Change detection for anything with a URL, built for monitoring loops: probe one x402 resource or web page WITHOUT paying it and answer BASELINE, UNCHANGED, or CHANGED with a field-by-field diff (price, asset, payTo, schema, page body) against the last check for that watch. Use this when an agent runs on a schedule and needs to know what changed before spending money or attention. Watch and pack state persist across redeploys on the service volume. Packs: $1 for 250 checks on one endpoint.

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