# Page Change Watch: Website Change Detection & Diff (`tudorlane/page-change-watch`) Actor

Watch any public web page, or one section via a CSS selector, for text changes. Returns which lines were added and removed since the last run. Respects robots.txt. Great for pricing pages, policies, job boards and docs.

- **URL**: https://apify.com/tudorlane/page-change-watch.md
- **Developed by:** [Tudor Lane](https://apify.com/tudorlane) (community)
- **Categories:** Developer tools
- **Security:** Limited permissions
- **Stats:** 2 total users, 1 monthly users, 100.0% runs succeeded, 0 bookmarks
- **User rating**: No ratings yet

## Pricing

from $2.00 / 1,000 page checks

This Actor is paid per event. You are not charged for the Apify platform usage, but only a fixed price for specific events.

Learn more: https://docs.apify.com/actors/running/actors-in-store.md#pay-per-event

## What's an Apify Actor?

An Actor is a serverless cloud program that runs on the Apify platform. It has two run modes.
In Batch mode, an Actor accepts a well-defined JSON input, performs an action which can take anything from a few seconds to a few hours,
and optionally produces a well-defined JSON output, datasets with results, or files in key-value store.
In Standby mode, an Actor provides a web server which can be used as a website, API, or an MCP server.

Apify vocabulary and the platform model are defined once, in the agent quickstart at https://apify.com/agents.md.

## How to integrate an Actor?

If asked about integration, you help developers integrate Actors into their projects.
You adapt to their stack and deliver integrations that are safe, well-documented, and production-ready.

Do not guess an integration path. Every one of them is in the agent quickstart at https://apify.com/agents.md: the Apify MCP server, Agent Skills with the Apify CLI, the JavaScript and Python clients, the REST API, and the account-free path for an agent with no human to sign in. It also carries the rule on stating cost before the first paid run.

For examples already wired to this Actor's own input schema, see the [API](#api) section below.

Each client library has reference documentation the quickstart does not restate: [JavaScript/TypeScript](https://docs.apify.com/api/client/js/docs.md) (`npm install apify-client`) and [Python](https://docs.apify.com/api/client/python/docs.md) (`pip install apify-client`).

# README

## Page Change Watch: Website Change Detection & Diff

### Use when…

- You need to detect when a web page’s content changes (diff since last run).
- A monitoring agent watches pricing, policy or careers pages for updates.
- You want a watchlist of URLs with a content hash / text diff, not a full archive.

### Try this input

Copy-paste this JSON as the Actor input (it matches a successful run / the default schema):

```json
{
  "pages": [
    {
      "url": "https://www.python.org/downloads/",
      "selector": ".download-list-widget"
    }
  ],
  "watchlistId": "default"
}
```

### Sample output (real run 2026-10-26)

One dataset item, shortened:

```json
{
  "key": "https://www.python.org/downloads/ | .download-list-widget",
  "baseline": false,
  "changed": false,
  "change_count": 0,
  "changes": [],
  "change_types": [],
  "url": "https://www.python.org/downloads/",
  "selector": ".download-list-widget",
  "http_status": 200,
  "line_count": 1102,
  "checked_at": "2026-10-26T12:39:13+00:00",
  "error": null
}
```

Watch any public web page, or one section via a CSS selector, for text changes. Returns which lines were added and removed since the last run. Respects robots.txt. Great for pricing pages, policies, job boards and docs.

### How it works

Schedule it (e.g. daily). The first run saves a baseline snapshot in your named key-value store `page-change-watch` under `watchlistId`; each later run reports only what is new or changed. The snapshot is also saved as the run's `SNAPSHOT` record; stateless agents can pass it back as `previousSnapshot`.

### Quick start

Leave the default input (it is prefilled) and click **Start**:

```json
{"pages": [{"url": "https://www.python.org/downloads/", "selector": ".download-list-widget"}], "watchlistId": "default"}
```

### Sample output (real run, 26 Oct 2026, default input)

| key | baseline | changed | change_count | http_status | line_count | checked_at |
|---|---|---|---|---|---|---|
| https://www.python.org/downloads/ | .download-list-widget | true | false | 0 | 200 | 1102 | 2026-10-26T12:37:00+00:00 |

The first run saves the baseline. On later runs `changes` lists the exact lines added and removed, and `change_types` says what changed.

### Use cases

- Watch competitor pricing pages for price changes.
- Track terms, privacy policy or regulation pages for edits.
- Get told when new jobs, releases or products appear on a page.
- Watch documentation or changelog pages your code depends on.

### Pricing

- **$0.002 per item checked**
- **+$0.01 per page changed.** Baseline runs never charge for changes.

