monitor.page webhook

{
  "success": true,
  "type": "monitor.page",
  "id": "whd_5c1e9a2b7d3f4e6a8b0c2d4e6f8a1b3c",
  "created_at": "2026-10-12T06:01:02.481Z",
  "monitor_id": "mon_3f9a1c2b7d4e4f6a8b0c1d2e3f4a5b6c",
  "monitor_name": "Competitor pricing",
  "check_id": "chk_8e2d4f6a1b3c4d5e6f7a8b9c0d1e2f3a",
  "data": {
    "target_id": "tgt_8d1e0f2a3b4c5d6e",
    "url": "https://example.com/pricing",
    "status": "changed",
    "status_code": 200,
    "error": null,
    "title": "Pricing — Example",
    "previous_check_id": "chk_51b0c2d3e4f5a6b7c8d9e0f1a2b3c4d5",
    "is_meaningful": true,
    "judgment": {
      "meaningful": true,
      "confidence": "high",
      "reason": "The Starter plan's price went from $19 to $24 a month.",
      "meaningful_changes": [
        {
          "type": "changed",
          "before": "$19/mo",
          "after": "$24/mo",
          "reason": "A plan price changed."
        }
      ]
    },
    "diff": {
      "fields": {
        "plans[0].price": {
          "previous": "$19/mo",
          "current": "$24/mo",
          "change": "changed"
        }
      },
      "changed_fields": 1
    },
    "snapshot": {
      "json": {
        "plans": [
          {
            "name": "Starter",
            "price": "$24/mo",
            "features": [
              "3 seats",
              "Email support"
            ]
          },
          {
            "name": "Pro",
            "price": "$49/mo",
            "features": [
              "Unlimited seats",
              "SSO"
            ]
          }
        ]
      }
    }
  },
  "metadata": {
    "env": "production"
  }
}

WEBHOOK

monitor.page

{
  "success": true,
  "type": "monitor.page",
  "id": "whd_5c1e9a2b7d3f4e6a8b0c2d4e6f8a1b3c",
  "created_at": "2026-10-12T06:01:02.481Z",
  "monitor_id": "mon_3f9a1c2b7d4e4f6a8b0c1d2e3f4a5b6c",
  "monitor_name": "Competitor pricing",
  "check_id": "chk_8e2d4f6a1b3c4d5e6f7a8b9c0d1e2f3a",
  "data": {
    "target_id": "tgt_8d1e0f2a3b4c5d6e",
    "url": "https://example.com/pricing",
    "status": "changed",
    "status_code": 200,
    "error": null,
    "title": "Pricing — Example",
    "previous_check_id": "chk_51b0c2d3e4f5a6b7c8d9e0f1a2b3c4d5",
    "is_meaningful": true,
    "judgment": {
      "meaningful": true,
      "confidence": "high",
      "reason": "The Starter plan's price went from $19 to $24 a month.",
      "meaningful_changes": [
        {
          "type": "changed",
          "before": "$19/mo",
          "after": "$24/mo",
          "reason": "A plan price changed."
        }
      ]
    },
    "diff": {
      "fields": {
        "plans[0].price": {
          "previous": "$19/mo",
          "current": "$24/mo",
          "change": "changed"
        }
      },
      "changed_fields": 1
    },
    "snapshot": {
      "json": {
        "plans": [
          {
            "name": "Starter",
            "price": "$24/mo",
            "features": [
              "3 seats",
              "Email support"
            ]
          },
          {
            "name": "Pro",
            "price": "$49/mo",
            "features": [
              "Unlimited seats",
              "SSO"
            ]
          }
        ]
      }
    }
  },
  "metadata": {
    "env": "production"
  }
}

When it is sent

One event per page that, in a check:

changed since the previous check,
is new — a page that appeared since the monitor’s first check,
was removed — it answers 404 or 410, or a complete crawl no longer finds it,
or started failing. A page that stays down sends one event, not one per check.

Two things are never sent: the first check’s baseline, where every page is new by definition, and changes the judge ruled not meaningful. Both are still recorded on the check. data is the same page object GET /monitor/{id}/checks/{checkId} returns — status, diff, judgment and, in json mode, the current extraction.

Responding

Answer with any 2xx within 10 seconds. Anything else — a timeout, a 4xx or 5xx, a redirect — is retried after 1, 5 and 15 minutes, then marked failed. Do slow work after you respond. Retries carry the same id, also sent as X-Prefetch-Delivery. Store the ids you have processed and skip repeats.

