How do you debug a SAP Fiori application?

Since a Fiori app runs as a JavaScript application in the browser, debugging combines standard web development tools with SAP-specific diagnostics for the backend OData layer it talks to.

1. Browser developer tools (F12) — inspect network requests to see the actual OData calls being made and their responses, set JavaScript breakpoints in the SAPUI5 controller code, and check the console for client-side errors.
2. UI5 diagnostics tool (built into SAPUI5, accessible via a keyboard shortcut) — shows technical details about the running app, including loaded libraries, control tree, and OData model state.
3. Backend-side debugging — if the issue is actually in the OData service or underlying business logic (not the frontend), the ABAP debugger (with an external/session breakpoint set on the relevant service implementation or behavior definition method) lets you step through what happens when the Fiori app's request reaches the backend.

A common troubleshooting sequence is checking the browser's network tab first to see the actual request/ response, which usually reveals whether the problem is a frontend logic issue or something the backend service itself is returning incorrectly — pointing you toward which of the above tools to reach for next.