oyo

A diff viewer that works two ways: step through changes or review a classic scrollable diff.

https://github.com/user-attachments/assets/0f43b54b-69fe-4cf3-9221-a7749872342b

oyo extends traditional diffs with an optional step-through mode. Use it like a normal diff viewer with scrolling and hunk navigation, or step through changes one at a time and watch the code evolve. You can switch between both modes at any time.

Two ways to use oyo

1. Classic diff (scroll-only)

Review all changes at once, scroll freely, and jump between hunks, just like a traditional diff viewer.

• Scroll the full diff
• Jump between hunks
• No stepping required

Enable with:

• oy --no-step
• Toggle in-TUI with s
• Set stepping = false in config

2. Step-through review (default)

Apply changes incrementally and watch the file transform from old to new.

• Step change-by-change
• See precise evolution of the code
• Useful for large refactors or careful reviews

oyo does not replace classic diffs, it adds a new way to review them.

Features

• Classic diff mode (no-step) Scroll the full diff with hunk navigation, no stepping required
• Step-through navigation Move through changes one at a time with keyboard shortcuts
• Hunk navigation Jump between groups of related changes in both modes
• Four view modes:
  • Unified: Watch the code morph from old to new state
  • Split: See old and new versions with synchronized stepping
  • Evolution: Watch the file evolve, deletions simply disappear
  • Blame: Per-line git blame gutter (opt-in)
• Inline review comments: Add/update/remove line and hunk comments across views; printed to stdout on quit
• Word-level diffing: See exactly which words changed within a line
• Multi-file support: Navigate between changed files with preserved positions
• Search: Regex search with to jump between matches
• Syntax highlighting: Toggle on/off for code-aware coloring (auto-enabled in no-step mode)
• Blame hints: One-shot or toggle blame previews while stepping (opt-in)
• Command palette: Search for commands and files without leaving the diff
• Line wrap: Toggle wrapping for long lines
• Fold unchanged blocks: Toggle to collapse long context sections
• Animated transitions: Smooth fade in/out animations as changes are applied
• Playback: Automatically step through all changes at a configurable speed
• Git integration: Works as a git external diff tool or standalone
• Commit picker: Browse recent commits and pick ranges interactively (oy view)
• Themes: Built-in themes plus .tmTheme syntax themes (configurable, with light/dark variants)
• Configurable: XDG config file support for customization

Installation

npm (macOS, Linux)

npm i -g @ahkohd/oyo

Pi package (/diff, /review commands)

pi install npm:@ahkohd/pi-oyo

Homebrew (macOS, Linux)

brew install ahkohd/oyo/oy

AUR (Arch Linux)

paru -S oyo

Cargo

cargo install oyo --locked --force

Usage

Classic diff (scroll-only)

oy --no-step
# or toggle in-app with `s`

Step-through diff

oy

Compare files

oy old.rs new.rs

Compare a file against HEAD

oy path/to/file.rs

Runs a working-tree vs HEAD diff for that file (like git diff path/to/file.rs).

Commit picker

oy view

View modes

oy old.rs new.rs --view split
oy old.rs new.rs --view evolution

Autoplay

oy old.rs new.rs --autoplay
oy old.rs new.rs --speed 100

Git ranges

oy --range HEAD~1..HEAD
oy --range main...feature

Staged changes

oy --staged

Review output

# default: prints review comments to stdout on quit
oy --no-step

# also write review comments to a file
oy --no-step --review-output-file /tmp/oy-review.txt

# file-only output (for tool integrations)
oy --no-step --review-output-file /tmp/oy-review.txt --no-print-review

# ephemeral review session (disable autosave/restore)
oy --no-step --no-review-persist

# start a fresh persisted review session (clear saved state for this diff)
oy --no-step --clear-review-session

Git Integration

Recommended (git difftool)

git difftool -y --tool=oy

~/.gitconfig:

[difftool "oy"]
    cmd = oy "$LOCAL" "$REMOTE"

[difftool]
    prompt = false

[alias]
    d = difftool -y --tool=oy

Note: keep your pager (less, moar, moor) for git diff. Do not set core.pager or interactive.diffFilter to oy.

Jujutsu (jj)

[ui]
paginate = "never"
diff-formatter = ["oy", "$left", "$right"]

[diff-tools.oy]
command = ["oy", "$left", "$right"]

Keyboard Shortcuts

Vim-style counts: Most navigation commands support count prefixes (e.g., 10j moves 10 steps forward, 5J scrolls down 5 lines).

Clipboard support uses system tools: pbcopy (macOS), wl-copy / xclip / xsel (Linux), clip (Windows). Search is case-insensitive regex; invalid patterns fall back to literal matching.

