Send a Webhook to Trello: Transform & Forward Any Payload

You have a service that fires webhooks — a form, a payment provider, a CI pipeline, a monitoring tool — and you want each event to create a card in Trello. The problem: the Trello API won't accept the raw webhook. It expects its own JSON shape and authentication, and the payload your source sends never matches.

Webhook Relay sits in the middle. It receives the incoming webhook at a stable public URL, transforms the payload into the format Trello expects, and delivers it — no glue server, no Lambda, no maintenance.

How it works

1. Your source service POSTs its webhook to a Webhook Relay endpoint.
2. A transformation function parses the payload and builds a Trello API request.
3. Webhook Relay forwards it to Trello, and the record is created.

Step 1: Get your Trello credentials

You need a Trello API key and token (trello.com/app-key), and the list ID to add cards to.

Step 2: Create a Webhook Relay output to the Trello API

Create a bucket with a public input, then add an output pointing at the Trello API:

• Output destination: https://api.trello.com/1/cards?key=KEY&token=TOKEN&idList=LIST_ID — Trello takes the key, token and target list as query parameters, not headers.
• Headers: Content-Type: application/json

Step 3: Add a transformation function

Attach a function that reshapes the incoming webhook. Trello's create-card endpoint takes the key, token and idList as query parameters and the card name/desc in the body.

-- incoming payload is in r.RequestBody
local body = json.decode(r.RequestBody)

local card = {
  name = body.title or "Card from webhook",
  desc = body.message or r.RequestBody
}

r:SetRequestBody(json.encode(card))

Step 4: Point your source at the URL and test

Configure your source service's webhook to point at the Webhook Relay public URL. Trigger an event — or replay one from the Webhook Bin — and the record appears in Trello within seconds. If the API rejects the request, the Webhook Relay logs show Trello's exact error so you can fix the mapping.

Going further

• Fan out: send the same event to Jira or Discord at the same time with multiple destinations.
• Filter: use forwarding rules so only the events you care about reach Trello.
• Inspect first: see the raw payload in the Webhook Bin before writing the mapping.

Get started

Create a free Webhook Relay account and turn any webhook into Trello records — no servers to run. New to webhooks? Start with what is a webhook and how to transform webhooks.