Replicate Webhooks

When to Use This Skill

• Setting up Replicate webhook handlers
• Debugging signature verification failures
• Understanding Replicate event types and payloads
• Handling prediction lifecycle events (start, output, logs, completed)

Essential Code (USE THIS)

Express Webhook Handler

const express = require('express');
const crypto = require('crypto');

const app = express();

// CRITICAL: Use express.raw() for webhook endpoint - Replicate needs raw body
app.post('/webhooks/replicate',
  express.raw({ type: 'application/json' }),
  async (req, res) => {
    // Get webhook headers
    const webhookId = req.headers['webhook-id'];
    const webhookTimestamp = req.headers['webhook-timestamp'];
    const webhookSignature = req.headers['webhook-signature'];

    // Verify we have required headers
    if (!webhookId || !webhookTimestamp || !webhookSignature) {
      return res.status(400).json({ error: 'Missing required webhook headers' });
    }

    // Manual signature verification (recommended approach)
    const secret = process.env.REPLICATE_WEBHOOK_SECRET; // whsec_xxxxx from Replicate
    const signedContent = `${webhookId}.${webhookTimestamp}.${req.body}`;

    try {
      // Extract base64 secret after 'whsec_' prefix
      const secretBytes = Buffer.from(secret.split('_')[1], 'base64');
      const expectedSignature = crypto
        .createHmac('sha256', secretBytes)
        .update(signedContent)
        .digest('base64');

      // Replicate can send multiple signatures, check each one
      const signatures = webhookSignature.split(' ').map(sig => {
        const parts = sig.split(',');
        return parts.length > 1 ? parts[1] : sig;
      });

      const isValid = signatures.some(sig => {
        try {
          return crypto.timingSafeEqual(
            Buffer.from(sig),
            Buffer.from(expectedSignature)
          );
        } catch {
          return false; // Different lengths = invalid
        }
      });

      if (!isValid) {
        return res.status(400).json({ error: 'Invalid signature' });
      }

      // Check timestamp to prevent replay attacks (5-minute window)
      const timestamp = parseInt(webhookTimestamp, 10);
      const currentTime = Math.floor(Date.now() / 1000);
      if (currentTime - timestamp > 300) {
        return res.status(400).json({ error: 'Timestamp too old' });
      }
    } catch (err) {
      console.error('Signature verification error:', err);
      return res.status(400).json({ error: 'Invalid signature' });
    }

    // Parse the verified webhook body
    const prediction = JSON.parse(req.body.toString());

    // Handle the prediction based on its status
    console.log('Prediction webhook received:', {
      id: prediction.id,
      status: prediction.status,
      version: prediction.version
    });

    switch (prediction.status) {
      case 'starting':
        console.log('Prediction starting:', prediction.id);
        break;
      case 'processing':
        console.log('Prediction processing:', prediction.id);
        if (prediction.logs) {
          console.log('Logs:', prediction.logs);
        }
        break;
      case 'succeeded':
        console.log('Prediction completed successfully:', prediction.id);
        console.log('Output:', prediction.output);
        break;
      case 'failed':
        console.log('Prediction failed:', prediction.id);
        console.log('Error:', prediction.error);
        break;
      case 'canceled':
        console.log('Prediction canceled:', prediction.id);
        break;
      default:
        console.log('Unknown status:', prediction.status);
    }

    res.status(200).json({ received: true });
  }
);

Common Prediction Statuses

Environment Variables

# Your webhook signing secret from Replicate
REPLICATE_WEBHOOK_SECRET=whsec_your_secret_here

Local Development

For local webhook testing, install the Hookdeck CLI:

# Install via npm
npm install -g hookdeck-cli

# Or via Homebrew
brew install hookdeck/hookdeck/hookdeck

Then start the tunnel:

hookdeck listen 3000 --path /webhooks/replicate

No account required. Provides local tunnel + web UI for inspecting requests.

Reference Materials

• What are Replicate webhooks — Event types and payload structure
• Setting up webhooks — Dashboard configuration and signing secret
• Signature verification — Verification algorithm and common issues

Resources for Implementation

Framework Examples

• Express implementation — Node.js with Express
• Next.js implementation — React framework with API routes
• FastAPI implementation — Python async framework

Documentation

• Official Replicate webhook docs
• Webhook setup guide
• Webhook verification guide

Recommended: webhook-handler-patterns

Enhance your webhook implementation with these patterns:

• Handler sequence
• Idempotency
• Error handling
• Retry logic

Related Skills

• stripe-webhooks - Stripe payment webhooks
• github-webhooks - GitHub repository events
• shopify-webhooks - Shopify store events
• clerk-webhooks - Clerk authentication events
• webhook-handler-patterns - Idempotency, error handling, retry logic
• hookdeck-event-gateway - Webhook infrastructure that replaces your queue — guaranteed delivery, automatic retries, replay, rate limiting, and observability for your webhook handlers