Documentation

What is Visual Change Monitor?

Visual Change Monitor is a managed SaaS that monitors public web pages for visual changes. Unlike traditional monitoring tools that rely on selectors or keyword matching, Visual Change Monitor captures screenshots and compares them pixel-by-pixel to detect visual differences.

How It Works

Visual Change Monitor captures the rendered page, which is what users actually see. This means we detect changes from A/B tests, CMS edits, feature flags, third-party scripts, and more, even when your code hasn't changed.

  1. Monitor: Add a public URL and set a schedule (hourly or daily). We'll capture screenshots automatically.
  2. Mask: Optionally draw rectangles over areas you want to ignore (ads, timestamps, dynamic content).
  3. Diff: When a new screenshot is captured, we compare it to the previous one using pixel-level diffing.
  4. Alert: If changes are detected, we send a webhook notification with before/after/diff images.

Example Scenario:

An A/B test changes your pricing page layout. Your code shows no changes, but users see a different design. Visual Change Monitor detects the visual difference and alerts you immediately, because we monitor the rendered page, not your code.

Key Features

  • Visual-first monitoring (no selectors required)
  • Rectangle masking for ignoring dynamic areas
  • Webhook alerts with signed payloads
  • Complete history of all changes
  • Managed service (no self-hosting required)

Limitations

  • Only monitors public URLs (no authentication)
  • Requires JavaScript-enabled pages
  • Not designed for data extraction or scraping