What it is
Express is a minimal web framework for Node.js. It maps HTTP methods and paths to handler functions and runs each request through a chain of middleware for things like body parsing, authentication, logging and error handling. It was created by TJ Holowaychuk and is now part of the OpenJS Foundation, and it remains the most familiar Node web framework.
Express gives structure without imposing much. There is no built-in database layer or folder layout, so it fits APIs where the developer wants to decide exactly how data, validation and tenancy are handled. Many larger Node frameworks are built on top of it, and most Node developers can read an Express codebase on day one.
How I use it
- Lend Pilot's API is Node and Express, backed by PostgreSQL with row-level multi-tenancy.
- Runs in Docker Compose on its own EC2 instance behind nginx, with Let's Encrypt TLS on the origin.
- JWT authentication for the API.
- Every dollar figure comes from deterministic code. Claude reads borrower documents, but the math stays in the API.
Express is the right tool for a JSON API where the business rules are the hard part and the framework should stay out of the way. I use it in Lend Pilot because qualification arithmetic and tenant separation need to be explicit code I can read and test.
Questions
Is Express suitable for financial software?
It is a thin layer, so the safety comes from how the API is written. In Lend Pilot every dollar figure is computed by deterministic code, and AI is kept to reading documents.
How is a multi-tenant Express API kept separate per lender?
Lend Pilot uses row-level multi-tenancy in PostgreSQL, so each lender's records are scoped to that lender.