Integration directory

Google Forms × Slack — webhook spec

The delivery layer of the integration, incoming-webhook contract, payload shape, retry semantics, idempotency. Read this when you want to know exactly what bytes hit Slack and what happens when they don't.

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Slack incoming webhook (no app install)
JSON payload, mrkdwn or Block Kit
Auto-retry with exponential backoff

Spec

The webhook contract

Google FormsSlackIntegration

Trigger

RouteForms POST to https://hooks.slack.com/services/…

Action

Content-Type: application/json. Body: mrkdwn message or Block Kit JSON.

Fields available

text, icon_emoji, username, blocks, attachments

Payload

Example rendered payload

POST https://hooks.slack.com/services/T0/B0/XXX
Content-Type: application/json

{
  "icon_emoji": ":inbox_tray:",
  "username": "RouteForms",
  "text": "*New lead*. Acme Corp\n*Name:* Jane Doe\n*Email:* jane@acme.com"
}

Slack responds ok (200) on success. Any non-2xx triggers retry or failure logging per the rules below.

Reliability

Retry and idempotency semantics

Retry trigger: HTTP 5xx, HTTP 429
Backoff: 2s → 6s → 18s → 54s → cap
No retry on: 4xx (except 429)
Idempotency key: Google Forms response ID
Failure alert: After 3 consecutive failures (paid)
Audit: Delivery log, payload + status + retries

Errors

What Slack will tell you when it rejects

invalid_payload: JSON didn't parse or required field missing. Often a stray brace from template editing. Decode via /tools/slack-webhook-error-decoder.
channel_not_found: channel deleted or archived. Re-create webhook bound to the new channel.
no_service / 404, webhook URL revoked or regenerated by the workspace admin. New URL needed.
rate_limited(429), too many posts to the same workspace in a short window. RouteForms retries; if it persists, you're likely fanning out to too many channels per minute.

Setup

Three steps

1
Create the Slack incoming webhook
Slack → Settings & administration → Manage apps → Incoming Webhooks. Pick the channel, copy the URL.
2
Paste the webhook URL into RouteForms
On the form's settings tab in the RouteForms dashboard. Stored encrypted; displayed masked thereafter.
3
Install the Apps Script and submit a test response
Verify the delivery log shows DELIVERED with HTTP 200 OK. Done.

FAQ

Frequently asked questions

What does Slack expect at the webhook URL?▾

A POST with Content-Type application/json and a JSON body. The minimum body is {"text": "hello"}. For rich messages, the body is either Slack mrkdwn (text + extras like icon_emoji, username) or a Block Kit blocks array. RouteForms renders the message from your template and POSTs the resulting JSON; you see the exact bytes in the delivery log.

How does RouteForms know to retry?▾

On a 5xx response or a 429 (rate limit), the delivery is retried with exponential backoff — 2s, 6s, 18s, 54s, then a final cap. Permanent failures (404 channel not found, 400 invalid payload) aren't retried; they're logged with the error and surface in the failure-alert email after 3 consecutive failures (paid plans).

What stops duplicate posts on retry?▾

The Google Forms response ID. Every submission carries a unique response ID, and RouteForms tracks it through the whole pipeline. If a retry races with the original (rare; usually only on partial network failures), the second delivery sees the response ID is already DELIVERED and short-circuits. The Slack channel sees exactly one post per real submission.

Can I use a Block Kit payload instead of plain text?▾

Yes. The template editor accepts either mrkdwn or Block Kit. For Block Kit, paste the blocks array; RouteForms renders {{placeholders}} inside it and POSTs the resulting JSON. The Slack Block Kit payload generator (linked below) is the fastest way to build the JSON visually.

What does the delivery log capture about each webhook POST?▾

The Google Forms response ID, the matched routing rule (if any), the rendered payload JSON, the HTTP status code Slack returned, the Slack response body, the timestamp, the number of retries, and the final status (DELIVERED / FAILED / SKIPPED). Click a row to see the full payload, useful when the Slack rendering doesn't match expectations.