Spring Boot DevTools speeds up the development inner loop by automatically restarting the application and refreshing the browser whenever code changes are detected.
Key Points: • Uses two classloaders internally so a "restart" only reloads your application's classes, not third-party libraries, making it much faster than a full JVM restart. • LiveReload integration automatically refreshes the browser after a restart, so you don't manually reload. • Automatically disables template caching and other production-oriented caching so changes to templates show up immediately. • Only active when running from an IDE/build tool with the dependency on the classpath -- it's excluded automatically from a repackaged production JAR. • Should never be relied on or included in production builds, since it changes caching and exposes extra information.
Example: Editing a Thymeleaf template or a controller method while the app is running triggers an automatic restart within a couple of seconds, and the browser tab refreshes on its own, instead of requiring a manual stop-rebuild-start cycle.
Interview Tip: A concise interview answer is:
"DevTools gives fast, automatic restarts scoped to just my application's classes, plus LiveReload to refresh the browser, so I see changes within seconds instead of doing a full manual restart. It's development-only -- Spring Boot excludes it from the packaged production JAR automatically, and I make sure it stays that way."