Webhooks Explained for Vibe Coders
The Questions You Need to Ask Your Replit Agent Before Deploying
Who This Guide Is For:
You're building an app in Replit (or other Vibe Coding tools). You need to receive notifications from other services (like Stripe for payments, Twilio for texts, or Mailchimp for email events). You've heard the word "webhook" but you're not exactly sure what it means or how to make sure yours work correctly.
This guide is for you, the vibe coder who wants to build real apps without getting a computer science degree first.
What the Heck is a Webhook?
Simple explanation: A webhook is like a doorbell for your app. When something important happens on another service, they ring your doorbell (send a message to your app) to let you know.
Real-World Examples:
Stripe (Payment Processing):
Someone pays you → Stripe rings your webhook doorbell → "Hey! You just got paid $50!"
Twilio (SMS/Text Messages):
Someone texts your business number → Twilio rings your webhook doorbell → "Hey! You got a text message!"
Mailchimp (Email Marketing):
Someone subscribes to your newsletter → Mailchimp rings your webhook doorbell → "Hey! New subscriber!"
Why you need webhooks: Without webhooks, your app would have to constantly ask these services "Did anything happen yet? Did anything happen yet?" over and over. Webhooks let them tell YOU when something happens.
The Problem with Vibe Coding Webhooks
Here's the thing: asking Replit Agent to "add webhooks for Stripe payments" sounds simple. And the agent WILL add them. But without asking the right questions, you might end up with webhooks that:
Accept fake messages from hackers pretending to be the service e.g. Stripe (security - worst)
Process the same payment twice (money - very bad)
Lose messages when your app goes down (reliability)
Timeout and fail because they take too long to respond (performance)
Crash your app when something unexpected happens (stability)
The good news: If you ask the right questions BEFORE deploying, the Agent will catch all of these.
How to Use This Guide
Your Pre-Deployment Workflow:
Build your feature: "Add Stripe payment webhooks to handle successful payments…or recurring subscription payments"
Ask these questions: Use the questions in this guide (copy-paste them to Replit Agent)
Review the answers: Make sure the agent addressed each concern
Test thoroughly: Use the testing strategies below
Deploy confidently: Your webhooks are production-ready
Important: Don't wait until AFTER deployment to ask these questions. Ask them while you're still building, so the agent can implement solutions properly.
The Questions to Ask Your Replit Agent
Copy these questions and paste them to Replit Agent after it adds webhooks to your app. The agent will either confirm it already handled these, or it will add the necessary code.
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How do you know this message really came from [service]?
What you're checking: The webhook verifies the message is actually from Stripe/Twilio/etc., not from a hacker.Good answer includes:
We verify the signature using the webhook secret
We use stripe.webhooks.constructEvent()
Invalid signatures are rejected immediately with 400 status
Red flag answer:
We accept all incoming webhooks
We trust the message
No mention of signature/secret
Why it matters: Without this, hackers can POST fake "payment succeeded" messages and get free access to your product.
-
Is the webhook endpoint protected from random people hitting it?
What you're checking: Only the external service can access your webhook, not random internet users.
Good answer includes:
The endpoint is public but validates signatures
We use rate limiting to prevent spam
We return 429 Too Many Requests if limit is exceeded
IPs that fail signature checks repeatedly get blocked
Red flag answer:
We process every request that comes in
No rate limiting mentioned
We rely on Stripe's signature check only
Why it matters: Even if you verify signatures, attackers can flood your endpoint with fake requests, wasting your server resources and potentially causing downtime.
-
What if the same message arrives twice?
What you're checking: Duplicate messages don't cause duplicate actions (like charging a customer twice or sending two confirmation emails).
Good answer includes:
We use idempotency - we track processed event IDs
We check if we've already processed this webhook ID
Duplicates are detected and skipped
Red Flag answer:
We process every webhook we receive
We rely on service (e.g. Stripe) not to send duplicates
No mention of storing/checking event IDs
Why it matters: Stripe, for example, WILL send duplicates (due to network issues, retries). Without idempotency, your customer gets charged twice or receives 5 confirmation emails.
