Isthmus

Name: Isthmus
Author: guillermoBallester

@guillermoBallester

About Isthmus

A single binary MCP server that gives Claude, Cursor, and any MCP client safe, read-only access to your PostgreSQL database. Runs locally over stdio or HTTP — your credentials never leave your machine.

#postgresdb #masking #mcpserver

Basic information

Config

Add this server to your MCP-compatible client using the configuration below.

{
  "mcpServers": {
    "isthmus": {
      "command": "isthmus",
      "env": {
        "DATABASE_URL": "postgres://user:pass@localhost:5432/mydb"
      }
    }
  }
}

Tools

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Overview

What is Isthmus?

Isthmus is a local MCP server that gives AI models safe, read-only access to your PostgreSQL database. It runs as a single binary on your machine; credentials never leave.

How to use Isthmus?

Install Isthmus via the install script or Docker, set the DATABASE_URL environment variable, and add it to your MCP client configuration (e.g., Claude Desktop JSON). Then ask your AI questions about your database.

Key features of Isthmus

Schema discovery and table description tools
Read-only queries with server-side row limits and timeouts
Column masking for PII (redact, hash, partial, null)
Policy engine that enriches schema with business context
SQL validation via AST-level whitelist (only SELECT/EXPLAIN allowed)
HTTP transport for web-based clients and remote access
OpenTelemetry support for distributed tracing and metrics
Works with Claude Desktop, Cursor, Windsurf, VS Code, and ChatGPT Desktop

Use cases of Isthmus

Allow an AI assistant to explore and query your PostgreSQL schema without write access
Enable safe database analysis in client applications by enforcing read-only queries
Protect sensitive PII data by masking columns before results reach the AI
Give AI models business context on schema objects so they generate more accurate SQL