Verify the signature

Every request carries an X-Prefetch-Signature header:

X-Prefetch-Signature: t=1760248862,v1=5f2b8c1e...

v1 is the hex HMAC-SHA256 of <t>.<raw request body>, keyed with the monitor’s webhook.secret. The timestamp is signed too, so a captured request cannot be replayed with a fresh header — reject anything older than five minutes. Verify against the raw body, before any JSON parsing: re-serialising changes the bytes and breaks the signature.

import crypto from "node:crypto";
import express from "express";

const app = express();

app.post("/hooks/prefetch", express.raw({ type: "application/json" }), (req, res) => {
  const header = req.get("X-Prefetch-Signature") || "";
  const { t, v1 } = Object.fromEntries(header.split(",").map((kv) => kv.split("=")));

  const fresh = Math.abs(Date.now() / 1000 - Number(t)) <= 300;
  const expected = crypto
    .createHmac("sha256", process.env.PREFETCH_WEBHOOK_SECRET)
    .update(`${t}.${req.body}`)
    .digest();
  const given = Buffer.from(v1 || "", "hex");

  if (!fresh || given.length !== expected.length || !crypto.timingSafeEqual(given, expected)) {
    return res.status(401).send("invalid signature");
  }

  const event = JSON.parse(req.body);
  res.sendStatus(200); // acknowledge first, then do the work
  handle(event);
});

import hashlib, hmac, os, time
from flask import Flask, request, abort

app = Flask(__name__)

@app.post("/hooks/prefetch")
def prefetch_webhook():
    header = request.headers.get("X-Prefetch-Signature", "")
    parts = dict(kv.split("=", 1) for kv in header.split(",") if "=" in kv)
    t, v1 = parts.get("t", "0"), parts.get("v1", "")

    expected = hmac.new(
        os.environ["PREFETCH_WEBHOOK_SECRET"].encode(),
        f"{t}.".encode() + request.get_data(),
        hashlib.sha256,
    ).hexdigest()

    if abs(time.time() - int(t)) > 300 or not hmac.compare_digest(v1, expected):
        abort(401)

    event = request.get_json()
    # ... handle the event
    return "", 200

The secret is in the monitor’s webhook.secret. To change it, update the monitor with "rotate_secret": true — see PATCH /monitor/{id}.

Headers

Header	Value
`X-Prefetch-Event`	`monitor.page`
`X-Prefetch-Delivery`	The delivery id — the same as `id` in the body
`X-Prefetch-Signature`	`t=<unix seconds>,v1=<hex HMAC-SHA256>`
`User-Agent`	`Prefetch-Webhooks/1.0`

Any headers you set on the monitor’s webhook are sent as well.

monitor.check.completed

One event per check, with its counts.

POST /monitor

Configure the webhook and the goal.

Authorizations

X-API-Key

string

header

required

Your Prefetch API key. Obtain one from the dashboard.

Headers

X-Prefetch-Event

string

required

The event type.

X-Prefetch-Delivery

string

required

The delivery id — the same as id in the body, and stable across retries.

X-Prefetch-Signature

string

required

t=<unix seconds>,v1=<hex>, where hex is HMAC-SHA256 of "<t>.<raw body>" keyed with the monitor's webhook.secret.

Example:

"t=1760248862,v1=5f2b8c..."

Body

application/json

success

boolean

string

Delivery id, also sent as X-Prefetch-Delivery. Stable across retries — use it to de-duplicate.

Example:

"whd_5c1e9a2b7d3f4e6a8b0c2d4e6f8a1b3c"

created_at

string<date-time>

monitor_id

string

monitor_name

string

check_id

string

metadata

object

The metadata you set on the webhook.

type

enum<string>

Available options:

monitor.page

data

object

Show child attributes

Response

200

Answer any 2xx within 10 seconds. Anything else, or no answer, is retried after 1, 5 and 15 minutes.

Overview

Discovery

Endpoints

Web extraction

Batch

Logo CDN

Monitoring

When it is sent

Responding

Verify the signature

Headers

monitor.check.completed

POST /monitor

Authorizations

Headers

Body

Response

​When it is sent

​Responding

​Verify the signature

​Headers

​Related

monitor.check.completed

POST /monitor

Authorizations

Headers

Body

Response

When it is sent

Responding

Verify the signature

Headers

Related