Website Change Monitor & Diff API

Monitor public websites and JSON endpoints for meaningful changes without paying the browser/screenshot cost on every check. Run one URL or hundreds at once, save persistent baselines between runs, suppress predictable noise, and receive a structured record describing exactly what changed.

Use an Apify Schedule to turn the Actor into a recurring website monitor, or call it from the API, Make, Zapier, n8n, or another Actor.

What this Actor monitors

• Text changes — strips scripts, styles, SVG, comments, and HTML markup before comparison.
• HTML changes — compares normalized returned HTML when markup changes matter.
• Prices and selected values — regex mode compares only extracted matches, so unrelated page updates do not trigger a change.
• JSON/API fields — compares stable JSON with object-key ordering normalized, optionally using an RFC 6901 JSON Pointer such as /product/price.
• HTTP status and availability — detects status changes, request failures, repeated failures, and recovery.
• Redirect destinations — detects when the final URL changes.

Every run writes one structured dataset row per page check. Filter changed = true to isolate only changes.

Why use it

Many website monitors are optimized for screenshots and browser interaction. This Actor is deliberately optimized for fast, repeatable HTTP checks and automation pipelines:

• Up to 500 monitors in one run.
• No CSS selector required for ordinary text monitoring.
• Regex extraction for prices, inventory labels, versions, dates, counts, IDs, or any value you can match.
• JSON Pointer support for APIs.
• Persistent state across scheduled runs.
• Ignore regexes for timestamps, rotating IDs, counters, and other known dynamic content.
• Conditional ETag and Last-Modified requests; HTTP 304 responses reuse the previous body instead of downloading it again.
• Structured current/previous previews and focused diff snippets.
• Predictable pay-per-check billing.
• Limited-permission compatible. The Actor does not need access to unrelated account data.
• Private, loopback, link-local, and reserved destinations are blocked to reduce SSRF risk.

Quick start

The default input monitors https://example.com/ in text mode. The first run creates a baseline, so baseline = true and changed = false. Run the same input again to compare the current page with that baseline.

{
  "monitors": [
    {
      "id": "example-homepage",
      "url": "https://example.com/",
      "mode": "text"
    }
  ]
}

Monitor a competitor price

Use regex mode to compare only the value you care about. When a capture group is present, the Actor compares capture group 1.

{
  "stateNamespace": "competitor-prices",
  "monitors": [
    {
      "id": "competitor-pro-plan",
      "url": "https://example.com/pricing",
      "mode": "regex",
      "extractRegex": "Pro Plan\\s*\\$([0-9,.]+)",
      "regexFlags": "gi"
    }
  ]
}

Ignore timestamps and other noise

Known dynamic text can be removed before hashing and comparison.

{
  "monitors": [
    {
      "id": "policy-page",
      "url": "https://example.com/policy",
      "mode": "text",
      "ignorePatterns": [
        "Last updated: \\d{4}-\\d{2}-\\d{2} \\d{2}:\\d{2}",
        "request-id=[A-F0-9-]+"
      ]
    }
  ]
}

Use globalIgnorePatterns when the same dynamic pattern appears on every monitored page.

Monitor one JSON API field

jsonPointer follows RFC 6901. Leave it empty to compare the full JSON payload. Object key order is normalized automatically.

{
  "stateNamespace": "api-watch",
  "monitors": [
    {
      "id": "inventory-count",
      "url": "https://api.example.com/product/123",
      "mode": "json",
      "jsonPointer": "/inventory/available"
    }
  ]
}

Monitor uptime or a status page

Status mode intentionally ignores response-body changes and watches the request/status/redirect state.

{
  "monitors": [
    {
      "id": "vendor-health",
      "url": "https://status.example.com/",
      "mode": "status"
    }
  ]
}

Output

Each checked monitor produces one dataset item. Important fields include:

Field	Meaning
baseline	true when no prior state existed for this monitor configuration.
changed	Whether the current observation differs from the prior observation.
changeTypes	Reasons such as content, status, redirect-target, request-failed, recovered, or error-type.
statusCode / previousStatusCode	Current and previous effective HTTP status.
currentPreview / previousPreview	Bounded previews of compared content.
diff	Focused removed/added snippets and an approximate changed-span percentage.
notModified	true when the server returned HTTP 304 and the previous body was reused.
error	Safe error code and message if the request or extraction failed.

Example changed result:

{
  "monitorId": "competitor-pro-plan",
  "url": "https://example.com/pricing",
  "mode": "regex",
  "baseline": false,
  "changed": true,
  "changeTypes": ["content"],
  "requestSucceeded": true,
  "statusCode": 200,
  "previousStatusCode": 200,
  "currentPreview": "[\"12\"]",
  "previousPreview": "[\"10\"]",
  "diff": {
    "removed": "0",
    "added": "2"
  }
}

Persistent baselines and namespaces

The Actor stores comparison state in its own named key-value store (website-change-monitor-diff-api-state-v1). State is isolated by stateNamespace, monitor identity, and monitoring configuration. The Actor-owned state includes the normalized comparison content needed to create future before/after diffs; it is not sent to any third-party service by this Actor.

Use a distinct stateNamespace for separate Apify Tasks that may monitor the same URL. Changing a monitor's URL, comparison mode, extraction regex, JSON Pointer, or normalization configuration automatically establishes a fresh baseline rather than comparing incompatible values.

Set resetBaseline to true when you intentionally want the current values to become new baselines.

Scheduling

For continuous monitoring:

1. Save the input as an Apify Task.
2. Add a Schedule (for example hourly or daily).
3. Use the dataset output directly, or connect the run/dataset to your preferred automation workflow.
4. Filter for changed = true when the downstream workflow should act only on changes.

A page check is the billable unit, including a baseline check or a check that reports an HTTP/network failure. The result is still useful because it records the observed state.

Reliability and safety limits

The Actor is built for public HTTP/HTTPS content and includes bounded defaults:

• Request timeout: 20 seconds.
• Retry attempts: 1 for transient network errors and common retryable HTTP statuses.
• Redirects: maximum 5.
• Response body: 1 MB per check by default, configurable up to a hard maximum of 1.5 MB.
• Concurrency: 8 by default, configurable from 1 to 16.
• Monitors per run: maximum 500.

Private, loopback, link-local, reserved, and local-network targets are blocked, including redirects that attempt to reach those destinations.

Limitations

• This release monitors the HTTP response returned by the server. It does not execute page JavaScript or take screenshots.
• Pages whose important content exists only after browser-side rendering, login, clicking, scrolling, or CAPTCHA interaction need a browser-based Actor instead.
• Anti-bot protections may block datacenter requests on some websites.
• Regex extraction is intentionally deterministic and restricted to a conservative safety subset; backreferences, lookarounds, named groups, and potentially unsafe nested quantified groups are rejected.
• Automated monitoring does not grant permission to access content. Follow the target website's terms, applicable law, and reasonable request rates.

Recommended use cases

• Competitor pricing and plan changes.
• Product availability or inventory labels.
• Terms, policy, compliance, and vendor-document changes.
• Documentation and changelog monitoring.
• Career page and announcement monitoring.
• API field changes.
• Status, outage, redirect, and recovery monitoring.
• Landing-page or offer-copy monitoring.

Cost control

This Actor uses pay-per-event pricing with a page-check event. One delivered dataset row equals one page check. Apify also lets you set a maximum charge per run before starting it.

See the Pricing tab on the Actor page for the current per-check price and subscription-tier discounts.