deff is a new Rust-based terminal user interface that provides interactive side-by-side git diff review with syntax highlighting and line-level tinting for added and deleted code. The tool supports keyboard and mouse navigation, vim-style motions, and in-diff search functionality, making code review more efficient directly in the terminal.

Built as a TUI application, deff offers multiple comparison strategies including upstream-ahead for comparing local branches against their remote counterparts and explicit range comparisons using --base and --head flags. A standout feature is the --include-uncommitted mode, which lets developers review their working tree before committing, showing exactly what changes will be included.

The tool includes per-file reviewed toggles that persist locally under .git/deff/reviewed/, language-aware syntax highlighting, and independent horizontal scrolling for each pane. Users can navigate with familiar vim commands (h/j/k/l, g/G, Ctrl+u/Ctrl+d) and search within diffs using the / key followed by n/N to jump between matches.