Langfuse webhooks events

Langfuse Webhooks & Events

Overview

Configure Langfuse webhooks to receive notifications on prompt version changes. Langfuse supports webhook events for prompt lifecycle: Created, Updated (labels/tags changed), and Deleted. Use webhooks to trigger CI/CD pipelines, sync prompts to external systems, or notify teams via Slack.

Prerequisites

• Langfuse Cloud or self-hosted instance
• HTTPS endpoint to receive webhook POST requests
• Webhook secret for HMAC signature verification

Instructions

Step 1: Create Webhook Endpoint

// app/api/webhooks/langfuse/route.ts (Next.js App Router)
import { NextRequest, NextResponse } from "next/server";
import crypto from "crypto";

const WEBHOOK_SECRET = process.env.LANGFUSE_WEBHOOK_SECRET!;

interface LangfuseWebhookEvent {
  event: "prompt.created" | "prompt.updated" | "prompt.deleted";
  timestamp: string;
  data: {
    promptName: string;
    promptVersion: number;
    labels?: string[];
    projectId: string;
    [key: string]: any;
  };
}

// Verify HMAC SHA-256 signature
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)
  );
}

export async function POST(request: NextRequest) {
  const payload = await request.text();
  const signature = request.headers.get("x-langfuse-signature");

  // Verify webhook authenticity
  if (!signature || !verifySignature(payload, signature)) {
    return NextResponse.json({ error: "Invalid signature" }, { status: 401 });
  }

  const event: LangfuseWebhookEvent = JSON.parse(payload);
  console.log(`Langfuse webhook: ${event.event} - ${event.data.promptName}`);

  switch (event.event) {
    case "prompt.created":
      await handlePromptCreated(event.data);
      break;
    case "prompt.updated":
      await handlePromptUpdated(event.data);
      break;
    case "prompt.deleted":
      await handlePromptDeleted(event.data);
      break;
  }

  return NextResponse.json({ received: true });
}

async function handlePromptCreated(data: LangfuseWebhookEvent["data"]) {
  // Trigger CI/CD pipeline for new prompt version
  if (data.labels?.includes("production")) {
    await triggerPromptDeployPipeline(data.promptName, data.promptVersion);
  }

  await notifySlack({
    text: `New prompt version: *${data.promptName}* v${data.promptVersion}`,
    labels: data.labels,
  });
}

async function handlePromptUpdated(data: LangfuseWebhookEvent["data"]) {
  // Label change -- check if promoted to production
  if (data.labels?.includes("production")) {
    await notifySlack({
      text: `Prompt *${data.promptName}* v${data.promptVersion} promoted to production`,
    });
  }
}

async function handlePromptDeleted(data: LangfuseWebhookEvent["data"]) {
  await notifySlack({
    text: `Prompt *${data.promptName}* v${data.promptVersion} deleted`,
    level: "warning",
  });
}

Step 2: Configure Webhook in Langfuse

1. Navigate to Prompts > Create Automation > Webhook
2. Enter your endpoint URL: https://your-domain.com/api/webhooks/langfuse
3. Select events to watch: Created, Updated, Deleted
4. Optionally filter to specific prompts
5. Generate and save the webhook secret
6. Click Test to verify connectivity

Step 3: Slack Integration

// lib/slack-notify.ts

async function notifySlack(params: {
  text: string;
  labels?: string[];
  level?: "info" | "warning";
}) {
  const color = params.level === "warning" ? "#ff9800" : "#36a64f";

  await fetch(process.env.SLACK_WEBHOOK_URL!, {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({
      attachments: [
        {
          color,
          blocks: [
            {
              type: "section",
              text: { type: "mrkdwn", text: params.text },
            },
            ...(params.labels
              ? [
                  {
                    type: "context",
                    elements: [
                      {
                        type: "mrkdwn",
                        text: `Labels: ${params.labels.join(", ")}`,
                      },
                    ],
                  },
                ]
              : []),
          ],
        },
      ],
    }),
  });
}

Step 4: Trigger CI/CD Pipeline on Prompt Changes

// Trigger GitHub Actions workflow when production prompt changes
async function triggerPromptDeployPipeline(promptName: string, version: number) {
  await fetch(
    `https://api.github.com/repos/${process.env.GITHUB_REPO}/dispatches`,
    {
      method: "POST",
      headers: {
        Authorization: `Bearer ${process.env.GITHUB_TOKEN}`,
        "Content-Type": "application/json",
      },
      body: JSON.stringify({
        event_type: "prompt-updated",
        client_payload: { promptName, version },
      }),
    }
  );
}

# .github/workflows/prompt-deploy.yml
name: Deploy Updated Prompt
on:
  repository_dispatch:
    types: [prompt-updated]

jobs:
  test-and-deploy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with: { node-version: "20", cache: "npm" }
      - run: npm ci

      - name: Test updated prompt
        env:
          LANGFUSE_PUBLIC_KEY: ${{ secrets.LANGFUSE_PUBLIC_KEY }}
          LANGFUSE_SECRET_KEY: ${{ secrets.LANGFUSE_SECRET_KEY }}
          OPENAI_API_KEY: ${{ secrets.OPENAI_API_KEY }}
        run: |
          echo "Testing prompt: ${{ github.event.client_payload.promptName }}"
          npx vitest run tests/ai/prompt-quality.test.ts

Step 5: Webhook Reliability with Retry Queue

// For production: queue webhook processing to return 200 fast
import { Queue, Worker } from "bullmq";

const webhookQueue = new Queue("langfuse-webhooks", {
  connection: { host: process.env.REDIS_HOST },
});

// In webhook handler -- enqueue and respond immediately
export async function POST(request: NextRequest) {
  const payload = await request.text();
  // ... verify signature ...

  await webhookQueue.add("process", JSON.parse(payload), {
    attempts: 3,
    backoff: { type: "exponential", delay: 1000 },
  });

  return NextResponse.json({ received: true }); // Return fast
}

// Worker processes asynchronously
const worker = new Worker(
  "langfuse-webhooks",
  async (job) => {
    const event = job.data as LangfuseWebhookEvent;
    // Process event...
  },
  { connection: { host: process.env.REDIS_HOST } }
);

Webhook Event Reference

Event	Trigger	Use Case
prompt.created	New prompt version added	Run regression tests, notify team
prompt.updated	Labels or tags changed	Detect production promotions
prompt.deleted	Prompt version removed	Alert on accidental deletion

Error Handling

Issue	Cause	Solution
Invalid signature (401)	Wrong webhook secret	Re-copy secret from Langfuse settings
Missed events	Handler threw error	Queue events, return 200 immediately
Duplicate processing	Retry without idempotency	Dedupe by event + timestamp + promptName
Webhook timeout	Slow handler	Enqueue and process async

Resources

• Langfuse Webhooks
• Prompt Version Webhooks Changelog
• GitHub Integration