Step 1: Get your URL ready

• make sure that you’ll be able to prove ownership of the site that hosts your web app.
• bookmark this page: https://chrome.google.com/webstore/developer/dashboard

Step 2: Create a manifest.json file

• create a new directory on your local computer, create a text file named manifest.json and copy the following code into it, changing the italicized text to reflect your app feature.

• {
    "manifest_version": 2,
    "name": "Your App Name",
    "description": "This extension displays a form for an realtor to import MLS data, analyze the data imported, and return a PDF form for download.",
    "version": "1.0",
  
    "browser_action": {
      "default_icon": "icon.png",
      "default_popup": "popup.html",
      "default_title": "Your App Title"
    },
    "permissions": [
      "activeTab",
      "https://ajax.googleapis.com/"
    ]
  }
  

Step 3: Create images

Your app requires icon 128px x 128px and tiny icon of 19px x 19px

Step 4: Get the popup.js file

Download the initial popup.js file here

Step 5: Load the Extension for testing and packing

1. Type chrome://extensions in browser (or open up the Chrome menu by clicking the icon to the far right of the Omnibox: and select Extensions under the Tools menu to get to the same place).
2. Make sure that the Developer mode checkbox in the top right-hand corner is checked.
3. Click Load unpacked extension… to pop up a file-selection dialog.
4. Navigate to the directory in which your extension files live, and select it.

This is just a basic how to start to build a Chrome Extension. If you need more powerful API to build complex extension, please visit this page https://developer.chrome.com/extensions/api_index