Webhooks

A price alert watches one provider's price for one model and POSTs a signed JSON body to your endpoint when that price changes.

Create an alert

1. Open the dashboard.
2. Choose a provider, then a model.
3. Enter your endpoint URL. It must be https.
4. Copy the signing secret. It is shown on creation and stays readable on the alert's row.

Limit: 10 alerts per account. Alerts are created in the dashboard only. No endpoint creates, lists or deletes one, and /api/v1 stays read-only.

Events

One event type, price.changed, in three kinds:

Watched fields: input, output, cache_read, cache_write, reasoning, context, unit. A rename, a new tag, or a re-read that returns the same number is not a change and sends nothing.

Sources are polled every five minutes. A move large enough to look like a parsing error is held until a second reading confirms it, so a webhook arrives once, after the price is published, and never twice for the same change.

The request

POST /your/endpoint HTTP/1.1
content-type: application/json
user-agent: indextkn-webhooks/1

Payload

{
  "id": "0f2b6c48-1f7e-4a02-9a1e-8b0c0f0f0f0f",
  "type": "price.changed",
  "kind": "changed",
  "created_at": "2026-08-31T12:04:07.000Z",
  "alert": {
    "id": "3a9f2c10-7d61-4f5e-9a2b-1c2d3e4f5a6b",
    "provider": "anthropic",
    "model": "anthropic/claude-opus-4.5"
  },
  "model": {
    "id": "anthropic/claude-opus-4.5",
    "lab": "anthropic",
    "name": "Claude Opus 4.5",
    "modality": "text"
  },
  "provider": "anthropic",
  "provider_model_id": "claude-opus-4-5",
  "changed": ["input", "cache_read"],
  "old": {
    "name": "Claude Opus 4.5",
    "input": 5,
    "output": 25,
    "cache_read": 0.5,
    "cache_write": 6.25,
    "reasoning": null,
    "unit": "1M_tokens",
    "context": 200000,
    "max_output": 64000,
    "status": "accurate"
  },
  "new": {
    "name": "Claude Opus 4.5",
    "input": 4.5,
    "output": 25,
    "cache_read": 0.45,
    "cache_write": 6.25,
    "reasoning": null,
    "unit": "1M_tokens",
    "context": 200000,
    "max_output": 64000,
    "status": "checking"
  },
  "source_url": "https://www.anthropic.com/pricing",
  "observed_at": "2026-08-31T12:04:07.000Z"
}

old and new

The same shape on both sides. old is every value held before the change, new is every value held after it, and changed names the difference. Prices are USD per unit. There is no history in the payload: the two states either side of this change, nothing older.

Confidence

old.status and new.status carry the accuracy status each price held when it was published, the same values /api/v1 puts on an offer. The old price keeps the confidence it was published with, so a delivery says both how far the number you were using was trusted and how far its replacement is.

Status is not one of the watched fields: a status moving on its own does not send a webhook. Read new.status before acting on a price automatically. suspicious and failed mean the number has not been confirmed.

Verify the signature

Compute the HMAC over the raw request bytes. Re-serializing parsed JSON changes the bytes and will not match.

X-Indextkn-Signature: t=1756642, v1=8a1f...c2

  signed_payload = "<t>" + "." + "<raw request body>"
  v1             = hex(hmac_sha256(alert_secret, signed_payload))

1. Read t and v1 from the header.
2. Reject the request if t is more than five minutes old.
3. Compute hmac_sha256(secret, t + "." + rawBody) as hex.
4. Compare it to v1 in constant time.

import { createHmac, timingSafeEqual } from "node:crypto";

// rawBody must be the exact bytes we sent, before any JSON parsing.
export function verify(rawBody, signature, secret) {
  const parts = Object.fromEntries(
    signature.split(",").map((p) => p.split("=")),
  );
  // Reject anything older than five minutes: that is what the timestamp is for.
  if (Math.abs(Date.now() / 1000 - Number(parts.t)) > 300) return false;

  const expected = createHmac("sha256", secret)
    .update(`${parts.t}.${rawBody}`)
    .digest("hex");

  return (
    expected.length === parts.v1.length &&
    timingSafeEqual(Buffer.from(expected), Buffer.from(parts.v1))
  );
}

Responses and retries

Endpoint requirements

• https on port 443, no credentials in the URL.
• A public host. A URL that resolves to a private, loopback or link-local address is refused, and the check is repeated immediately before every send.
• Respond within 10 seconds. Do the work after you respond.
• Treat X-Indextkn-Delivery as an idempotency key. A retry repeats it.

Failures

After 10 consecutive failed deliveries the alert is disabled and stops firing. The dashboard shows it as disabled with the last error. Resuming it there clears the counter and starts delivery again. A single successful delivery also resets the counter.

Delivery log

Every attempt is recorded against your account: the time, the listing, the fields that changed, the URL it went to, the exact body sent, and the status your endpoint returned. The dashboard shows the last 30 days under Webhook log. Deleting an alert deletes its log with it.