How to Monitor Any Website for Changes
A comprehensive, step-by-step guide to setting up automated website monitoring. Whether you are tracking prices, competitor pages, or regulatory content, this guide covers everything you need to know.
1. Why Monitor Websites for Changes
The internet is constantly changing. Product pages are updated, prices shift, competitors adjust their strategies, regulations are revised, and content is published -- all without any obligation to notify you. Manually checking websites for changes is not only tedious but unreliable. You will inevitably miss important updates.
Automated website monitoring solves this by continuously checking pages on your behalf and alerting you only when something changes. This turns a reactive process into a proactive one, giving you a competitive advantage in whatever context you are operating.
Competitive Intelligence
Know when competitors change pricing, features, or messaging.
Compliance & Legal
Track regulatory pages and legal documents for policy changes.
Content & SEO
Monitor your own pages for unauthorized changes or regressions.
Price Tracking
Catch flash sales and price drops before they expire.
2. Choosing the Right Monitoring Approach
There are several approaches to website monitoring, each with trade-offs. Understanding these will help you choose the right setup for your specific needs.
Full-Page Monitoring
Monitors the entire visible content of a web page. Best when you want to catch any change -- layout shifts, new sections, text updates, image swaps, etc. This is the simplest approach and works well for pages that do not change frequently. The downside is that it can be noisy on dynamic pages with ads, timestamps, or session-specific content.
Targeted Element Monitoring (CSS Selectors)
Monitors a specific element on the page, identified by a CSS selector. Best when you care about one piece of content -- a price, a status message, a headline, a product description. This approach eliminates noise by ignoring everything else on the page. It is the most common approach for production monitoring.
Visual (Screenshot) Monitoring
Takes periodic screenshots and compares them visually. Best for detecting visual regressions -- layout breaks, styling changes, image replacements, or design updates that would not be caught by text-only monitoring. OnChange overlays the differences so you can see exactly what changed pixel by pixel.
API Response Monitoring
Monitors the raw response from an HTTP endpoint (typically JSON). Best for tracking APIs, data feeds, and machine-readable content. See our dedicated API monitoring guide for details.
3. Setting Up Your OnChange Account
Getting started with OnChange takes less than a minute. Here is how to create your account and prepare for your first monitor.
Visit the signup page
Head to onchange.sairo.app/signup. You can sign up with your email address or use Google OAuth for faster onboarding.
Verify your email
Check your inbox for a verification email and click the confirmation link. This ensures your alerts are delivered to the right address.
Access your dashboard
Once verified, you are taken directly to your monitoring dashboard. The dashboard is where you will create, manage, and review all your monitors.
4. Creating Your First Monitor
With your account ready, it is time to create your first website monitor. This process involves three key decisions: what URL to watch, what content to track, and how often to check.
Click 'New Monitor' in your dashboard
The new monitor form opens with fields for the URL, monitoring type, and configuration options.
Enter the URL you want to monitor
Paste the full URL of the page you want to track. OnChange will load this page in a real browser environment, so JavaScript-rendered content is fully supported. Dynamic single-page applications work just as well as static HTML pages.
Choose your monitoring type
Select between full-page text monitoring, CSS selector targeting, or visual screenshot monitoring. For most use cases, CSS selector targeting provides the best signal-to-noise ratio.
Preview the page
OnChange renders a preview of the target page. If you selected CSS selector targeting, you can use the visual picker to click on the element you want to watch, or manually enter a CSS selector.
Save and activate the monitor
Review your settings and save. OnChange immediately captures the initial baseline snapshot and begins monitoring on your chosen schedule.
5. Using CSS Selectors for Precision
CSS selectors are the most powerful feature in OnChange for reducing noise and focusing on exactly the content that matters. If you have never used CSS selectors before, here is a quick primer.
Common CSS Selector Patterns
.priceSelects elements with the class "price". The most common way to target price elements.#product-titleSelects the element with the ID "product-title". IDs are unique, so this is very precise.[data-price]Selects elements with a "data-price" attribute. Useful for data-driven sites.h1.entry-titleSelects an h1 element with the class "entry-title". Combines tag and class for specificity..product-card:first-child .priceSelects the price inside the first product card. Useful for category pages.Pro Tip: Finding Selectors
The easiest way to find the right CSS selector is to use your browser's developer tools. Right-click on the element you want to track, select "Inspect," and look at the HTML. Note the class names, IDs, and data attributes. You can also use OnChange's built-in visual element picker, which highlights elements as you hover and generates the selector automatically.
6. Choosing Check Intervals
How often OnChange checks for changes depends on your use case. Here are guidelines for common scenarios to help you balance responsiveness with resource usage.
| Use Case | Recommended Interval | Why |
|---|---|---|
| Flash sale monitoring | 10-30 seconds | Sales can start and end within minutes |
| Competitor pricing | 5-15 minutes | Prices change frequently but rarely by the second |
| Product pages | 1-4 hours | Product specs and descriptions change less often |
| Blog / content pages | 4-12 hours | Content publishing follows editorial schedules |
| Legal / policy pages | Daily | Legal updates are infrequent but critical |
7. Configuring Alerts
OnChange supports multiple notification channels so your team gets change alerts wherever they work. You can configure different channels for different monitors, and a single monitor can send alerts to multiple channels simultaneously.
Receive change notifications in your inbox with a summary of what changed and a link to the full diff. Supports individual addresses and distribution lists.
Slack
Send alerts to any Slack channel via incoming webhooks. Rich formatting includes the page title, what changed, and a link to the diff. See our Slack setup guide for details.
Discord
Similar to Slack, Discord webhooks deliver formatted change notifications to any channel. Great for teams that use Discord as their primary communication tool.
Custom Webhooks
Send raw change data to any HTTP endpoint. Use this to integrate with Zapier, Make, PagerDuty, custom dashboards, or any tool that accepts webhook payloads.
For a detailed walkthrough on Slack integration, see our Slack alerts setup guide.
8. Advanced Monitoring Techniques
Ignoring Dynamic Content
Many pages include dynamic elements like timestamps, ad banners, session IDs, or random recommendation widgets. These trigger false change alerts. Use CSS selectors to target only the static content you care about, effectively filtering out all the noise. If you need full-page monitoring, consider using exclude selectors to remove specific dynamic sections.
Handling Authentication
Some pages require authentication to access. OnChange supports custom headers where you can pass authentication tokens, API keys, or session cookies. For API endpoints, you can configure Bearer tokens or basic auth credentials. This allows you to monitor members-only content, internal dashboards, and authenticated API responses.
Using the API for Automation
The OnChange REST API lets you create, update, and manage monitors programmatically. This is useful for teams that need to onboard hundreds of URLs, integrate monitoring into CI/CD pipelines, or build custom dashboards. You can also retrieve change history and diff data via the API for inclusion in reports and analytics.
9. Troubleshooting Common Issues
My monitor shows changes on every check
The page likely contains dynamic content (timestamps, ads, session data). Switch to CSS selector monitoring and target only the stable content you care about.
The page content appears empty
The page may require JavaScript to render. OnChange uses a headless browser by default, but ensure JavaScript rendering is enabled in your monitor settings.
I am not receiving alert notifications
Verify your notification channel configuration. For email, check spam folders. For Slack/Discord, verify the webhook URL is correct and the channel still exists.
The CSS selector is not matching anything
The page structure may have changed since you set up the selector. Open the page in your browser, use developer tools to inspect the current HTML, and update the selector accordingly.
10. Next Steps
Now that you understand the fundamentals of website monitoring, explore these related guides and resources to get even more value from OnChange.
Ready to Start Monitoring?
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