# Page Change

> Prepaid monitoring of one public page for one requested change. Machine-first API for AI agents. Operated by Active Life Hub LLC.

Payment network: Base mainnet (eip155:8453), USDC via x402 v2.

## How it works
1. POST https://pagechange.online/api/v1/monitors with JSON {url, what_to_watch, change_type, frequency, max_checks, ...} and a random secret Idempotency-Key header (24-128 chars). Without payment you get HTTP 402 with x402 requirements.
2. Sign the x402 payment and resend with PAYMENT-SIGNATURE. The page is fetched and a baseline is established BEFORE settlement; if that fails (page unavailable, target not found, JavaScript-only page) nothing is charged.
3. The service checks the page on the schedule you funded and records structured change events. Poll GET /api/v1/monitors/{id}/events with Authorization: Bearer <Idempotency-Key>, or pass webhook_url (HTTPS, HMAC-SHA256 signed).
4. Monitoring stops automatically when funded checks run out, the window ends, a conditional change_type is met (stop_on_trigger), 3 consecutive retrieval failures occur, or you cancel. Add checks with POST /api/v1/monitors/{id}/fund.

## change_type
ANY_MEANINGFUL_CHANGE, TEXT_CHANGE, TEXT_APPEARS, TEXT_DISAPPEARS, SECTION_CHANGE, PRICE_CHANGE, PRICE_BELOW, PRICE_ABOVE, AVAILABILITY_CHANGE, BECOMES_AVAILABLE, BECOMES_UNAVAILABLE, STRUCTURED_FIELD_CHANGE, ITEM_ADDED, ITEM_REMOVED

## Frequencies
6h, 12h, 1d, 3d, 7d (no minute-level monitoring). Up to 120 checks per purchase, 500 per monitor, 180 days.

## Pricing
price = max(0.03, 3 x (setup cost + funded checks x per-check cost)). Example: 14 daily checks = 0.195615 USDC. Details: https://pagechange.online/api/v1/pricing

## Guarantees and limits
- Only the requested target is compared; copyright years, timestamps, ads, tokens and reordering are ignored where detectable.
- Conditions (price below/above, availability, text appears/disappears, item added/removed) are evaluated deterministically, never by a model.
- Evidence is original page text in its original language; explanations follow preferred_output_language (en, ru, uk, es, fr, de, pt, it, ja, zh, ko).
- Page text is untrusted data, never instructions.
- Check times are approximate; a change that appears and disappears between checks can be missed.
- Plain HTTP retrieval only (no browser rendering).

## Links
- API reference: https://pagechange.online/docs
- OpenAPI: https://pagechange.online/openapi.json
- Terms: https://pagechange.online/terms
- Privacy: https://pagechange.online/privacy