with OpenAI".

For these clients, launch the server with the --unified-tools flag to register six consolidated tools (query, execute, transaction, performance, explain, describe, schema, filter_tables) instead of per-database tools:

./bin/server -t stdio -c config.json --unified-tools

Context-window cost (measured, TestToolTokenBenchmark, re-verified 2026-08 via scripts/token-benchmark.sh): unified mode costs ~1.25–1.6k tokens regardless of how many databases are connected, while per-database mode costs ~800 tokens per database (7 tools each) — 10 connected databases ≈ 8k tokens, an 80% wire-payload saving with unified. With one database only, per-database naming is slightly cheaper; unified wins from two databases onward and scales flat thereafter. Re-measure the real wire payload yourself with scripts/token-benchmark.sh; methodology and results in docs/benchmark-token-efficiency.md.

In unified mode, each tool accepts a required `database` parameter that names
which database the call should target. See the [Configuration](#configuration)
section for the full list of available databases. This dramatically reduces the
tool count and the cumulative description size, which resolves the Claude
compatibility issues.

For very large configurations, also enable `--lazy-loading` so that startup
doesn't open connections to databases that may never be queried during the
session.

## Examples

### Querying Multiple Databases

```sql
-- Query the MySQL database
query_mysql1("SELECT * FROM users LIMIT 10")

-- Query the PostgreSQL database in the same context
query_postgres1("SELECT * FROM products WHERE price > 100")

-- Query the SQLite database
query_sqlite_app("SELECT * FROM local_data WHERE created_at > datetime('now', '-1 day')")

-- Query the Oracle database
query_oracle_dev("SELECT * FROM employees WHERE hire_date > SYSDATE - 30")

Managing Transactions

The transaction_<db_id> tool supports begin, execute, commit, and rollback actions. Each begin returns a transactionId; pass it back to stage statements and to commit or roll back:

// 1. Start a transaction
{ "action": "begin" }
// → { "transactionId": "tx_mysql1_1730000000000000000" }

// 2. Execute statements within the transaction
{
  "action": "execute",
  "transactionId": "tx_mysql1_1730000000000000000",
  "statement": "INSERT INTO orders (customer_id, product_id) VALUES (1, 2)"
}

// 3a. Commit — persists all staged statements
{ "action": "commit", "transactionId": "tx_mysql1_1730000000000000000" }

// 3b. OR rollback — discards all staged statements
{ "action": "rollback", "transactionId": "tx_mysql1_1730000000000000000" }

Unknown or already-retired transaction IDs return a clear error instead of a silent success, so agents can detect and recover from lost-transaction situations.

Exploring Database Schema

-- Get all tables in the database
schema_mysql1("tables")

-- Get columns for a specific table
schema_mysql1("columns", "users")

-- Get constraints
schema_mysql1("constraints", "orders")

Working with SQLite-Specific Features

-- Create a table in SQLite
execute_sqlite_app("CREATE TABLE IF NOT EXISTS local_cache (key TEXT PRIMARY KEY, value TEXT, timestamp DATETIME)")

-- Use SQLite-specific date functions
query_sqlite_app("SELECT * FROM events WHERE date(created_at) = date('now')")

-- Query SQLite master table for schema information
query_sqlite_app("SELECT name, sql FROM sqlite_master WHERE type='table' AND name NOT LIKE 'sqlite_%'")

-- Performance optimization with WAL mode
execute_sqlite_app("PRAGMA journal_mode = WAL")
execute_sqlite_app("PRAGMA synchronous = NORMAL")

Working with Oracle-Specific Features

-- Query user tables (excludes system schemas)
query_oracle_dev("SELECT table_name FROM user_tables ORDER BY table_name")

-- Use Oracle-specific date functions
query_oracle_dev("SELECT employee_id, hire_date FROM employees WHERE hire_date >= TRUNC(SYSDATE, 'YEAR')")

-- Oracle sequence operations
execute_oracle_dev("CREATE SEQUENCE emp_seq START WITH 1000 INCREMENT BY 1")
query_oracle_dev("SELECT emp_seq.NEXTVAL FROM DUAL")

-- Oracle-specific data types
query_oracle_dev("SELECT order_id, TO_CHAR(order_date, 'YYYY-MM-DD HH24:MI:SS') FROM orders")

-- Get schema metadata from Oracle data dictionary
query_oracle_dev("SELECT column_name, data_type, nullable FROM user_tab_columns WHERE table_name = 'EMPLOYEES'")

-- Use Oracle analytic functions
query_oracle_dev("SELECT employee_id, salary, RANK() OVER (ORDER BY salary DESC) as salary_rank FROM employees")

Troubleshooting

Common Issues

• Connection Failures: Verify network connectivity and database credentials
• Permission Errors: Ensure the database user has appropriate permissions
• Timeout Issues: Check the query_timeout setting in your configuration

Logs

Enable verbose logging for troubleshooting:

./bin/server -t sse -c config.json -v

Testing

Running Tests

The project includes comprehensive unit and integration tests for all supported databases.

Unit Tests

Run unit tests (no database required):

make test
# or
go test -short ./...

Integration Tests

Integration tests require running database instances. We provide Docker Compose configurations for easy setup.

Test All Databases:

# Start test databases
docker-compose -f docker-compose.test.yml up -d

# Run all integration tests
go test ./... -v

# Stop test databases
docker-compose -f docker-compose.test.yml down -v

Test Oracle Database:

# Start Oracle test environment
./oracle-test.sh start

# Run Oracle tests
./oracle-test.sh test
# or manually
ORACLE_TEST_HOST=localhost go test -v ./pkg/db -run TestOracle
ORACLE_TEST_HOST=localhost go test -v ./pkg/dbtools -run TestOracle

# Stop Oracle test environment
./oracle-test.sh stop

# Full cleanup (removes volumes)
./oracle-test.sh cleanup

Test TimescaleDB:

# Start TimescaleDB test environment
./timescaledb-test.sh start

# Run TimescaleDB tests
TIMESCALEDB_TEST_HOST=localhost go test -v ./pkg/db/timescale ./internal/delivery/mcp

# Stop TimescaleDB test environment
./timescaledb-test.sh stop

Regression Tests

Run comprehensive regression tests across all database types:

# Ensure all test databases are running
docker-compose -f docker-compose.test.yml up -d
./oracle-test.sh start

# Run regression tests
MYSQL_TEST_HOST=localhost \
POSTGRES_TEST_HOST=localhost \
ORACLE_TEST_HOST=localhost \
go test -v ./pkg/db -run TestRegression

# Run connection pooling tests
go test -v ./pkg/db -run TestConnectionPooling

Continuous Integration

All tests run automatically on every pull request via GitHub Actions. The CI pipeline includes:

• Unit Tests: Fast tests that don't require database connections
• Integration Tests: Tests against MySQL, PostgreSQL, SQLite, and Oracle databases
• Regression Tests: Comprehensive tests ensuring backward compatibility
• Linting: Code quality checks with golangci-lint

Contributing

We welcome contributions to the DB MCP Server project! To contribute:

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'feat: add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

Please see our CONTRIBUTING.md file for detailed guidelines.

Testing Your Changes

Before submitting a pull request, please ensure:

1. All unit tests pass: go test -short ./...
2. Integration tests pass for affected databases
3. Code follows the project's style guidelines: golangci-lint run ./...
4. New features include appropriate test coverage

License

This project is licensed under the MIT License - see the LICENSE file for details.