Shipping Web Applications That Are Still Maintainable in Year Three

The highest-value typing is at the edges: API responses, form input, database rows. Validate untrusted data once at the boundary and the interior of the application becomes far simpler to reason about.

Comments explaining what the code does age badly. Short records of why an approach was chosen — and what was rejected — are what a future maintainer actually needs.

If releasing is stressful, releases become rare, and rare releases are large and risky. Automated, repeatable deployment with a rollback path keeps change cheap.