contextshrink-claude

ContextShrink Code for Claude Code. It trims what Claude Code resends on every turn, so each 5-hour window on your Claude plan goes further. It runs on your computer. Windows is supported today; macOS and Linux are coming.

Use

npx contextshrink-claude

Your browser opens so you can approve this computer (sign in to ContextShrink, then approve the code shown). Then the command installs a local engine, points Claude Code at it, and sets up the Claude Desktop Code tab if Claude Desktop is installed. Start a new Claude Code session afterwards.

You need Windows 10 or 11, Node.js 18 or newer, and Claude Code. Your Claude sign-in is not touched.

Price and devices

• 7 days free, no card needed. Then $5 a month. Cancel anytime.
• Without an active free week or subscription, compression stops and Claude works normally. Claude never stops working.
• Up to 2 devices per account. A third device is refused with the two connected devices named. Disconnect one, then run the command again.

Privacy

Your prompts never leave your computer. Compression runs on your machine, and requests go straight to Anthropic. ContextShrink never sees or stores your prompts, your code, or your Claude sign-in. It only receives the device registration, plan checks, and hourly usage counts (numbers only).

Commands

npx contextshrink-claude [connect] [--force] [--no-code-tab]
npx contextshrink-claude status
npx contextshrink-claude uninstall
npx contextshrink-claude lean on [--force]
npx contextshrink-claude lean off
npx contextshrink-claude lean status

• connect (the default) signs this computer in and sets everything up. --force replaces another gateway or an existing ANTHROPIC_CUSTOM_HEADERS; uninstall puts them back. --no-code-tab skips the Claude Desktop Code tab.
• status shows this device, the plan and free-week days left, whether the engine is running, and the usage saved today.
• uninstall restores Claude Code's settings and the Code tab. When no ContextShrink tool is left on this computer, it also releases the device, stops the engine and deletes the engine files, the logs and the records of earlier versions. It ends with Nothing from ContextShrink is left on this computer., or lists what remains and why (exit code 1). disconnect and logout do the same.

Keep sessions lean

Connect turns this on by default: it caps Claude Code's auto-compact window at 200,000 tokens. A long session is then summarised instead of resending about 1M tokens of context on every turn, so a subscription plan goes further. The cost: older history becomes a summary. The value is set in settings.json and, when npx owns the Code tab, in codetab.json. Start a new Claude Code session (or restart Claude Desktop) afterwards.

• lean off puts back the value that was there before and is remembered: later connects leave it off. lean on turns it back on. uninstall removes the setting and the choice, even when the connection record cannot be read.
• A CLAUDE_CODE_AUTO_COMPACT_WINDOW you set yourself is kept by connect, and lean on refuses to replace it unless you add --force.
• The desktop app's Code tab is never changed.

What it changes

• ~/.claude/settings.json: ANTHROPIC_BASE_URL points at the local engine (http://127.0.0.1:18793); ENABLE_TOOL_SEARCH is set to "true" unless you set it; a SessionStart hook starts the engine; the status line shows usage saved today.
• A Startup shortcut, ContextShrink Engine.lnk, starts the engine when you sign in.
• The engine, in %LOCALAPPDATA%\ContextShrink\engine\<version>.
• Device files in ~/.contextshrink: device.json (the device key, readable only by you), license.json (the plan note) and usage-pending.json (usage counts not yet sent).
• On Windows with Claude Desktop, the Code tab routing (see codetab.json). If the ContextShrink desktop app is installed but its Code-tab routing is off, connect routes the Code tab through the engine. Uninstall hands the desktop app's codetab.json back byte for byte (npx-takeover.json keeps the copy), unless the app changed it since.

Every setting connect changes is recorded, so uninstall restores exactly what it changed. A value you edit after connecting is left alone, and uninstall says so.

Upgrading from 0.2.x

Run npx contextshrink-claude once. It signs this computer in and replaces the account key in settings with the engine address. The old account key is no longer used. Revoke it on the API Keys page.

When it refuses

• A copy older than the latest release: npx can run an old cached copy of an unversioned command. Every command says so, and connect and lean on refuse with exit code 4 and the line to run (npx contextshrink-claude@latest), so an old copy never installs an old engine. Set CONTEXTSHRINK_NO_UPDATE_CHECK=1 to turn the check off.
• An older copy installed with npm install contextshrink-claude in the folder you run from: a plain npx contextshrink-claude runs that copy instead of the latest release. A newer copy names it; remove it in that folder with npm uninstall contextshrink-claude.
• Not Windows: ContextShrink Code runs on Windows today.
• Another gateway is set in ANTHROPIC_BASE_URL, or ANTHROPIC_CUSTOM_HEADERS is set: use --force to replace it, or remove it yourself.
• Claude Code settings changed since connect: run uninstall to restore them, then connect again.
• Two devices are already connected (exit code 3): run uninstall on one of them, or remove it at https://code.contextshrink.com/account.
• The engine download does not match its published size and SHA-256, or its Windows signature is not valid: nothing is installed.
• The engine does not start: Claude Code's settings are not changed.

Development

Tests use node:test, with npm test. They run against a fake ContextShrink API and a fake engine on 127.0.0.1. Every path lives in a temp folder, and the Windows steps (browser, signature check, unzip, shortcut) use a fake adapter, so no test reads your real ~/.claude or runs PowerShell. Test runs are serialized (--test-concurrency=1, Node 20.10 or newer).

Set CONTEXTSHRINK_API_URL, CONTEXTSHRINK_ENGINE_URL and CONTEXTSHRINK_HOME to point the CLI elsewhere. Test-only overrides (CONTEXTSHRINK_NPX_TEST=1 and CONTEXTSHRINK_NPX_*) are ignored unless CONTEXTSHRINK_NPX_TEST=1 is set.