Chrome Native Messaging Host Setup

1. Compile the Host Binary

From the project directory:

gcc -o hostapp host.c
chmod +x hostapp

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2. Get Your Extension ID

1. Open Chrome and go to chrome://extensions
2. Enable Developer mode (toggle in the top right)
3. Find your extension — the ID is the 32-character string shown below the extension name

⚠️ If your extension is loaded unpacked without a fixed key in its manifest.json, the ID changes every time you reload it. To pin it, add a key field — see Chrome docs.

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3. Create the Native Messaging Manifest

Create a file named com.ext.nattest.json (must match the name field exactly):

{
  "name": "com.ext.nattest",
  "description": "Native Messaging Host",
  "path": "/absolute/path/to/your/hostapp",
  "type": "stdio",
  "allowed_origins": [
    "chrome-extension://YOUR_EXTENSION_ID_HERE/"
  ]
}

⚠️ path must be absolute. Chrome does not expand ~ or relative paths. Use the full path, e.g. /Users/yourname/nativemessaging/hostapp.

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4. Register the Manifest with Chrome

Copy the manifest to the directory Chrome scans at launch:

cp com.ext.nattest.json \
  ~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/

Platform paths

Browser	Path
Chrome (macOS)	~/Library/Application Support/Google/Chrome/NativeMessagingHosts/
Chrome Canary (macOS)	~/Library/Application Support/Google/Chrome Canary/NativeMessagingHosts/
Chromium (macOS)	~/Library/Application Support/Chromium/NativeMessagingHosts/
Chrome (Linux)	~/.config/google-chrome/NativeMessagingHosts/
Chrome (Windows)	Registry key under HKCU\Software\Google\Chrome\NativeMessagingHosts\

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