connect_db
Connect to PostgreSQL database. NOTE: Default connection exists - only use when requested or if other commands fail
LABSCO SUMMARY
The read/write split is in the tool name, so an approval policy can act on it.
query runs SELECT and execute runs INSERT, UPDATE and DELETE, which puts the distinction where a reviewer of tool calls can see it instead of inside an SQL string. The default connection comes from configuration and connect_db is the exception — its own description says to reach for it only when asked or when other commands fail. Schema exploration exists before any SQL is written, which matters on a database nobody on the call has seen.
What it is
A PostgreSQL client of 6 tools that takes its connection from the environment and keeps reads and writes on separate tools.
What you get
- Parameterised reads through query, which takes the SQL text and a params array.
- Writes through execute, covering INSERT, UPDATE and DELETE.
- Schema discovery — list_schemas across the database, list_tables within a schema, describe_table for one table's structure.
- A connection that is already in place from configuration, with connect_db available to point the session at a different host or database.
Requirements
A reachable PostgreSQL database, addressed by PG_HOST, PG_PORT, PG_USER, PG_PASSWORD and PG_DATABASE.
Setup effort
One command plus credentials — npx mcp-postgres-server, then supply credentials
USE CASES
01
Answering a question about live data without opening a client
Find the table, read its structure, and run a parameterised SELECT against it in the same conversation.
02
Correcting a row somebody got wrong in the admin screen
Read the affected rows first, then issue the write as a separate call so the change is visible as a write rather than buried in a query.
03
Working out what a database you inherited contains
Start from the schema list, walk down into tables, and read column structure before writing anything against it.
04
Pointing the session at a second database mid-conversation
Switch the connection to another host or database when the configured default is not the one holding the answer.
6 tools
Counted once with only startup setup. Other versions, modes or optional credentials may expose a different list.
describe_table
Get table structure
execute
Execute an INSERT, UPDATE, or DELETE query
list_schemas
List all schemas in the database
list_tables
List tables in the database
query
Execute a SELECT query
BEFORE YOU INSTALL
What to know first
Tools you get
6 tools when we connected. execute runs INSERT, UPDATE and DELETE and cannot be turned off; query is the SELECT-only counterpart.
Requires
- npx on PATH
- PG_USER in your environment
- PG_PASSWORD in your environment
Where it runs
The documented client runs the server on your machine.
CONTEXT COST
Light Standing cost
Rated by the size of the 6 tool definitions that ride along on every turn, not by how many there are
INSTALLATION
Connect your client
Server setup
TERMINAL
npx mcp-postgres-serverMCP Clients
Any MCP client
ANY MCP CLIENT · JSON
{
"mcpServers": {
"postgres": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"mcp-postgres-server"
],
"env": {
"PG_HOST": "<YOUR_PG_HOST>",
"PG_PORT": "5432",
"PG_USER": "<YOUR_PG_USER>",
"PG_PASSWORD": "<YOUR_PG_PASSWORD>",
"PG_DATABASE": "<YOUR_PG_DATABASE>"
}
}
}
}