Bonus points if the Agent mention:
We use a database transaction to check-and-process atomically
We store event IDs with a TTL/expiry so the table doesn't grow forever…pay attention to this one
-
What if processing fails - will it retry forever?
Good answer includes:
We return a 200 status immediately, then process in the background
Failed processing is logged for manual retry
We have a dead letter queue for permanently failed webhooks
We have alerts when webhooks fail repeatedly
Red flag answer:
We return 500 on errors so Stripe retries
We do all processing before returning 200
No mention of background processing or queue
The nuance beginners miss:
Some think "return 200 always" is the solution. But you need BOTH:
Return 200 quickly (so service like Stripe stops retrying)
Actually process the event reliably (background job + error handling)
Why this matters: If your webhook takes too long or fails, services like Stripe will keep retrying (sometimes up to 3 days). You need a strategy to handle failures without breaking your app.
The Pattern:
Receive webhook → validate signature
Save event to database (quick)
Return 200 immediately
Process event in background job
If background fails → alert + manual retry option
-
What if my app is down when the message arrives?
What you're checking: You have a plan to recover missed webhooks.
Good answer includes:
Most services will retry automatically for several hours or days
We can manually replay webhooks from the service's dashboard
We log when webhooks are missed so we can investigate
Red Flag answer:
We just hope the app doesn't go down
We don't have monitoring for uptime
No awareness of retry behavior
Real scenario: Your Replit app crashes at 2 AM. A customer makes a payment at 2:15 AM. Stripe sends the webhook, but your app is down. Stripe will retry multiple times over the next 3 days. When your app comes back up, it will receive the webhook.
Side note: Free Replit apps may "sleep" after inactivity. A webhook hitting a sleeping app will wake it up, but there's a delay. For production webhooks, use Replit Deployments (always-on) or ensure your app stays awake.
Know your service: Different services have different retry policies:Stripe: Retries for 3 days
Twilio: Retries for 24 hours
(Check your service's docs!)
-
What events are we listening for?
What you're checking: You know exactly which events your webhook processes.
Good answer includes: A specific list of event types.
Example for Stripe:
payment_intent.succeeded - Payment was successful
payment_intent.payment_failed - Payment failed
customer.subscription.created - New subscription
customer.subscription.deleted - Subscription canceled
invoice.payment_succeeded - Subscription payment processed
Red flag answer:
We handle all events the same way
I'm not sure which events we listen for
No documented list of handled events
Why it matters: Services send MANY event types. If you don't know which ones you handle, you might:
Miss critical events (subscription.canceled)
Process events you shouldn't (test events in production)
Waste resources processing irrelevant events
Pro tip: Ask the Agent to list ALL events your webhook(s) handles and what action each one triggers. And write the details out to a running document in a MyDocs folder which is NOT accessible to the public. Keep referring to this as you build out your app.
-
Are we handling ALL the important events, not just the happy path?
What you're checking: You're not just handling successful payments, but also failures, refunds, disputes, cancellations, etc.
Common mistake: Only handling payment_intent.succeeded but not payment_intent.payment_failed. This means your app knows when payments work but has no idea when they fail!
Good answer includes:
We handle success events: [list]
We handle failure events: [list]
We handle cancellation events: [list]
We handle refund/dispute events: [list]
For any webhook integration, ask about these categories:
Success
Failure
Cancellation
Reversal
Updates
Expiration
Not every service has all categories, but if a category exists for your service and you're not handling it - that's a gap.
Why it matters: The "happy path" is often 80% of traffic but 20% of the complexity. The edge cases (failures, disputes, cancellations) are where money gets lost and customers get angry.
-
What happens if we get an event type we don't recognize?
What you're checking: Unknown events don't crash your app.
