Angular Render Scan

Angular Render Scan is a visual debugging overlay for Angular change detection. It shows which components update, how often they update, and which checks are slow or wasted.

Live Demo | npm

What it shows

• Component render outlines and heatmap colors.
• Slow render and budget violation alerts.
• Change detection trigger labels such as zone:click, signal:write, and router:navigation.
• OnPush candidates, referentially unstable inputs, and suspected Zone pollution.
• A copyable AI performance prompt for slow/error components.
• Session export JSON for deeper debugging.

Install

npm install angular-render-scan

Angular Render Scan expects Angular 9+.

Setup with the CLI

npx angular-render-scan-cli init

The CLI supports Angular CLI and Nx workspaces. It looks for angular.json, workspace.json, nx.json, or project.json, finds your main.ts or app.config.ts, and adds provideAngularRenderScan().

npx angular-render-scan-cli init --dry-run
npx angular-render-scan-cli init --script-tag
npx angular-render-scan-cli --help

Manual Setup

Add the provider to your Angular bootstrap config.

import { bootstrapApplication } from '@angular/platform-browser';
import { provideAngularRenderScan } from 'angular-render-scan';
import { AppComponent } from './app/app.component';

bootstrapApplication(AppComponent, {
  providers: [
    provideAngularRenderScan({
      enabled: true,
      animationSpeed: 'fast'
    })
  ]
});

For script-tag usage:

<script src="https://unpkg.com/angular-render-scan/dist/auto.global.js"></script>

Provider mode is recommended for Angular component-level instrumentation.

Common Options

provideAngularRenderScan({
  enabled: true,
  showToolbar: true,
  showFPS: true,
  animationSpeed: 'fast',
  maxLabelCount: 20,
  maxRecordedCycles: 30,
  showCopyPrompt: true,
  promptContext: 'Angular app using signals and OnPush components',
  log: false
});

Useful options:

• enabled: turns scanning on or off.
• showToolbar: shows the floating toolbar.
• animationSpeed: 'fast', 'slow', or 'off'.
• showFPS: shows FPS in the toolbar.
• log: prints cycle summaries to the console.
• include / exclude: limits which components are tracked.
• minDurationMs / minRenderCount: filters low-signal entries.
• maxRecordedCycles: controls how much history is included in copied prompts.
• promptContext: adds app-specific context to copied prompts.
• dangerouslyForceRunInProduction: allows scanner runtime outside Angular dev mode.

Runtime API

import {
  copyAIPrompt,
  getAIPrompt,
  getCdGraph,
  getOnPushCandidates,
  getOptions,
  getReferentialInstability,
  getZonePollutionEvents,
  scan,
  setOptions,
  stop
} from 'angular-render-scan';

scan();
setOptions({ enabled: false });
setOptions({ enabled: true, log: true });

console.log(getOptions());
console.log(getAIPrompt());
await copyAIPrompt();

console.log(getOnPushCandidates(40));
console.log(getReferentialInstability(1));
console.log(getZonePollutionEvents());
console.log(getCdGraph());

stop();

Toolbar

The toolbar shows render count, FPS, latest cycle time, slowest component, trigger source, OnPush candidates, Zone pollution events, alerts, and copy/export actions.

Useful shortcuts:

Shortcut	Action
Alt+Shift+S	Toggle scanner
Alt+Shift+D	Toggle Details Mode
Alt+Shift+C	Copy AI performance prompt
Alt+Shift+X	Clear stats
Alt+Shift+T	Toggle toolbar
Escape	Close open panels

Details and AI Prompt

Enable Details in the toolbar, hover a captured component, then click it to pin a recommendation panel. The panel shows timing, render count, reason, selector, changed inputs, recent cycles, and local Angular recommendations.

Use Copy Slow Issues Prompt to copy a focused prompt for an AI coding assistant. It includes recent cycle history, thresholds, and slow/error component evidence without copying DOM nodes, component instances, or source code.

Playwright Audit

import { test, expect } from '@playwright/test';
import { startRenderAudit } from 'angular-render-scan';

test('no render regression', async ({ page }) => {
  await page.goto('/');

  const audit = await startRenderAudit(page);
  await page.click('button.expensive-operation');
  const report = await audit.stop();

  expect(await report.maxDurationFor('ProductCardComponent')).toBeLessThan(16.7);
  expect(await report.wastedRenderPercentage()).toBeLessThan(20);
  expect(await report.budgetViolations()).toHaveLength(0);
});

Production Behavior

Angular Render Scan is intended for development and demo debugging. Provider mode checks Angular isDevMode() and does not run in production unless explicitly enabled.

provideAngularRenderScan({
  dangerouslyForceRunInProduction: true
});

Use that option carefully. The scanner adds runtime instrumentation, DOM reads, canvas work, and debug behavior.

Demo

Hosted demo:

https://edisonaugusthy.github.io/angular-render-scan/

Local demo:

npm install
npm run dev

Open http://127.0.0.1:4200/.

Development

npm run test
npm run build
npm run test:e2e

Release

Release runs automatically on pushes to main. The workflow bumps the package version, publishes angular-render-scan and angular-render-scan-cli to npm, and creates a GitHub release.

Configure NPM_TOKEN or npm trusted publishing for both packages before publishing.