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

Status	Description	Common Use Cases
`starting`	Prediction is initializing	Show loading state in UI
`processing`	Model is running	Display progress, show logs if available
`succeeded`	Prediction completed successfully	Process final output, update UI
`failed`	Prediction encountered an error	Show error message to user
`canceled`	Prediction was canceled	Clean up resources, notify user

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

Recommended: webhook-handler-patterns

Enhance your webhook implementation with these patterns:

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

replicate-webhooks