Add REST API Tester Chrome Extension with Manifest V3

[Copilot]

Implements a lightweight Chrome extension for testing REST API endpoints directly from the browser using Manifest V3, vanilla JavaScript, Chrome Storage API, and Fetch API.

Extension Structure

• manifest.json - MV3 config with storage/host permissions, service worker, popup action
• background.js - Service worker managing popup window lifecycle
• popup.html/css/js - Request builder UI with response viewer

Features

• HTTP methods: GET, POST, PUT, PATCH, DELETE
• Body formats: JSON, Form Data (toggle)
• Custom headers with add/remove
• Formatted JSON responses with syntax highlighting
• Status codes with color-coded badges + response timing
• Endpoint persistence via Chrome Storage API

Security

• XSS prevention: textContent for plain text responses, HTML escaping in JSON formatter
• Try-catch for malformed JSON response handling

// Safe response handling
if (isFormattedJson) {
  responseContent.innerHTML = responseText; // Pre-escaped in formatJSON
} else {
  responseContent.textContent = responseText; // Prevents XSS
}

Original prompt

Lightweight browser extension that lets allows me devs to test REST API endpoints directly from the browser. Tech Stack: 1. Manifest V3 Chrome extension 2. Vanilla Javascript (no frameworks) Chrome Storage API for storing endpoints. Fetch API for HTTP requests. Architecture: Manifest.json - Extension configuration 2. Background.js - Service worker for window management. 3. popup.html/css/js - Main UI with request builder and response viewer. Opens as a persistent window.

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