Configuration

Create a config file at ~/.config/oyo/config.toml:

[ui]
auto_center = true          # Auto-center on active change (default: true)
overscroll = false         # EOF overscroll when centering (opt-in)
topbar = true               # Show top bar in diff view (default: true)
view_mode = "unified"       # Default: "unified", "split", "evolution", or "blame"
line_wrap = false           # Wrap long lines (default: false, uses horizontal scroll)
fold_context = "off"        # "off", "on", or "counts"
scrollbar = false           # Show scrollbar (default: false)
strikethrough_deletions = false # Show strikethrough on deleted text
gutter_signs = true         # Show +/- sign column (unified/evolution)
stepping = true             # Enable stepping (false = no-step mode)

[navigation.wrap]
step = "none"               # "none" | "step" | "file"
hunk = "none"               # "none" | "hunk" | "file"
# [ui.diff]
# bg = false                # Full-line diff background (true/false)
# fg = "theme"              # "theme" or "syntax"
# highlight = "text"        # "text" | "word" | "none"
# max_bytes = 16777216      # Defer diffing above this size (bytes)
# full_context_max_bytes = 2097152  # Full-context render up to this size (bytes)
# defer = true              # Defer large diffs and compute in background
# idle_ms = 250             # Idle time before background diff compute
# extent_marker = "neutral" # "neutral" or "diff"
# extent_marker_scope = "progress" # "progress" or "hunk"
# extent_marker_context = false # show extent markers on unchanged lines
# [ui.blame]
# enabled = false           # Show git blame hints (opt-in)
# mode = "one_shot"         # "one_shot" or "toggle"
# hunk_hint = true          # Show blame hint when jumping to a hunk
# [ui.time]
# mode = "relative"         # "relative" | "absolute" | "custom"
# format = "[year]-[month]-[day] [hour]:[minute]" # Used when mode = "custom"
# [ui.split]
# align_lines = false       # Insert blanks to keep split panes aligned
# align_fill = "╱"          # Fill character for aligned blanks (empty = no marker)
# [ui.evo]
# syntax = "context"         # "context" (non-diff only) or "full" (diff + context)
# [ui.unified]
# modified_step_mode = "mixed" # "mixed" or "modified" (unified pane only)
# theme = { name = "tokyonight" } # Built-ins listed below
primary_marker = "▶"        # Marker for primary active line (single-width char recommended)
primary_marker_right = "◀"  # Right pane marker (optional, defaults to ◀)
extent_marker = "▌"         # Left pane extent marker (Left Half Block)
extent_marker_right = "▐"   # Right pane extent marker (optional, defaults to ▐)
zen = false                 # Start in zen mode (minimal UI)

[ui.syntax]
mode = "on"                # "on" or "off"
# theme = "tokyonight"     # builtin name or "custom.tmTheme" (from ~/.config/oyo/themes)
#                           # default: ui.theme.name, fallback to "ansi"
# [ui.syntax.warmup]
# active_lines = 100       # lines per tick while navigating
# pending_lines = 300      # lines per tick while catching up to a pending checkpoint
# idle_lines = 1000        # lines per tick while idle
# debounce_ms = 80         # wait before warming a new viewport target

[playback]
speed = 200                 # Autoplay interval in milliseconds
autoplay = false            # Start with autoplay enabled
animation = false           # Enable fade animations
animation_duration = 150    # Animation duration per phase (ms)
auto_step_on_enter = true   # Auto-step to first change when entering a file
auto_step_blank_files = true # Auto-step when file would be blank at step 0 (new files)

[files]
panel_visible = true        # Show file panel in multi-file mode
panel_width = 30            # File panel width (columns)
counts = "active"           # Per-file +/- counts: active, focused, all, off

[no_step]
auto_jump_on_enter = true   # Jump to first hunk when entering a file in no-step mode

[comments.mentions]
file_scope = "repo"         # "changed" | "repo" (git-aware via ls-files)
finder = "auto"             # "auto" | "builtin" | "fzf"

Example config:

[ui]
zen = false
auto_center = true
overscroll = false
view_mode = "unified"
gutter_signs = false
topbar = true

[ui.blame]
enabled = true

[ui.theme]
name = "tokyonight"

[ui.diff]
fg = "syntax"
bg = true
highlight = "text"
max_bytes = 16777216
full_context_max_bytes = 2097152
defer = true
idle_ms = 250
extent_marker = "diff"
extent_marker_scope = "hunk"

[ui.syntax]
mode = "on"

[ui.evo]
syntax = "full"

[ui.split]
align_lines = true

[playback]
speed = 200
animation = true
animation_duration = 150
autoplay = false

[comments.mentions]
file_scope = "repo"
finder = "auto"

Config is loaded from (in priority order):

1. $XDG_CONFIG_HOME/oyo/config.toml
2. ~/.config/oyo/config.toml
3. Platform-specific (e.g., ~/Library/Application Support/oyo/config.toml on macOS)

Theme and syntax theme configuration is documented in THEME.md.

Diff styling previews are available in DIFF_PREVIEWS.md.

How It Works

Stepping applies changes in file order. The view renders applied changes, highlights the active change, and keeps pending changes muted.

Development

# Build everything
cargo build

# Run tests
cargo test

# Run CLI in development
cargo run --bin oy -- old.rs new.rs