Website Change Detection
Get an alert when a web page changes in a way that matters: text that must be there disappears, an error message appears, the page shrinks or grows sharply, or its HTML layout breaks.
Three ways to catch a changed page
Most pages change all the time: timestamps, prices, rotating content. Alerting on every byte is noise. Webalert gives you three checks, each tuned to a different kind of change, and you can combine them on one monitor.
- Keyword alerts
- Require a word or phrase to be present, such as "Add to cart" or your footer copyright, or require one to be absent, such as "Out of stock", "Database error", or a spam keyword. Case-sensitive matching is optional. A failed keyword check counts as the page being down, so it opens an incident and alerts like an outage.
- Starter
- Content change alerts
- Compares each response's size against the median of your recent successful checks and alerts when it moves by more than your threshold. The default is 20% against the last 10 checks; you can set 1–100% and 5–50 checks. Small day-to-day variation is filtered out, so a gutted page or an injected block stands out.
- Starter
- DOM structure alerts
- Hashes the page's HTML layout, not its text, and alerts when the structure changes: a section disappears, a template breaks, or new markup is injected. Images, icons, dynamic state classes, and repeated list items are normalised away, so new blog posts or product listings do not trigger it.
- Business
How webpage change alerts work
1
Add the page
Create an HTTP monitor for the URL and switch on the change checks you want.
2
Pick the cadence
Keyword checks run with every uptime check. Content and structure checks run every 5 minutes to every hour, with a notification cooldown so one change alerts once.
3
Get the alert
Alerts go to the same channels as your outage alerts: email, Slack, SMS, and the rest of your configured notification channels.
What teams use it for
- Defacement and injected spam: a hacked page usually changes size or structure, or starts containing words it never should. Pair it with SEO cloaking detection to catch content shown only to Googlebot.
- A "200 OK" that is actually broken: an empty template, a maintenance page, or an error rendered with a success status. A keyword check catches what a status code cannot.
- Bad deploys and CMS edits: a missing checkout button, a removed pricing table, or a layout that broke after a plugin update.
- Pages you depend on but do not own: a partner's terms page, a supplier's status text, or a competitor's pricing page.
Webalert alerts you that a page changed and how much; it does not store screenshots or show a word-by-word diff. If you need visual comparison, read visual regression monitoring for how that approach differs.
Frequently asked questions
- How do I get an alert when a web page changes?
- Add the URL as an HTTP monitor in Webalert and turn on a change check. Use a keyword check for specific text, content change alerts for large changes in page size, or DOM structure alerts for layout changes. Alerts arrive on your normal notification channels.
- Will it alert me every time a timestamp or price changes?
- No. Content change alerts compare against the median of recent checks and only fire past your threshold, and DOM structure alerts ignore text entirely. If you want to know about one specific value, use a keyword check for that value.
- How often are pages checked for changes?
- Keyword checks run with every uptime check, up to every minute on paid plans. Content and DOM structure checks run on their own schedule, from every 5 minutes to every hour.
- Which plans include change detection?
- Keyword alerts and content change alerts are on the Starter and Business plans. DOM structure alerts are on the Business plan. See pricing for details.
- Can I monitor a page I don't own?
- Yes, as long as the page is publicly reachable. Webalert fetches it like a normal visitor, so pages behind a login are not covered unless you monitor an endpoint that accepts your own headers or token.
Related Features
Know when your pages change
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Related Articles
Content Change Detection: Meaningful Alerts
Text, DOM, selector, and visual diffs, and how to cut noise from dynamic content.
Response Body Validation
Why a 200 OK can still be a broken page, and how keyword checks catch it.
Website Security Monitoring
Detect defacement, malware injection, and other unwanted changes fast.