API Debugger Overlay

API Debugger Overlay is a Chrome Manifest V3 extension that captures fetch and XMLHttpRequest traffic from the current page and shows a live in-page debugging overlay. It is built for frontend engineers, fullstack developers, and QA engineers who want quick API visibility without opening DevTools.

Current Status

The project has the core extension scaffold and several PRD features implemented:

• MV3 Chrome extension setup with content script, injected page script, background service worker, popup, and side panel.
• Real-time request feed for fetch and XHR calls.
• Request metadata: method, URL, status, duration, request size, response size, timestamp, request body, response body, and TTFB where available.
• Duplicate request detection using FNV-1a fingerprinting over normalized method, URL, and body.
• Configurable capture settings, latency threshold, payload threshold, overlay position, and API key field from the popup.
• In-page overlay with live session metrics, status badges, slow request badges, duplicate badges, and a Canvas latency sparkline.
• Lazy JSON response viewer with tree expansion, search, copy JSON, and basic AI suggestion UI.
• Side panel with session dashboard, latency chart, dependency graph view, and request replay view.
• Request replay routed back through the original tab context so cookies/session state are preserved.
• AI suggestion requests routed through the background service worker with sanitization and rate limiting.
• Anthropic API key stored encrypted in chrome.storage.local, with migration from earlier plaintext storage.
• Focused Vitest unit coverage for encrypted settings storage and AI prompt sanitization.

Still pending from the PRD:

• Broader automated coverage for request interception, session metrics, replay, export, and E2E extension flows.
• Per-node JSON path copy.
• CI/CD workflow and Chrome Web Store packaging polish.

Project Structure

src/
  injected/      Page-context script that wraps fetch and XMLHttpRequest
  content/       Content script and React overlay mounted in Shadow DOM
  background/    MV3 service worker for session storage and message routing
  popup/         Extension popup settings UI
  sidepanel/     Session dashboard, dependency map, and replay UI
  shared/        Shared settings and TypeScript types
tests/           Reserved for unit and E2E tests
manifest.json    Chrome extension manifest
vite.config.ts   Vite + CRX build config

Requirements

• Node.js 20+
• pnpm
• Chrome 114+ for chrome.sidePanel

Setup

Install dependencies:

pnpm install

Run the development build:

pnpm dev

Create a production build:

pnpm build

Run linting:

pnpm lint

Run tests:

pnpm test --run
pnpm test:e2e

The unit suite uses Vitest. The E2E suite uses Playwright to load the built extension into Chromium and exercise a local test page.

Loading In Chrome

1. Run pnpm build.
2. Open chrome://extensions.
3. Enable Developer mode.
4. Click Load unpacked.
5. Select the generated dist directory.
6. Open a website that performs API calls and activate the extension.

How It Works

The content script runs at document_start and injects src/injected/index.js into the page context. The injected script wraps window.fetch and XMLHttpRequest methods, captures completed request details, and sends those details back through window.postMessage.

The content script forwards captured events to the service worker and renders the overlay inside a Shadow DOM root so host page styles do not leak into the UI. The service worker keeps an in-memory per-tab session and broadcasts updates to the overlay and side panel.

Request replay is initiated from the overlay or side panel, sent through the service worker, and executed back in the original tab context using the page's native fetch.

Privacy

Captured request data is processed locally in memory for the current tab session. Session data is cleared when the tab navigates or closes.

The popup stores regular settings in chrome.storage.sync and stores the optional API key encrypted in chrome.storage.local.

No request data is sent to external services unless the user explicitly clicks Ask AI. In that case, sanitized request context is sent from the background service worker to api.anthropic.com, subject to a local rate limit.

PRD Alignment

The implementation is currently closest to phases 1-3 of the PRD, with partial phase 4 work:

• Phase 1: scaffold, injection, fetch/XHR interception, bridge, and basic overlay are implemented.
• Phase 2: duplicate detection, latency alerts, payload sizing, and JSON viewer are partially to mostly implemented.
• Phase 3: session metrics, Canvas chart, and popup settings are implemented. Regular settings now use sync storage; the API key remains local.
• Phase 4: side panel, replay flow, dependency graph rendering, and heuristic dependency inference are implemented.
• Phase 5: AI integration and HTML export are implemented.
• Phase 6: focused unit tests exist; broader test coverage, polish, CI/CD, and release materials are pending.

Scripts

Command	Description
pnpm dev	Start Vite development server
pnpm build	Build the Chrome extension into dist
pnpm preview	Preview the Vite build
pnpm lint	Run ESLint over src
pnpm test	Run Vitest unit tests in tests/unit
pnpm test:e2e	Run Playwright extension E2E tests
pnpm test:all	Run unit and E2E tests

CI

GitHub Actions runs linting, unit tests, production build, and Playwright E2E tests on pushes and pull requests to main. E2E failures upload Playwright reports and traces as artifacts.

License

MIT. See LICENSE.