claude-chill/README.md

claude-chill

A PTY proxy that tames Claude Code's massive terminal updates.

The Problem

Claude Code uses synchronized output to update the terminal atomically. It wraps output in sync markers (\x1b[?2026h ... \x1b[?2026l) so the terminal renders everything at once without flicker.

The problem: Claude Code sends entire screen redraws in these sync blocks - often thousands of lines. Your terminal receives a 5000-line atomic update when only 20 lines are visible. This causes lag, flicker, and makes scrollback useless since each update clears history.

Analysis of terminal recordings confirms Claude Code wraps 100% of its output in sync blocks - every byte of visible output goes through synchronized updates.

Sync blocks start with one of three patterns (from a 3.5GB recording sample):

Pattern	Count	Frequency	Avg Size
Line clearing (2K + 1A repeated)	3,544	55%	2.7 KB
Full screen clear (2J + 3J + H)	2,891	45%	94.5 KB
CRLF + color codes	1	<1%	2.0 KB

The full screen clears are 35x larger than incremental line clears - these are the real problem.

The Solution

claude-chill sits between your terminal and Claude Code:

1. Intercepts sync blocks - Catches those massive atomic updates
2. Truncates full screen clears - Only the 45% that are full redraws (94.5 KB avg) get truncated to the last N lines (default: 100). The 55% incremental updates (2.7 KB avg) pass through unchanged.
3. Preserves history - Accumulates content in a buffer. Clears on full screen clear, accumulates otherwise.
4. Enables lookback - Press a key to pause Claude and view the full history buffer

Installation

cargo install --path crates/claude-chill

Usage

claude-chill claude
claude-chill -- claude --verbose   # Use -- for command flags
claude-chill -l 50 -- claude       # Set max lines to 50

Lookback Mode

Press Ctrl+6 (or your configured key) to enter lookback mode:

1. Claude pauses - Output from Claude is cached, input is blocked
2. History dumps - The full history buffer is written to your terminal
3. Scroll freely - Use your terminal's scrollback to review everything
4. Exit - Press the lookback key again or Ctrl+C to resume

When you exit lookback mode, any cached output is processed and the current state is displayed.

Configuration

Create ~/.config/claude-chill.toml:

max_lines = 100        # Lines shown per sync block
history_lines = 100000 # Lines stored for lookback
lookback_key = "[ctrl][6]"

Key Format

[modifier][key] - Examples: [f12], [ctrl][g], [ctrl][shift][j]

Modifiers: [ctrl], [shift], [alt]

Keys: [a]-[z], [f1]-[f12], [pageup], [pagedown], [home], [end], [enter], [tab], [space], [esc]

Why Ctrl+6?

Ctrl+6 sends 0x1E, a control character not frequently used by terminals, signals, or shells. Avoid Ctrl+letter hotkeys - terminals can't distinguish Ctrl+J from Ctrl+Shift+J.

How It Works

claude-chill creates a pseudo-terminal (PTY) and spawns Claude Code as a child process. It then acts as a transparent proxy between your terminal and Claude:

┌──────────────┐     ┌──────────────┐     ┌──────────────┐
│   Terminal   │◄───►│ claude-chill │◄───►│  Claude Code │
│   (stdin/    │     │   (proxy)    │     │   (child)    │
│    stdout)   │     │              │     │              │
└──────────────┘     └──────────────┘     └──────────────┘

1. Input handling: Keystrokes pass through to Claude, except for the lookback key which toggles lookback mode
2. Output processing: Scans output for sync block markers. Non-sync output passes through directly
3. Sync block buffering: Accumulates sync block content until the end marker arrives
4. Truncation decision: If the sync block contains a full screen clear (ESC[2J + ESC[H), truncates to the last N lines. Otherwise passes through unchanged
5. History tracking: Maintains a rolling buffer of output for lookback mode
6. Signal forwarding: Window resize (SIGWINCH), interrupt (SIGINT), and terminate (SIGTERM) signals are forwarded to Claude

Disclaimer

This tool was developed for personal convenience. It works for me on Linux and macOS, but it hasn't been extensively tested across different terminals or edge cases. Don't use it to send anyone to space, perform surgery, or run critical infrastructure. If it breaks, you get to keep both pieces.

Contributing

See CONTRIBUTING.md.

License

MIT