Cross-Platform Hooks for Claude Code

Problem: A hook you shipped from Windows via cmd /c or PowerShell lights up red the moment a Linux teammate opens the repo. The workaround most people land on is ugly. Three shim scripts per hook: a .cmd for Windows, a .sh for Linux, a .ps1 for PowerShell. All three do exactly the same thing, which is call the .mjs file that actually matters.

Quick Win: Throw the wrappers away. Point the hook config at Node.js directly:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Write|Edit",
        "hooks": [
          {
            "type": "command",
            "command": "node .claude/hooks/formatter.mjs"
          }
        ]
      }
    ]
  }
}

Runs on Windows, Linux, and macOS without changes. node is always on the $PATH because Claude Code lists Node.js as a hard requirement.

Why Hooks Break When the OS Changes

If nobody else touches your setup, none of this bites. Trouble begins the moment .claude/settings.json gets shared, the repo goes public, or you start alternating between a Windows tower and a macOS laptop. The second bash or powershell appears inside a command, half the team cannot run it.

Most tutorials go platform-specific anyway:

// Windows-only
"command": "cmd /c \".claude\\hooks\\formatter.cmd\""
 
// Linux-only
"command": "bash .claude/hooks/formatter.sh"
 
// PowerShell-only
"command": "powershell -NoProfile -File .claude/hooks/statusline.ps1"

Each of those wrappers is two lines of boilerplate around a node call. Three files, three platforms, same job on all of them. If the only layer that knows about the OS is the shim, you can delete the shim.

The Universal Pattern in settings.json

Hooks inside settings.json share one shape:

{
  "statusLine": {
    "type": "command",
    "command": "node .claude/hooks/statusline-monitor.mjs"
  },
  "hooks": {
    "UserPromptSubmit": [
      {
        "hooks": [
          {
            "type": "command",
            "command": "node .claude/hooks/skill-activation.mjs"
          }
        ]
      }
    ],
    "PreCompact": [
      {
        "hooks": [
          {
            "type": "command",
            "command": "node .claude/hooks/backup.mjs",
            "async": true
          }
        ]
      }
    ]
  }
}

No cmd /c. No bash. No powershell. Just node. Every hook type takes the same shape, so PostToolUse, SessionStart/SessionEnd, Stop, and all 12 lifecycle events wire up identically.

Three Rules for Cross-Platform Hook Logic

Inside each .mjs file, three habits keep the logic portable no matter which OS ends up running it.

Use `os.homedir()` Instead of Platform Variables

import { homedir } from "os";
import { join } from "path";
 
// Cross-platform: resolves to C:\Users\you or /home/you
const settingsPath = join(homedir(), ".claude", "settings.json");

Keep $HOME, $env:USERPROFILE, and %USERPROFILE% out of the source. Let the helper pick the right one.

Use `os.tmpdir()` for Temporary File Paths

import { tmpdir } from "os";
import { join } from "path";
 
// Cross-platform: resolves to C:\Users\you\AppData\Local\Temp or /tmp
const cacheFile = join(tmpdir(), "my-hook-cache.json");

Do not reach for /tmp or $env:TEMP by hand.

Use `path.join()` for All File Path Construction

import { join } from "path";
 
// Cross-platform path construction
const logFile = join(".claude", "hooks", "logs", "hook.log");

Stop gluing paths together with / or \\ by hand. Node.js already knows the right separator for whichever OS the hook lands on.

Permissions That Cover Both Platforms

The permissions block in settings.json should hold the Windows name and the Unix name side by side:

{
  "permissions": {
    "allow": [
      "Bash(where:*)",
      "Bash(which:*)",
      "Bash(tasklist:*)",
      "Bash(ps:*)",
      "Bash(taskkill:*)",
      "Bash(kill:*)",
      "Bash(findstr:*)",
      "Bash(node:*)"
    ]
  }
}

Whichever command is not installed on the current machine stays silent. Listing both has no cost, and your hook picks whichever one actually exists without tripping a permission dialog. For deeper automation on this side, see the Permission Hook guide.

Complete Example: Cross-Platform File Logger

One full hook, portable as-is. The job is a file logger. Any Write or Edit that Claude performs gets appended to a log:

#!/usr/bin/env node
import { readFileSync, appendFileSync, mkdirSync } from "fs";
import { join } from "path";
 
const logDir = join(".claude", "hooks", "logs");
mkdirSync(logDir, { recursive: true });
 
try {
  const input = JSON.parse(readFileSync(0, "utf-8"));
  const toolName = input.tool_name;
  const filePath = input.tool_input?.file_path || "unknown";
  const timestamp = new Date().toISOString();
 
  appendFileSync(
    join(logDir, "file-changes.log"),
    `${timestamp} | ${toolName} | ${filePath}\n`,
  );
} catch {
  // Silent fail -- don't block Claude
}
 
process.exit(0);

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Write|Edit",
        "hooks": [
          {
            "type": "command",
            "command": "node .claude/hooks/file-logger.mjs"
          }
        ]
      }
    ]
  }
}

Same behavior on Windows 11, Arch Linux, and macOS Sequoia. Zero wrappers.

Debugging When One OS Breaks

Got a hook that runs on one machine and fails on the next? Walk this list top to bottom:

Hardcoded path separators. Search every .mjs file for / or \\ appearing inside a path. Hand those cases to path.join().
Environment variable references. Look for process.env.HOME, process.env.USERPROFILE, or process.env.TEMP and swap each one out for os.homedir() or os.tmpdir().
Shell-specific commands in settings.json. Any command entry that mentions bash, cmd, powershell, or sh breaks everywhere except its home OS. Point it at node.

Fire the hook manually so the failure cannot hide:

echo '{"tool_name":"Write","tool_input":{"file_path":"test.js"}}' | node .claude/hooks/your-hook.mjs
echo $?  # Should output 0

A 0 on one OS and something else on the next points you at the .mjs file's path handling, never the hook entry in settings.

Release Checklist

Run through this list before a team rollout or a public release:

Every command in settings.json points at node, not cmd, powershell, or bash
Home directories come from os.homedir(), never $HOME or %USERPROFILE%
Temp paths come from os.tmpdir(), never /tmp or $env:TEMP
Paths get built with path.join(), not hand-typed separators
Permissions list both the Windows and the Unix equivalents
The statusLine command resolves to node, not powershell

One file. Three platforms. No upkeep.

Do Claude Code hooks work on Windows?

Yes. Call them through node rather than a shell that only lives on one OS, and they run the same on Windows, Linux, and macOS. Node.js is a hard requirement of Claude Code on every platform, so node is always on the $PATH. Put node .claude/hooks/your-hook.mjs in settings.json and you get identical behavior on all three.

Can I use Python instead of Node.js for hooks?

Python works too, provided every teammate already has an interpreter on their machine. In the command field, reach for python3 rather than python, because certain Linux distros never ship a plain python. Node.js stays the safer pick: Claude Code promises it on every platform, Python it does not.

How do I handle line endings across platforms?

You mostly do not. readFileSync and writeFileSync already normalize the endings. Every hook reads JSON off stdin, and the JSON parser does not care whether the newlines are CRLF or LF. The exception is any hook that emits its own shell script. For that path, write \n and leave the rest to Git's autocrlf setting.

Cross-Platform Hooks for Claude Code

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