Keystroke Sender

A Chrome Native Messaging host that simulates OS-level keystrokes. Receives text strings from a Chrome extension and types them out as real key presses using pynput.

Works on macOS, Linux, and Windows.

Companion extension: Chrome Form Filler (dpdolkkncejkelemckjmjoaefmgdhepj)

Prerequisites

• Python 3.7+
• pip
• Google Chrome
• Chrome Form Filler extension

Installation

pip install (recommended)

pip install keystroke-sender

Then register the Chrome native messaging host:

keystroke-sender-register YOUR_EXTENSION_ID

To unregister later:

keystroke-sender-register --unregister

Manual install (macOS / Linux)

chmod +x install.sh
./install.sh

Manual install (Windows)

install.bat

The manual installer will:

1. Prompt you for your Chrome extension ID (find it at chrome://extensions)
2. Create the native messaging host manifest in the correct OS location
3. Install the pynput Python dependency

macOS Accessibility Permission

On macOS, you must grant Accessibility permission to your terminal app (or Python) for keystroke simulation to work:

System Preferences > Privacy & Security > Accessibility — add your terminal app (Terminal, iTerm2, etc.).

Usage

From a Chrome extension, send a message to the native host:

chrome.runtime.sendNativeMessage(
  "com.propdream.keystroke_sender",
  { text: "Hello, world!" },
  (response) => {
    console.log(response);
    // { status: "ok", typed: 13 }
  }
);

Message Format

Request:

{
  "text": "string to type",
  "delay": 0.05
}

• text (required): The string to type as OS-level keystrokes.
• delay (optional): Seconds between each keystroke. Default: 0.05.

Response:

{ "status": "ok", "typed": 13 }

or on error:

{ "status": "error", "message": "description" }

Extension Setup

Add "nativeMessaging" to your extension's manifest.json permissions:

{
  "permissions": ["nativeMessaging"]
}

Uninstallation

macOS / Linux

chmod +x uninstall.sh
./uninstall.sh

Windows

uninstall.bat

Security

This app simulates real keystrokes and mouse clicks at the OS level, so it includes several safeguards to prevent misuse:

Chrome Native Messaging isolation — The host process can only be launched by Chrome, and only the extension ID you registered in allowed_origins can send it messages. No network socket is opened; communication is purely via stdin/stdout. An unauthorized extension or external program cannot talk to it.

Idle timeout — The host automatically exits after 1 minute of inactivity. It does not stay running indefinitely.

Rate limiting — A maximum of 100 actions per second is enforced. Bursts beyond this are rejected with an error response.

Input size limits — Messages larger than 1 MB are rejected before parsing. Text payloads longer than 10,000 characters are rejected before typing.

Limit	Default
Idle timeout	60 s (1 min)
Rate limit	100 actions / 1 s
Max message size	1 MB
Max text length	10,000 chars

These constants are defined at the top of src/keystroke_sender/host.py and can be adjusted if needed.

Debugging

• Launch Chrome from the terminal to see native host stderr output
• Use chrome://extensions > Service Worker > Console to see extension-side errors
• Check chrome.runtime.lastError in the sendNativeMessage callback