db-conn-mcp 0.2.0

A dead-simple, self-hosted MCP server for securely querying databases via AI agents.

db-conn-mcp

A dead-simple, self-hosted Model Context Protocol (MCP) server for querying your databases with AI agents (Claude, Cursor, Windsurf, VS Code, Zed, and more).

It does one thing well: let an agent safely explore and query a database you point it at — with security delegated to the simplest possible primitives (a static JSON file and your database's own read-only transactions), not custom auth servers or fragile SQL parsing.

v1 ships PostgreSQL only. All database-specific code lives behind a Dialect seam, so adding MySQL/SQLite later is a single new file.

---

Why

• Read stays read. A read database runs every query in a native read-only transaction, and the read tool only accepts a single read-only statement (SELECT/WITH/VALUES/TABLE/SHOW/EXPLAIN) — so an agent can't slip in a write or a SET … READ WRITE to flip the session. For a hard, privilege-level guarantee that holds no matter what, point the DSN at a read-only database role (see Use a read-only role).
• No secret leaks. DSNs/passwords are never logged or returned by any tool. Connection failures come back as sanitized diagnostics (a category + fix), never a raw traceback with your host and credentials in it.
• Tiered write safety. Writes are gated server-side: mode (hard, native) → yolo (per-database trust) → user_consent (explicit per-operation approval).
• Zero-friction setup. An interactive wizard registers your database and injects the server into your AI client's config for you — across 8 popular clients, each in its own format.

---

Install

Requires Python 3.10+.

# Recommended: isolated but globally available on your PATH
pipx install db-conn-mcp

# or plain pip
pip install db-conn-mcp

This installs the db-conn-mcp command.

---

Quick start

db-conn-mcp setup

The wizard asks for:

1. Scope — global (~/.db-conn-mcp/connections.json) or repo (./connections.json).
2. Connection name — e.g. prod.
3. DSN — e.g. postgresql://user:pass@host:5432/dbname.
4. Mode — read (recommended) or write.
5. Client injection — pick which detected MCP clients to wire up (e.g. 1,3 or all).

It then writes your config and (optionally) registers the server in your chosen AI clients. Restart/reconnect the client and the tools are available.

Cancelling is safe. Press Ctrl+C at any prompt and nothing is written.

---

Configuration

The single source of truth is connections.json, resolved in this order (first match wins):

1. --config /path/to/connections.json
2. ./connections.json (repo-scoped)
3. ~/.db-conn-mcp/connections.json (global-scoped)

{
  "connections": [
    { "name": "prod", "dsn": "postgresql://…", "mode": "read" },
    { "name": "dev",  "dsn": "postgresql://…", "mode": "write", "yolo": false }
  ]
}

Field	Required	Meaning
name	yes	Unique identifier the agent uses to pick a database.
dsn	yes	Connection string. Secret — never shown by any tool.
mode	yes	read or write. An absolute, native security boundary.
yolo	no (default false)	If true, skip the per-write consent prompt for this database.

connections.json is git-ignored by this project's .gitignore — never commit real DSNs.

---

The security model

Writes pass through three gates, in order:

1. mode (hard, native). If the database isn't "mode": "write", the write is rejected — and the connection is opened read-only at the PostgreSQL session level regardless, so it's blocked twice over. yolo and user_consent can never make a read database writable.
2. yolo (persisted trust). On a write database with yolo: true, writes proceed without prompting.
3. user_consent (per-operation). Otherwise the agent must first read the schema, show you the exact SQL, get your "yes", and re-call with user_consent=true.

Reads always run inside a native read-only transaction, and execute_read_query accepts only a single read-only statement (SELECT/WITH/VALUES/TABLE/SHOW/EXPLAIN). That allowlist is what stops an agent from sending SET SESSION CHARACTERISTICS AS TRANSACTION READ WRITE to flip the session, or piggy-backing a ; DELETE … onto a read — there's no SQL parsing involved, just a leading-keyword check plus the driver's single-command protocol.

