db-mcp (PostgreSQL)

MCP server in JavaScript: PostgreSQL over stdio, read-only tools (SELECT / WITH) plus schema helpers.

Repo layout

Root package.json deps: @modelcontextprotocol/sdk, pg, zod, dotenv.

Related MCP server: PostgreSQL MCP Server

Requirements

• Node.js 18+

• PostgreSQL and a DATABASE_URL

Install (MCP server)

cd db-mcp
npm install

Copy .env.example → .env in repo root (next to root package.json). Set DATABASE_URL. Do not commit .env.

src/index.js loads that .env via dotenv using path repo root (derived from import.meta.url), so Cursor can run node …/src/index.js with any cwd. Vars already in the real environment are not overwritten.

Alternatively: export DATABASE_URL in the shell, or set env in Cursor MCP config (those win over .env).

Configuration (MCP)

Connection startup uses libpq -c default_transaction_read_only=on and -c statement_timeout=… (see src/pool.js). Prefer a read-only DB role in production.

Run MCP (stdio)

npm start

PowerShell (if not using .env):

$env:DATABASE_URL = "postgresql://USER:PASSWORD@HOST:5432/DBNAME"
npm start

Cursor / Claude Desktop

Point command + args at src/index.js. Pass DATABASE_URL in env if you do not rely on root .env.

Cursor (mcp.json):

{
  "mcpServers": {
    "postgres": {
      "command": "node",
      "args": ["C:/Users/YourUser/Desktop/db-mcp/src/index.js"],
      "env": {
        "DATABASE_URL": "postgresql://USER:PASSWORD@localhost:5432/mydb"
      }
    }
  }
}

Use a real absolute path. Reload MCP after edits.

How to test

If tools never show: MCP disconnected in UI, or chat mode has no tool use.

Tools

pg_query: no multi-statement (; only at end); must start with SELECT or WITH.

Security

• DATABASE_URL = secret; least-privilege role.

• Read-only intent; DB should still enforce if default_transaction_read_only bypassed.

• LLM + SQL = cost + data exposure risk; tight timeouts, read replica when possible.

• Playground = local dev only; do not expose API without auth.

License

MIT