Claude Code Theme Auto-Switch Patch

Patches the Claude Code binary so the "auto" theme reactively follows terminal dark/light mode during a running session — on macOS, Linux, through SSH, and through tmux.

Without this patch, Claude Code's built-in "auto" theme only checks the OS appearance at startup. If you switch from light to dark mode mid-session, the UI stays on the old theme until you restart.

One-click install

curl -fsSL https://raw.githubusercontent.com/antonioacg/claude-code-theme-patch/main/install.sh | bash

Then restart Claude Code.

Options

Standard themes (hardcoded RGB) instead of ANSI:

curl -fsSL https://raw.githubusercontent.com/antonioacg/claude-code-theme-patch/main/install.sh | THEME_STYLE=standard bash

Check status:

curl -fsSL .../install.sh | bash -s -- --check

Restore original:

curl -fsSL .../install.sh | bash -s -- --restore

Theme styles

The installer ships two detect-theme variants:

Style	Themes	Best for
ansi (default)	dark-ansi / light-ansi	Terminals that auto-switch color palettes (Ghostty, iTerm2, WezTerm)
standard	dark / light	Fixed-palette terminals or when you want Claude's built-in RGB colors

ANSI themes use your terminal's color palette, so they look correct regardless of which palette is active. Standard themes use hardcoded RGB values that may clash with your terminal's background after a switch.

To switch styles after installing, copy the desired variant over the installed script:

# Switch to ANSI
cp detect-theme-ansi ~/.claude/detect-theme

# Switch to standard
cp detect-theme-standard ~/.claude/detect-theme

How it works

Two components:

1. Binary patch — polling interval

The theme provider's React useEffect hook is patched from a no-op to a 5-second polling interval:

// Original — empty, does nothing
WDT.useEffect(() => {}, [z]);

// Patched — polls terminal theme every 5 seconds when theme is "auto"
WDT.useEffect(() => {
  let t = z == "auto" && setInterval(() => H(pPR()), 5e3);
  return () => clearInterval(t);
}, [z]);

pPR() now calls ~/.claude/detect-theme via execSync instead of the macOS-only defaults read command.

2. detect-theme script — OSC 11 terminal query

A small shell script at ~/.claude/detect-theme that:

1. macOS fast path: uses defaults read -g AppleInterfaceStyle (instant, no TTY needed)
2. OSC 11 fallback: opens /dev/tty and sends the OSC 11 escape sequence (\033]11;?\033\\). The terminal responds with its current background color as rgb:RRRR/GGGG/BBBB. Computes luminance and prints the appropriate theme name.

This queries the terminal directly — not the OS. It works:

• macOS — Ghostty, iTerm2, WezTerm, Kitty, Terminal.app
• Linux — any terminal with OSC 11 support
• Through SSH — escape sequences travel through the PTY
• Through tmux — tmux 3.4+ natively forwards OSC 11 to the outer terminal

Byte-budget technique

The Bun-compiled binary embeds JS source at a fixed offset. The replacement must be exactly the same byte length. Compressions used:

Compression	Bytes saved
=== → == (8 string comparisons)	8
!==null → !=null (2 occurrences)	2
spawnSync + result parsing → execSync of external script	46
Pu_===void 0 → ??= operator	22
function $k6(){return pPR()} → var $k6=pPR;	16
Total saved	94
Interval code + script path added	−78
Net surplus (padded with spaces)	16

After patching, the binary is ad-hoc re-signed with codesign -s - on macOS.

Requirements

• Python 3.10+
• A terminal with OSC 11 support (most modern terminals)
• Claude Code installed as a compiled binary (official install, mise, or standalone download)

Manual usage

# Apply the patch (patches binary + installs detect-theme script)
python3 patch-theme.py

# Preview without modifying
python3 patch-theme.py --dry-run

# Check current status
python3 patch-theme.py --check

# Restore original binary from backup
python3 patch-theme.py --restore

# Use a specific binary path
python3 patch-theme.py --path /path/to/claude

The patcher automatically:

1. Locates the Claude Code binary (~/.local/share/claude/versions → mise → which → common paths)
2. Installs ~/.claude/detect-theme (detection script)
3. Creates a backup (.backup alongside the binary)
4. Applies the same-length byte replacement
5. Re-signs the binary (macOS only)
6. Sets "theme": "auto" in ~/.claude.json

After Claude Code updates

Updates replace the binary, removing the patch. Re-run the install command or python3 patch-theme.py. The detect-theme script persists across updates.

Remote servers

To patch Claude Code on a remote machine:

# Copy the patcher and detect-theme script
scp -r . user@remote:/tmp/claude-theme-patch/

# SSH in and apply
ssh user@remote 'cd /tmp/claude-theme-patch && python3 patch-theme.py'

The detect-theme script uses OSC 11, so theme detection works through SSH + tmux — it queries the terminal on your local machine, not the remote OS.

Tested versions

Claude Code	Platform	Status	Date	Notes
2.1.76	macOS arm64 (mise)	Tested	2026-03-29	Bun Mach-O, defaults read detection
2.1.86	Linux aarch64 (mise)	Tested	2026-03-30	Bun ELF, COLORFGBG detection
2.1.87	macOS arm64 (mise)	Tested	2026-03-30	Same structure as 2.1.86, different function names
2.1.87	Linux aarch64 (mise)	Tested	2026-03-30	Different names than macOS build of same version
2.1.89	macOS arm64	Tested	2026-04-01	Official install (~/.local/share/claude/versions)

Version differences

The minified JS uses different function names across versions. The patcher maintains patterns for each supported version and auto-detects which one matches.

	v2.1.76	v2.1.86	v2.1.87	v2.1.89
Theme provider	MDT	EGq	E0_	pG_
Cached detect	Jfq	Cd8	IFH	rUH
Raw detect	pPR / $k6	_k5	MR4	uG4
Original method	defaults read	COLORFGBG	COLORFGBG	COLORFGBG
React import	WDT, Ak6, fm	zA	KG	UG
useEffect deps	[z]	[j, J]	[f, w]	[w, f]

How the original code works

Claude Code already supports "auto" as a theme value (not documented). The detection logic:

~/.claude.json: "theme": "auto"
        ↓
    Jfq() — cached detection (runs once at startup)
    Wfq() — fresh detection (runs when user opens /theme picker)
        ↓
    $k6() → pPR() — calls `defaults read -g AppleInterfaceStyle` (macOS only)
        ↓
    Returns "dark" or "light"

The gap: Wfq() only fires when the user interacts with the theme picker. There is no listener for theme changes mid-session. This patch fills that gap with polling, and replaces the macOS-only defaults detection with cross-platform OSC 11.

Available theme values

Claude Code supports six theme values internally:

Value	Label
dark	Dark mode
light	Light mode
dark-daltonized	Dark mode (colorblind-friendly)
light-daltonized	Light mode (colorblind-friendly)
dark-ansi	Dark mode (ANSI colors only)
light-ansi	Light mode (ANSI colors only)

The detect-theme script can return any of these. The detect-theme-ansi variant returns dark-ansi/light-ansi which use the terminal's ANSI color palette — ideal for terminals that auto-switch palettes on theme change.

Context

• Issue #2990 — Automatic light/dark theme selection
• Issue #11813 — System theme support (134+ upvotes)
• OSC 11 comment — Suggested approach using terminal background query
• Helix implementation — Same OSC 11 approach
• Inspired by claude-code-patches

Restoring

# Via the installer
curl -fsSL .../install.sh | bash -s -- --restore

# Via the patcher
python3 patch-theme.py --restore

# Or manually
cp /path/to/claude.backup /path/to/claude

License

MIT