PostHog Webhooks & Events
Overview
PostHog sends webhooks via its CDP (Customer Data Platform) Destinations feature. You configure a Destination that fires when matching events are captured, sending an HTTP POST to your endpoint. This skill covers webhook destination setup, receiving and processing webhook payloads, querying events via the API, and using HogQL for custom event analysis.
Prerequisites
- PostHog project with personal API key (
phx_...)
- HTTPS endpoint to receive webhooks
- Events being captured in PostHog
Instructions
Step 1: Create a Webhook Destination via API
set -euo pipefail
curl -X POST "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID/pipeline_destinations/" \
-H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"name": "Signup Notifications",
"description": "Send webhook when user signs up",
"config": {
"url": "https://your-app.com/webhooks/posthog",
"method": "POST",
"headers": {
"X-Webhook-Secret": "your-webhook-secret"
},
"body": {
"event": "{event}",
"distinct_id": "{distinct_id}",
"person": "{person}",
"properties": "{properties}",
"timestamp": "{timestamp}"
}
},
"filters": {
"events": [
{"id": "user_signed_up", "type": "events"},
{"id": "subscription_started", "type": "events"}
]
}
}'
Step 2: Receive and Process Webhooks
import { NextResponse } from 'next/server';
import crypto from 'crypto';
const WEBHOOK_SECRET = process.env.POSTHOG_WEBHOOK_SECRET!;
function verifySignature(payload: string, signature: string): boolean {
const expected = crypto.createHmac('sha256', WEBHOOK_SECRET)
.update(payload)
.digest('hex');
return crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected));
}
interface PostHogWebhookPayload {
event: string;
distinct_id: string;
properties: Record<string, any>;
person: {
properties: Record<string, any>;
};
timestamp: string;
}
export async function POST(request: Request) {
const body = await request.text();
const signature = request.headers.get('x-webhook-secret') || '';
if (WEBHOOK_SECRET && signature !== WEBHOOK_SECRET) {
return NextResponse.json({ error: 'Invalid signature' }, { status: 401 });
}
const payload: PostHogWebhookPayload = JSON.parse(body);
switch (payload.event) {
case 'user_signed_up':
await onUserSignup(payload);
break;
case 'subscription_started':
await onSubscriptionStarted(payload);
break;
case 'subscription_canceled':
await onSubscriptionCanceled(payload);
break;
default:
console.log(`Unhandled PostHog event: ${payload.event}`);
}
return NextResponse.json({ received: true });
}
async function onUserSignup(payload: PostHogWebhookPayload) {
const { distinct_id, properties, person } = payload;
console.log(`New signup: ${distinct_id}`);
await fetch('https://api.hubspot.com/contacts/v1/contact/', {
method: 'POST',
headers: { Authorization: `Bearer ${process.env.HUBSPOT_KEY}` },
body: JSON.stringify({
properties: [
{ property: 'email', value: person.properties.email },
{ property: 'posthog_id', value: distinct_id },
],
}),
});
await fetch(process.env.SLACK_WEBHOOK_URL!, {
method: 'POST',
body: JSON.stringify({
text: `New signup: ${person.properties.email || distinct_id} (${properties.source || 'unknown'})`,
}),
});
}
async function onSubscriptionStarted(payload: PostHogWebhookPayload) {
console.log(`New subscription: ${payload.distinct_id}, plan: ${payload.properties.plan}`);
}
async function onSubscriptionCanceled(payload: PostHogWebhookPayload) {
console.log(`Cancellation: ${payload.distinct_id}`);
}
Step 3: Query Events via the API
set -euo pipefail
curl "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID/events/?event=user_signed_up&limit=10&orderBy=-timestamp" \
-H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY" | \
jq '.results[] | {
distinct_id,
event,
timestamp,
properties: (.properties | {source, plan, referrer: ."$referrer"})
}'
curl "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID/events/?distinct_id=user-123&limit=20" \
-H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY" | \
jq '.results[] | {event, timestamp}'
Step 4: Query Events with HogQL
async function queryPostHog(hogql: string) {
const response = await fetch(
`https://app.posthog.com/api/projects/${process.env.POSTHOG_PROJECT_ID}/query/`,
{
method: 'POST',
headers: {
'Content-Type': 'application/json',
Authorization: `Bearer ${process.env.POSTHOG_PERSONAL_API_KEY}`,
},
body: JSON.stringify({
query: { kind: 'HogQLQuery', query: hogql },
}),
}
);
return response.json();
}
const funnelData = await queryPostHog(`
SELECT
properties.$referrer AS referrer,
count() AS signups,
uniq(distinct_id) AS unique_users
FROM events
WHERE event = 'user_signed_up'
AND timestamp > now() - interval 30 day
GROUP BY referrer
ORDER BY signups DESC
LIMIT 20
`);
const adoptionData = await queryPostHog(`
SELECT
person.properties.plan AS plan,
properties.feature_name AS feature,
count() AS usage_count,
uniq(distinct_id) AS unique_users
FROM events
WHERE event = 'feature_used'
AND timestamp > now() - interval 7 day
GROUP BY plan, feature
ORDER BY usage_count DESC
LIMIT 50
`);
Step 5: Set Up Slack Webhook Destination (UI)
PostHog has built-in Slack integration via Data Pipelines > Destinations:
- Go to Data Pipelines > Destinations > New Destination
- Select "Slack" or "Webhook"
- Configure event filters (which events trigger the notification)
- Set the webhook URL and message template
- Test with a sample event
Error Handling
| Issue | Cause | Solution |
|---|
| Webhook not firing | No matching destination filter | Check event name matches filter exactly |
| Duplicate webhooks | Event matches multiple destinations | Narrow destination filters |
| Webhook timeout | Handler too slow | Acknowledge with 200 immediately, process async |
| HogQL query timeout | Unfiltered table scan | Add timestamp > filter and LIMIT |
| 429 on events API | Too many queries | Cache results, reduce polling frequency |
Output
- Webhook destination configured for specific events
- Express/Next.js webhook handler with event routing
- Event queries via REST API and HogQL
- Slack/CRM integration on user lifecycle events
Resources
Next Steps
For deployment setup, see posthog-deploy-integration.
