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) → dry-run first (a commit is refused unless that exact statement was previewed) → 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+.
pipx install db-conn-mcp
pip install db-conn-mcp
This installs the db-conn-mcp command.
Upgrade
Not sure how you installed it? Each manager keeps its own registry — ask them:
pipx list
uv tool list
pip show db-conn-mcp
If none of those know it, your MCP client config is likely launching it via uvx (check the command in the client's config entry — that entry is the source of truth for what actually runs, and which db-conn-mcp / Get-Command db-conn-mcp shows the binary on your PATH).
Then use the matching upgrade command:
pipx upgrade db-conn-mcp
pip install --upgrade db-conn-mcp
uv tool upgrade db-conn-mcp
Running via uvx (e.g. in an MCP client config)? There's nothing installed to upgrade, but uvx caches resolved versions — use db-conn-mcp@latest as the command to always resolve the newest release, or run uv cache clean db-conn-mcp to force a re-resolve.
After upgrading, restart/reconnect your AI client so it picks up the new version (and any new tools). Verify with db-conn-mcp -v.
PyPI's index can lag a release by a minute or two. If your upgrade reports "already at latest" right after a release, retry with pipx upgrade db-conn-mcp --pip-args="--no-cache-dir" (or pip install --upgrade --no-cache-dir db-conn-mcp).
Quick start
The wizard asks for:
- Scope — global (
~/.db-conn-mcp/connections.json) or repo (./connections.json).
- Connection name — e.g.
prod.
- DSN — e.g.
postgresql://user:pass@host:5432/dbname.
- Mode —
read (recommended) or write.
- Fallback ports (optional) — comma-separated extra ports to try if the primary one refuses; press Enter to skip.
- 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):
--config /path/to/connections.json./connections.json (repo-scoped)~/.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. The dry-run preview still applies. |
fallback_ports | no | Extra ports to probe, in order, when the primary port refuses or times out. See below. |
fallback_ports (optional) — extra ports probed in order when the
primary port refuses or times out (auth/TLS errors fail immediately and are never
masked). For DSNs behind SSH tunnels that don't always land on the same port.
The winning port is remembered for the server's lifetime and shown as
active_port in list_databases / check_database. Hand-edit the JSON (agents
may too) or answer the wizard prompt. Example:
"fallback_ports": [5433, 15432]
Probing is strictly opt-in and bounded: only the ports you list are ever tried (no
scanning), each fallback probe is capped at 5 seconds, and a connection without the key behaves
exactly as it always has. Existing connections.json files keep working untouched —
the server never adds the key to a file that doesn't have it.
connections.json is git-ignored by this project's .gitignore — never commit real DSNs.
The security model
Writes pass through four gates, in order:
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. Nothing — not yolo, not user_consent, not skip_dry_run — can ever make a read database writable.- Dry-run first (server-enforced).
execute_write_query defaults to dry_run=true. A commit is rejected unless the identical statement was dry-run first. The one escape hatch is skip_dry_run=true, which the agent passes to attest that you explicitly asked to skip the preview — the server can't verify that claim, so it's the same trust model as user_consent (and, like it, useless on a read database). yolo does not waive this stage.
yolo (persisted trust). On a write database with yolo: true, the previewed write commits without prompting.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.
What the dry-run does: it executes the statement in a transaction and always rolls back, returning the rows it would have affected — so only the mode gate applies, nothing commits, and you see the real impact before saying yes. The resulting permission to commit is scoped to that exact statement (same database, SQL, and params), expires after 10 minutes, and is consumed by the commit it authorizes — running the same statement twice means previewing it twice. (A dry-run does still execute server-side until rollback: brief locks, sequence advancement, trigger side effects.)
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.
