connect_db
Connect to PostgreSQL database. Only use when no default connection exists
LABSCO SUMMARY
Read-only by default, and enforced twice: the write tool is not registered and the database session refuses writes.
Plenty of database servers offer a read-only mode. Here readonly is the default and it holds at two levels: the write tool, execute, is not registered at all, and the PostgreSQL session itself runs with default_transaction_read_only on. Writes come back only when someone starts it with --access-mode dml or full, or sets PG_ACCESS_MODE — so that flag, and a least-privilege database role for each mode, are what to check before a model that will eventually try to fix a problem by writing gets near production. The three introspection tools are what make the read side actually usable — an agent that can read the schema writes a query that runs, and one that cannot writes a query about columns it imagined.
What it is
A PostgreSQL client that starts in read-only mode with five tools: connect, query, and three that describe the database — schemas, tables and a single table's structure. A sixth, execute, is registered only in dml or full mode.
What you get
- query accepts SELECT, WITH, EXPLAIN and SHOW, and nothing else; in the default readonly mode there is no write tool at all.
- list_schemas, list_tables and describe_table give an agent the structure it needs to write a correct query instead of guessing at column names.
- connect_db is documented as being for the case where no default connection exists, so the normal path is configured rather than passed per call.
Requirements
A PostgreSQL connection, normally configured as the default rather than supplied per call.
Setup effort
One command plus credentials — npx mcp-postgres-secure --access-mode readonly, then supply credentials
USE CASES
01
Getting oriented in a database you did not design
List the schemas, then the tables, then read one table's structure — enough to write a query that references real columns.
02
Answering a question from the data
Run the SELECT or WITH query, using EXPLAIN first when the shape of the plan matters more than the rows.
03
Letting an agent near production data
Run it in the default readonly mode under a read-only database role: execute is not registered and the session itself refuses writes. Just never start it with --access-mode dml or full.
5 tools
Counted once with only startup setup. Other versions, modes or optional credentials may expose a different list.
describe_table
Get table structure
list_schemas
List all schemas in the database
list_tables
List tables in the database
query
Execute a read-only SQL query (SELECT, WITH, EXPLAIN, SHOW)
BEFORE YOU INSTALL
What to know first
Tools you get
5 tools when we connected; the project documents 6. The missing one is execute, the only write tool; it appears with --access-mode dml or --access-mode full, or PG_ACCESS_MODE. connect_db disappears when PG_LOCK_CONNECTION is on, the default when the connection comes from environment variables.
Requires
- npx on PATH
- PG_PASSWORD in your environment
- PG_USER in your environment
Where it runs
All 3 documented setups run the server on your machine.
INSTALLATION
Connect your client
Server setup
TERMINAL
npx mcp-postgres-secure --access-mode readonlyMCP Clients
Any MCP client — read-only
ANY MCP CLIENT — READ-ONLY · JSON
{
"mcpServers": {
"postgres-readonly": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"mcp-postgres-secure",
"--access-mode",
"readonly"
],
"env": {
"PG_HOST": "localhost",
"PG_PORT": "5432",
"PG_USER": "mcp_readonly",
"PG_PASSWORD": "<YOUR_PG_PASSWORD>",
"PG_DATABASE": "<YOUR_PG_DATABASE>",
"PG_LOCK_CONNECTION": "true"
}
}
}
}Any MCP client — read + DML
ANY MCP CLIENT — READ + DML · JSON
{
"mcpServers": {
"postgres-dml": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"mcp-postgres-secure",
"--access-mode",
"dml"
],
"env": {
"PG_HOST": "localhost",
"PG_PORT": "5432",
"PG_USER": "mcp_dml",
"PG_PASSWORD": "<YOUR_PG_PASSWORD>",
"PG_DATABASE": "<YOUR_PG_DATABASE>",
"PG_LOCK_CONNECTION": "true"
}
}
}
}Any MCP client — full access
ANY MCP CLIENT — FULL ACCESS · JSON
{
"mcpServers": {
"postgres-full": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"mcp-postgres-secure",
"--access-mode",
"full"
],
"env": {
"PG_HOST": "localhost",
"PG_PORT": "5432",
"PG_USER": "mcp_admin",
"PG_PASSWORD": "<YOUR_PG_PASSWORD>",
"PG_DATABASE": "<YOUR_PG_DATABASE>",
"PG_LOCK_CONNECTION": "true"
}
}
}
}
