Claude/Code/Q/Why can't I scroll up in tmux copy mode when Claude Code is in TUI mode?

• Why can't I scroll up in tmux copy mode when Claude/Code is in TUI mode? card

  • My Answer

    • when claude is in /tui fullscreen mode, it uses an off-screen render buffer, which interferes with tmux
    • inside of claude, use /tui default to disable Claude/Code/TUI mode.

  • AI Answer

    • AI/Response
    • Short answer: Claude/Code TUI mode activates the terminal alternate screen buffer, which never writes to tmux's main scrollback — so copy mode has nothing to scroll through.
    • How the alternate screen buffer works:
      • TUI applications (vim, less, htop, Claude Code) activate the alternate screen on entry via the smcup terminal capability and restore the original screen via rmcup on exit.
      • The alternate screen is a completely separate display area; output written there never flows into tmux's main pane scrollback buffer.
      • tmux copy mode only scrolls through main pane scrollback, so it sees nothing rendered during the TUI session.
    • Workarounds:
      • export CLAUDE_CODE_DISABLE_ALTERNATE_SCREEN=1 — disables the alternate screen; the inline/scrollback renderer is used instead and conversation output flows normally into tmux scrollback.
      • Use Claude Code TUI's built-in navigation: Page Up/Page Down, arrow keys, and mouse scroll work within the TUI view itself.
    • Sources: Claude Code — environment variables