Use a read-only role (strongest guarantee)

The application-level checks above are defense-in-depth. The hardest boundary is a privilege one: connect with a PostgreSQL role that simply cannot write, so a write fails even if every layer above were bypassed. Create one per database and use its DSN for read connections:

CREATE ROLE agent_ro LOGIN PASSWORD '…';
GRANT CONNECT ON DATABASE mydb TO agent_ro;
GRANT USAGE ON SCHEMA public TO agent_ro;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO agent_ro;
ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO agent_ro;

This is the recommended setup for any database that holds data you care about.

---

MCP tools

The server exposes 10 tools and 1 prompt:

Tool	Kind	Description
list_databases	explore	Configured databases (name, mode, yolo — no DSN).
list_tables	explore	Tables and views in a database.
get_table_schema	explore	Columns, types, primary/foreign keys for a table.
sample_table_rows	explore	First N rows of a table (default 10).
find_columns	search	Find columns by name across all tables (fuzzy, case-insensitive).
search_value	search	Find where a value appears across tables (fuzzy); returns table/column hits + samples. Pass tables=[…] to scope it.
execute_read_query	execute	Run a single read-only statement (SELECT/WITH/…) inside a read-only transaction.
execute_write_query	execute	Run a mutation — gated by the safety model above.
set_yolo_mode	config	Enable/disable yolo for one database (persisted).
check_database	doctor	Test one database (or all) → OK or a sanitized diagnostic.

Prompt: troubleshoot_connection — a discoverable, full connection-gotchas checklist (host/port, firewall, sslmode, Docker localhost, db-name case, pool limits, …).

---

CLI reference

db-conn-mcp is both the server and a management tool.

Command	What it does
db-conn-mcp	Run the server over stdio (the default an MCP client uses).
db-conn-mcp --transport http	Run over HTTP (SSE) instead.
db-conn-mcp setup	Guided setup; shows status + an action menu if already configured.
db-conn-mcp status	List configured databases and which clients have the server injected.
db-conn-mcp add	Add another database connection.
db-conn-mcp clients	Inject the server into detected MCP clients.
db-conn-mcp clients --remove	Uninject the server from chosen clients.
db-conn-mcp check [name]	Probe connectivity (exit 0 all-OK, 2 if any unreachable).
db-conn-mcp remove <name>	Remove a connection.
db-conn-mcp yolo <name> on|off	Toggle yolo for one database.

--config <path> works before or after any subcommand.

---

Connecting an AI client

db-conn-mcp setup (or db-conn-mcp clients) auto-detects and writes the right config for:

Claude Desktop · Cursor · Windsurf · Agy (Antigravity) · Claude Code · Cline · VS Code · Zed

Prefer to wire it manually? Use the absolute path the wizard would (so the client can find it regardless of PATH). For a mcpServers-style client (Claude Desktop, Cursor, Windsurf, …):

{
  "mcpServers": {
    "db-conn-mcp": {
      "command": "db-conn-mcp",
      "args": ["--config", "/absolute/path/to/connections.json"]
    }
  }
}

If db-conn-mcp isn't on the client's PATH (e.g. a project-venv install), use the interpreter form instead: "command": "/abs/path/to/python", "args": ["-m", "db_conn_mcp", "--config", "…"]. The setup/clients commands figure this out for you automatically.

VS Code (servers key, "type": "stdio") and Zed (context_servers, nested command) use different shapes — the wizard handles those too.

---

Provider notes

• Railway / managed Postgres over a public proxy: use the public connection URL (e.g. Railway's DATABASE_PUBLIC_URL, not the internal *.railway.internal one) and append ?sslmode=require — these proxies require SSL with a self-signed cert, which sslmode=require accepts without verification.

---

Development

git clone https://github.com/Idle-Sync/db-conn-mcp
cd db-conn-mcp
python -m venv .venv && source .venv/bin/activate   # Windows: .venv\Scripts\Activate.ps1
pip install -e ".[dev]"

ruff check . && ruff format --check .
pytest -q

pyproject.toml is the single source of dependency truth. The codebase is split into single-purpose layers (config, models, dialects/, safety, diagnostics, handlers, server, cli); only the dialect layer knows a specific database exists. See ARCHITECTURE.md, PRD.md, and PLAN.md.

---

License

MIT — see LICENSE.