differ

Side-by-side diff review for Claude Code, without leaving your terminal. One keypress to accept or reject — no IDE, no context switch, no friction.

Because you trust Claude. Just not unconditionally.

 original                          │ proposed
 @@ -3,7 +3,6 @@
    3   "I told my wife she was    │    3   "I told my wife she was
    4   drawing her eyebrows too   │    4   drawing her eyebrows too
    5   high. She looked           │    5   high. She looked surprised."
    6   "I'm reading a book        │
    7   about anti-gravity.        │    6   "I'm reading a book about
    8   It's impossible to put     │    7   anti-gravity. It's impossible
[y] accept  [n] reject                                   line 1/12 · hunk 1/1

What it does

Sits between you and Claude. Every time Claude tries to write a file, you see a side-by-side diff in your terminal and get to decide. Claude waits patiently. You press y or n. Life continues.

It implements the Claude Code IDE integration protocol over a local WebSocket — the same protocol VS Code and Emacs use — so Claude thinks it's talking to a proper IDE. It is not.

Requirements

• Node.js ≥ 18
• claude CLI installed (npm install -g @anthropic-ai/claude-code)
• A terminal with TTY support

Install

npm install -g @ittaigolde/differ

The install step also applies a small compatibility fix for node-pty on macOS ARM when needed.

For local development:

cd /path/to/this/repo
npm install
npm link          # makes `differ` available globally

Usage

# In your project directory:
differ

# With a specific workspace:
differ --workspace /path/to/project

# Resume a previous session:
differ --resume <session-id>

# Debug WebSocket traffic (useful if something feels off):
differ --debug /tmp/ws.log

# Debug terminal input handling:
differ --input-debug /tmp/input.log

When --workspace is provided, relative paths from Claude are resolved against that workspace. This lets you launch differ from another directory while still reviewing the right files.

Any arguments after -- are passed directly to claude:

differ -- --model claude-opus-4-7

differ starts Claude with --ide automatically so Claude can connect to the bridge without selecting it from /ide every run.

If Claude does not connect to IDE mode a few seconds after startup, differ prints a one-time warning once the terminal has been idle briefly. This warning means diff review may not be active yet; in Claude, run /ide and select differ, or check that Claude was started with IDE support enabled.

You can also constrain port discovery:

differ --port-min 12000 --port-max 12100

Keys

| Key | Action | |-----|--------| | y | Accept — write the file | | n / Esc | Reject — Claude is notified and can try again | | Ctrl+C | Reject and exit | | j / ↓ | Scroll down | | k / ↑ | Scroll up | | Ctrl+F / Page Down | Page down | | Ctrl+B / Page Up | Page up | | ]c | Next hunk | | [c | Previous hunk |

How it works

1. On startup, writes ~/.claude/ide/<port>.lock — the file Claude Code scans to discover IDEs.
2. Starts a WebSocket server on a free port (default range 10000–65535).
3. Spawns claude in a pseudo-terminal so it gets its own stdin/stdout.
4. When Claude calls openDiff, the response is deferred — Claude blocks — while you review.
5. y sends FILE_SAVED + the new contents. n sends DIFF_REJECTED. Claude continues accordingly.
6. Lock file is removed on exit.

No patches to Claude. No config changes. Nothing persistent except the lock file while running.

Development

Run the test suite with:

npm test

The tests cover protocol response routing, workspace-relative path resolution, and terminal diff row width rendering.

Caveats

• Diagnostics (getDiagnostics) always return empty. Claude may occasionally wonder why your code has no errors. Let it wonder.
• If Claude proposes multiple file changes, they queue up. You review them one at a time.
• Windows, macOS, and Linux should work, subject to node-pty support for your terminal and Node.js version.