Good answer includes:
Unknown events are logged and ignored
We return 200 OK even for events we don't process
We can add new event handlers without breaking existing ones
Why this matters: Services add new event types all the time. Your webhook should handle events it doesn't recognize gracefully instead of crashing.
Pro tip: Log unknown events - they might be NEW events from the service that you SHOULD handle. Periodic review of "unhandled event" logs helps you catch gaps.
-
Do we respond quickly enough?
What you're checking: Your webhook responds within 30 seconds (ideally within 5 seconds).
Good answer includes:
We respond with 200 OK immediately
Heavy processing happens in the background
Response time is under 5 seconds
Bad: Receive → Email → Database → SMS → PDF → Respond (45s)
Good: Receive → Respond (0.5s) → Queue background job → Done! → Email, DB, SMS, PDF
The beginner takeaway: Respond first, work later. Your webhook's only job is to say "got it" quickly. Everything else happens in the background.
-
Are we doing heavy processing in the background, not blocking the response?
What you're checking: Time-consuming tasks don't block the webhook response.
Good answer includes:
We queue background jobs for heavy processing
We use a job queue system (Replit's built-in or external)
Webhook responds immediately, processing happens async
Heavy tasks that should be in background:
Sending emails
Generating PDFs
Making API calls to other services
Processing large amounts of data
Updating external systems
Light tasks that can happen immediately:
Storing the webhook data in database
Validating the signature
Checking for duplicates
Returning 200 OK
-
How do I see what webhooks we received?
What you're checking: You have visibility into incoming webhooks.
Good answer includes:
All webhooks are logged to the database with timestamp
You can view webhook history in the admin dashboard
We log event type, status, and processing result
Red Flag answer:
Check the console logs
We don’t log webhooks
We only log errors
What to log for each webhook:
Event ID
Event type
Timestamp received
Processing status (success/failure)
Error message (if failed)
Response time
Log identifiers, not data. Store "customer_id: cus_123" not "customer_email: john@example.com"
Why it matters: When something goes wrong at 3 AM, logs are how you figure out what happened. "A webhook failed" vs "Webhook evt_abc123 (payment.succeeded) failed at 3:02 AM with error: database timeout" - which would you rather debug?
Bonus points:
Logs are retained for X days
Old logs are automatically cleaned up - pay attention to this
-
Can I replay a failed webhook to test?
What you're checking: You can recover from failures without losing customer data or asking customers to repeat actions.
Good answer includes:
Failed webhooks can be replayed from the admin dashboard
You can replay webhooks from the service's dashboard (Stripe, etc.)
We store the full webhook payload for replay
Why this matters: A webhook fails because your database was briefly down. You fix the database. Now you need to replay that webhook so the order gets marked as paid.
IMPORTANT: If storing payloads for replay:
Encrypt sensitive data at rest
Set retention limits (don't store forever) - pay attention to this. Could come back to bite you later
Audit who can trigger replays.
Ask the Agent to confirm if such data is encrypted at rest etc.
-
Are we logging enough to debug issues without logging sensitive data?
What you're checking: Logs are helpful but don't expose customer data.
Good answer includes:
We log event metadata but not full customer details
Sensitive fields (like credit card info) are not logged
We log enough to trace the webhook flow
Red Flag answer:
We log the full request body
We log everything for debugging
No mention of data sensitivity
Safe to log:
Event ID: evt_1234567890
Event type: payment_intent.succeeded
Customer ID: cus_ABC123
Amount: $50.00
Status: success
NOT safe to log:
Credit card numbers (log last 4 only: ****4242)
CVV codes (never store these at all)
Social security numbers
Passwords/tokens
Full customer addresses (log city/country only, or hash it)
Email addresses (log domain only: ***@gmail.com)
Phone numbers (log last 4: ***-**-1234)
Why it matters: Logging PII can violate GDPR, CCPA, and PCI-DSS. Even if you're small, getting this wrong early creates a mess to clean up later.
