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Sospeter Mong'are
Sospeter Mong'are

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Callbacks vs Webhooks When Working with APIs

#api #programming #webdev #beginners

When building or integrating APIs, you’ll often come across two terms that sound similar: callbacks and webhooks. Both involve one system sending data back to another, but they serve different purposes. Let’s break them down.

🔹 What is a Callback Endpoint?

A callback is a URL you provide to an API when making a request. The API uses that URL to send back the result of that specific request.

  • Triggered by: A request you initiated.
  • Used for: Asynchronous responses.
  • Scope: Only for the request that included the callback URL.

👉 Example:
You send a fund transfer request to a banking API (like KCB Buni). Because transfers take time to process, you provide a callback URL (https://yourapp.com/ft-callback). Once the bank finishes processing, it POSTs the result (success or failure) to that callback.

{
  "transactionStatus": "SUCCESS",
  "amount": 100,
  "transactionReference": "CSS472TCP"
}
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✅ Purpose: Tie back the outcome of a request you made earlier.

🔹 What is a Webhook?

A webhook is different. Instead of being tied to a single request, it’s an ongoing subscription to events. You tell the API provider, “Whenever this event happens, send the details to this URL.”

  • Triggered by: An event in the provider’s system.
  • Used for: Real-time notifications.
  • Scope: Continues to work until you unsubscribe.

👉 Example:
With M-Pesa C2B, you register a webhook endpoint like https://yourapp.com/mpesa-callback. Every time a customer sends money to your paybill, M-Pesa automatically sends a notification to that URL — no request needed from you.

{
  "TransactionType": "Pay Bill",
  "TransID": "QW234F",
  "TransAmount": "250.00",
  "MSISDN": "254712345678",
  "BillRefNumber": "INV1023"
}
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✅ Purpose: Keep your system in sync with external events in real-time.

🔹 The Key Difference

  • Callback endpoint → “Tell me the result of this specific request.”
  • Webhook → “Notify me whenever this event happens.”

🔹 Real-World Analogy

Imagine a restaurant:

  • Callback: You place an order online and provide your number. They call you when your order is ready.
  • Webhook: You subscribe to their menu updates. They text you every time they add a new dish, even if you didn’t order anything.

🔹 Why It Matters for Developers

When working with APIs:

  • Use callbacks when your request may take time and you need the outcome.
  • Use webhooks when you want to react automatically to events you didn’t directly trigger.

In practice, many APIs use both. For example, a payments API may:

  • Send a callback with the result of your initiated payment.
  • Offer a webhook for general payment notifications (refunds, reversals, failed debits).

🔹 Best Practices

  1. Secure your endpoints
  • Validate request signatures or whitelist provider IPs.
  • Store raw payloads before processing (helps debugging).
  1. Make endpoints highly available
  • Providers often retry if your server is down, but don’t rely on it.
  1. Log everything
  • Keep track of incoming notifications to resolve disputes later.

✅ Final Takeaway

  • Callback = one-time, request-based response.
  • Webhook = ongoing, event-driven notification.

Both are critical in modern API development — understanding the difference helps you design more reliable integrations.

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