The server exposes 23 tools and 2 prompts:
| Tool | Kind | Description |
|---|
list_databases | explore | Configured databases (name, mode, yolo, and active_port when a fallback port is in use — no DSN). |
list_tables | explore | Tables and views in a database. |
get_table_schema | explore | Columns, types, primary/foreign keys for a table. |
get_database_schema | explore | The whole database's schema in one deterministic call. format="json" (default) returns every table's columns/types/PK/FK; format="sql" returns a self-contained, runnable DDL script (tables, sequences, PK/FK/UNIQUE/CHECK, indexes, trigger functions, triggers) — no extra tools required. Pass output_dir to write {database}_schema_{UTC}.{json,sql} instead of returning it inline (recommended for large DBs). |
dump_schema_faithful | export | Byte-faithful schema dump via the database's own pg_dump --schema-only — the most complete/runnable export. Requires the pg_dump binary on the server host; if missing, returns pg_dump_not_found with install guidance (see the faithful_schema_export prompt). |
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. |
get_object_definition | explore | Faithful SQL definition of a view / function / trigger / sequence / index by name (native pg_get_*def; overloads and all schemas returned). |
execute_read_query | execute | Run a single read-only statement (SELECT/WITH/…) inside a read-only transaction. Optional params (real bind parameters via $1/$2 — no quoting pitfalls) and timeout_ms. |
execute_write_query | execute | Run a mutation — gated by the safety model above. Defaults to dry_run=true: execute in a transaction, report would-be rows_affected, always ROLL BACK — show the user real impact before consenting to the real write. Committing (dry_run=false) requires a prior preview of the identical statement, which expires after 10 minutes and is consumed by its commit; pass skip_dry_run=true only when the user explicitly asks to skip the preview. Also takes params/timeout_ms. |
explain_query | execute | EXPLAIN (optionally ANALYZE) a validated read-only query — confirm index usage without any write access. |
cancel_query | execute | Cancel the statement in a given backend pid (native pg_cancel_backend); the session survives. Find pids via show_activity. |
open_query_cursor | cursor | Open a server-side cursor over a read-only query for large result sets; returns a cursor_id. Max 5 open; 15-min idle auto-reap. |
fetch_rows | cursor | Fetch the next N rows from an open cursor; auto-closes when drained. |
close_cursor | cursor | Close a cursor and release its connection (idempotent). |
diff_schemas | insight | Structural schema diff between two configured databases (tables, columns, types, defaults, PK/FK) — verify a migrated copy matches its source. |
check_sequences | insight | Find sequences behind their column's max value (the silent post-migration breakage); fix with setval(). |
table_stats | insight | Approximate row counts + disk/index sizes per table, largest first (statistics only, no scans). |
show_activity | insight | Sanitized pg_stat_activity: pid, state, wait events, query age — no user names, client addresses, or query text (text is opt-in and truncated). |
set_yolo_mode | config | Enable/disable yolo for one database (persisted). |
check_database | doctor | Test one database (or all) → OK or a sanitized diagnostic; reports active_port when a fallback port answered, and failed_port on an UNREACHABLE row when the failure that ended the probe chain (auth, TLS, DB-not-found, …) came from a probed fallback port rather than the primary. |
doctor | doctor | Diagnose the whole setup, not just connectivity: stale running server processes, a newer PyPI release, connections.json key typos/wrong types, secrets exposure (file permissions, git), MCP client entries pointing at dead paths, and per-database connectivity with a credential-free fallback-port identity probe. Returns {check, status, detail, suggested_action} rows; offline=true skips the PyPI lookup. |
Prompts:
troubleshoot_connection — a discoverable, full connection-gotchas checklist (host/port, firewall, sslmode, Docker localhost, db-name case, pool limits, …).faithful_schema_export — how to choose between the self-contained SQL export and the faithful pg_dump one, including how to offer installing pg_dump.
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). Run directly in a terminal it prints guidance and exits — it does not hang. |
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 (including fallback_ports where configured) 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 doctor | Diagnose the whole setup — stale processes, a newer release, config-schema typos, secrets exposure, client entries, connectivity (exit 0 if nothing failed, 2 if any check fails). --offline skips only the PyPI version lookup; the database probes still run. |
db-conn-mcp remove <name> | Remove one connection. |
db-conn-mcp reset | Remove all connections (delete connections.json) — fresh slate. |
db-conn-mcp yolo <name> on|off | Toggle yolo for one database. |
db-conn-mcp -v / --version | Print the installed version and the exact build commit, then exit. |
--config <path> works before or after any subcommand.
Optional dependency: the doctor's process_staleness check needs psutil to inspect running processes. It is not required — without it that one check reports skipped and every other check runs normally. To enable it, install the doctor extra — pip install "db-conn-mcp[doctor]" (or pipx install "db-conn-mcp[doctor]") — or, for an install you already have via pipx, pipx inject db-conn-mcp psutil.
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
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, doctor, clients, handlers, server, cli); only the dialect layer knows a specific database exists. See docs/ARCHITECTURE.md, docs/PRD.md, and docs/PLAN.md.
Star this repo
If db-conn-mcp saved you time, a ⭐ helps other people find it — it's the only signal that surfaces a small self-hosted tool. Star it here.
License
MIT — see LICENSE.