-
How do I test webhooks locally during development?
What you're checking: You can test webhooks without deploying.
Good answer includes:
We use [service]'s CLI to forward webhooks locally
We can trigger test events manually
We have a way to see what webhooks arrived
On Replit, your app is already publicly accessible. Point the webhook URL to your Replit preview URL. For Stripe, you can also use `stripe listen --forward-to [url]` and trigger test events with `stripe trigger payment_intent.succeeded`.
Checkyour server logs to confirm webhooks are received.
-
Is there a way to simulate events?
Why it matters: Testing with real transactions means real money, real customers, and real consequences when things break. Test mode lets you break things safely.
Good answer includes:
The service has a test mode with test API keys
We can trigger test events from the service dashboard
We have a local testing endpoint that accepts sample payloads
Example testing flow:
Use test API keys (e.g. Stripe gives you test keys)
Make a test payment with card number 4242 4242 4242 4242
Webhook fires with test data
Verify your app handles it correctly
No real money involved!
Check if the service (Stripe, PayPal, Twilio etc.) have a Sandbox environment and learn how to use it.
Common Webhook Mistakes (And How to Avoid Them)
Mistake #1: No Signature Verification
The Problem: Anyone can send fake webhooks to your endpoint.
The Fix: Always verify signatures using the service's official library. Let the Agent confirm this.
Mistake #2: No Duplicate Detection
The Problem: Same webhook processed twice = customer charged twice.
The Fix: Store event IDs and check before processing. The Agent handles this during implementation, ask to confirm.
Mistake #3: Slow Response Times
The Problem: Webhook takes 60 seconds to respond → timeout → service retries → duplicate processing.
The Fix: Respond with 200 OK immediately, process in background. Depending on the complexity of your app, you should be aware how it scales.
Mistake #4: Only Handling Success Events
The Problem: You know when payments succeed but have no idea when they fail.
The Fix: Handle ALL important events: success, failure, refunds, disputes, cancellations. Conform with the Agent.
Mistake #5: No Logging
The Problem: Webhook fails and you have no idea what happened.
The Fix: Log every webhook with status and error messages. Confirm with the agent if this is being done and how you can access the data.
Mistake #6: Can't Test Locally
The Problem: You have to deploy to production to test webhooks.
The Fix: Use the service's CLI or test mode, if they have one, to test locally.
Putting It All Together: Your Pre-Deployment Checklist
The Webhook Deployment Checklist
Use this checklist before deploying any app with webhooks to ensure you don't miss critical features.
Security
- Webhook verifies signatures from the service
- Invalid signatures are rejected
- Rate limiting is in place
Reliability
- Duplicate webhooks are detected and skipped (idempotency)
- Failed processing doesn't cause infinite retries
- Plan in place for missed webhooks (service retries)
Data
- All important event types are handled (success AND failure)
- Unknown event types don't crash the app
- We know exactly what events we're listening for
Timing
- Webhook responds within 5-30 seconds
- Heavy processing happens in background jobs
Logging
- All webhooks are logged with timestamp and status
- Failed webhooks can be replayed
- Logs don't expose sensitive customer data
- Admin dashboard shows webhook history
Testing
- Tested locally with service's CLI or test mode
- Tested all important event types
- Tested duplicate webhook handling
- Tested timeout scenarios
- Tested with invalid signatures
Before deploying, verify ALL boxes are checked!
Wrapping Up
When you ask an AI to, for example, "add Stripe payments" or "set up subscriptions," webhooks are often part of the solution - even if you didn't ask for them. That's the nature of Vibe Coding: the AI handles the technical decisions. But webhooks are easy to get wrong, even for AI agents. That's why these 15 questions matter. You don't need to understand the technical details - you just need to verify the AI's work. Before you deploy any feature involving payments, subscriptions, or external services, run through this checklist. Your customers (and your bank account) will thank you. The pattern: Ask → Check the answer → Deploy with confidence.