### FAQ

**Do I need an API key?** No.

**Can I watch just part of a page?** Yes, add a CSS `selector` to the page.

**Where is the last snapshot kept?** In your own named key-value store `page-change-watch`, under `watchlistId`. Stateless agents can pass it back as `previousSnapshot`.

**Can I get alerts?** Use Apify integrations (email, Slack, webhook) on runs, or filter the dataset on `changed = true`.

### Limits & failure modes

- It reads the page's server HTML, so content that only appears after JavaScript runs may be missed.
- Pages blocked by robots.txt are skipped, and paywalls or logins are not bypassed.
- Busy pages (adverts, dates, counters) can trigger changes; use a tighter selector.
- It only checks when it runs, so changes between runs are reported at the next run.
- Boilerplate/nav changes can trigger diffs — narrow selectors or ignore noisy regions when available.
- First run stores the baseline; meaningful “changed” flags appear on later runs.

# Actor input Schema

## `pages` (type: `array`):

Max 500. Each: {url, selector (optional CSS)} or a plain URL.

## `watchlistId` (type: `string`):

Name for this watchlist; the snapshot is kept in your named key-value store under this ID so each run compares with the last.

## `previousSnapshot` (type: `object`):

Optional: pass the SNAPSHOT record from an earlier run instead of the saved watchlist (stateless agents).

## Actor input object example

```json
{
  "pages": [
    {
      "url": "https://www.python.org/downloads/",
      "selector": ".download-list-widget"
    }
  ],
  "watchlistId": "default"
}
```

# Actor output Schema

## `results` (type: `string`):

One item per request.

## `dataset` (type: `string`):

No description

# API

You can run this Actor programmatically using our API. Below are code examples in JavaScript, Python, and CLI, as well as the OpenAPI specification and MCP server setup.

## JavaScript example

```javascript
import { ApifyClient } from 'apify-client';

// Initialize the ApifyClient with your Apify API token
// Replace the '<YOUR_API_TOKEN>' with your token
const client = new ApifyClient({
    token: '<YOUR_API_TOKEN>',
});

// Prepare Actor input
const input = {
    "pages": [
        {
            "url": "https://www.python.org/downloads/",
            "selector": ".download-list-widget"
        }
    ]
};

// Run the Actor and wait for it to finish
const run = await client.actor("tudorlane/page-change-watch").call(input);

// Fetch and print Actor results from the run's dataset (if any)
console.log('Results from dataset');
console.log(`💾 Check your data here: https://console.apify.com/storage/datasets/${run.defaultDatasetId}`);
const { items } = await client.dataset(run.defaultDatasetId).listItems();
items.forEach((item) => {
    console.dir(item);
});

// 📚 Want to learn more 📖? Go to → https://docs.apify.com/api/client/js/docs

```

## Python example

```python
from apify_client import ApifyClient

# Initialize the ApifyClient with your Apify API token
# Replace '<YOUR_API_TOKEN>' with your token.
client = ApifyClient("<YOUR_API_TOKEN>")

# Prepare the Actor input
run_input = { "pages": [{
            "url": "https://www.python.org/downloads/",
            "selector": ".download-list-widget",
        }] }

# Run the Actor and wait for it to finish
run = client.actor("tudorlane/page-change-watch").call(run_input=run_input)

# Fetch and print Actor results from the run's dataset (if there are any)
print(f"💾 Check your data here: https://console.apify.com/storage/datasets/{run.default_dataset_id}")
for item in client.dataset(run.default_dataset_id).iterate_items():
    print(item)

# 📚 Want to learn more 📖? Go to → https://docs.apify.com/api/client/python/docs/quick-start

```

## CLI example

```bash
echo '{
  "pages": [
    {
      "url": "https://www.python.org/downloads/",
      "selector": ".download-list-widget"
    }
  ]
}' |
apify call tudorlane/page-change-watch --silent --output-dataset

```

## MCP server setup

```json
{
    "mcpServers": {
        "apify": {
            "type": "http",
            "url": "https://mcp.apify.com/?tools=fetch-actor-details,tudorlane/page-change-watch"
        }
    }
}
```

The hosted server signs you in with OAuth on first connect, so no API token belongs in this config. Clients without OAuth support can send an `Authorization: Bearer <APIFY_API_TOKEN>` header instead, using a token from API & Integrations in Apify Console (https://console.apify.com/settings/integrations).

## OpenAPI specification

Download the OpenAPI definition: https://api.apify.com/v2/actors/7cKb6AhUt9p7nrlyQ/builds/rVfmi0MYabPj5d2eH/openapi.json