Isthmus

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

FAQ from Isthmus

What databases does Isthmus support?

Isthmus works exclusively with PostgreSQL databases.

Is Isthmus read-only?

Yes. Isthmus only allows SELECT and EXPLAIN statements, enforced via AST-level validation using PostgreSQL’s own parser.

How does Isthmus protect PII?

Column masking allows per-column redact, hash, partial, or null masking, enforced server-side before results are returned.

What transport protocols does Isthmus support?

Isthmus supports stdio (for desktop MCP clients) and HTTP (for web-based clients and remote access).

Which MCP clients are compatible with Isthmus?

Isthmus works with any MCP client, including Claude Desktop, Cursor, Windsurf, Gemini CLI, VS Code, and ChatGPT Desktop.