Route groups use parentheses in folder names to organize files without changing the URL. Nested layouts share UI shells across route segments.
Common Interview Questions
Q: What is a route group?
Answer: Folders wrapped in () are omitted from the URL. Useful for splitting layouts or teams without nested paths.
app/
(marketing)/
about/page.tsx → /about
(shop)/
products/page.tsx → /products
Q: Multiple root layouts?
Answer: Different route groups can have their own layout.tsx without sharing a parent — e.g., marketing vs dashboard with different html/body (rare, advanced).
Q: layout.tsx responsibilities?
Answer: Wrap child pages with persistent UI (nav, sidebar). State in layouts persists across navigations within the segment.
Q: template.tsx vs layout.tsx?
Answer: Templates remount on navigation (new key), resetting state. Layouts persist. Use templates for enter animations or keyed state reset.
Key Points for Interviews
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Parentheses folders are organizational only
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Layouts nest automatically down the tree
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Colocate loading.tsx and error.tsx per segment
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Split auth vs public sections with groups
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Do not confuse groups with dynamic [segments]