Webhook overview - LeadFast

LeadFast sends a signed POST when a relevant public Reddit post matches your product. Delivery is at least once.

The setup prompt below is the whole integration. Paste it into your coding agent and it will build and test the endpoint with you.

Endpoint requirements

One public HTTPS URL on port 443.
Respond with any 2xx status within 10 seconds.
Redirects are not followed.
The same body and LeadFast-Delivery value may arrive more than once: deduplicate.

Headers

Header	Value
`LeadFast-Event`	`webhook.test`, `reddit.post.matched`, or `product.understanding.updated`
`LeadFast-Delivery`	Stable UUID for deduplicating retries
`LeadFast-Signature`	`t=UNIX_SECONDS,v1=HEX_HMAC`

Request shape

curl --request POST 'https://your-domain.example/leadfast' \
  --header 'Content-Type: application/json' \
  --header 'LeadFast-Event: webhook.test' \
  --header 'LeadFast-Delivery: 00000000-0000-4000-8000-000000000000' \
  --header 'LeadFast-Signature: t=TIMESTAMP,v1=HMAC_SHA256' \
  --data '{"event":"webhook.test","version":1,"test":true,"sent_at":"2026-08-29T18:03:00.000Z"}'

Send a real test from the app before relying on an endpoint: a destination is only active after a successful test.

Verify signatures

HMAC-SHA256, raw bytes and the five-minute window.

Event payloads

Every field of every event.