What Is a Webhook? How Apps Talk to Each Other in Real Time

By the LaunchLen Web Solutions Team · Kitchener, Ontario · Last updated: November 4, 2026

A webhook is a way for one application to notify another as soon as something happens. Instead of the second app asking “anything new?” over and over, the first app sends a message to a URL you control when an event occurs: a form is submitted, a payment succeeds, a booking is created.

This guide explains webhooks in plain English, how they differ from API polling, common business uses, and the reliability and security habits that keep them trustworthy.

Webhooks in plain English

At a high level:

• You register a callback URL with the sending system (the endpoint that will receive events).
• When an event happens, the sender sends an HTTP request to that URL, usually with a JSON body describing what changed.
• Your code reads the payload, checks that it is authentic, then updates your CRM, starts a workflow or queues a job.

The important idea is push on event, not “check later.” That is why webhooks feel closer to real time than a nightly sync.

Webhooks are one building block among many in integrations. For a broader view of connecting business systems, see our guide to system integration for small business.

Webhook vs API polling

People often say “webhook vs API” as if they were opposites. In practice, webhooks usually travel over the same web technologies as APIs. The difference is who starts the conversation.

• API polling: Your system repeatedly calls another system’s API to ask whether anything changed. Simple to reason about, but you pay for empty checks and you only learn about events as often as you poll.
• Webhooks: The other system calls you when something happens. Fewer empty checks, faster notice, but you must keep an endpoint online and handle retries and duplicates.

Many products offer both: webhooks for timely events and APIs for lookups, backfills and repairs. Choosing between them (or combining them) depends on how fresh the data must be and how reliable each vendor’s delivery is.

Common business examples: forms, payments, bookings

Illustrative patterns (not a client list):

• Forms: A website form sends a webhook when someone requests a quote, so your CRM creates a lead without a manual export.
• Payments: A payment provider notifies your app when a charge succeeds or fails, so fulfilment and receipts stay in sync.
• Bookings: A scheduling tool notifies your system when an appointment is booked or cancelled, so reminders and staff calendars update.

The same pattern shows up in automation and agent-style workflows: an event arrives, your code decides what is allowed, then a controlled action runs. That sits alongside the ideas in AI process automation vs RPA vs agentic AI.

Reliability: retries, duplicates, logging

Networks fail. Senders therefore retry. Your receiver should assume the same event may arrive more than once.

Habits that can include:

• Idempotency. Store an event id and ignore duplicates you have already processed.
• Fast acknowledgement. Accept the webhook quickly, then do heavy work in a queue so the sender does not time out and retry needlessly.
• Structured logs. Keep enough detail to replay or audit what happened, without stuffing secrets into the log line.
• Dead-letter handling. When processing fails after retries, park the event for a person or a repair job.

We do not state a fixed place where those logs live; that depends on the services a project uses.

If your receiver needs a small server or VPS, pick what fits the workload. Disclosure: LaunchLen has a referral relationship with Hostinger for hosting, VPS and self-hosted automation. Our recommendations stay based on your needs.

For new clients we do not take system access by default; credentials apply when integrating an existing codebase, micro-SaaS or servers. Discovery for an integration can be agreed with you: full requirements gathering, understanding the business, spotting what can be automated, and mapping analog or handwritten steps that can be digitized.

Security: signatures and secrets

Anyone who discovers your callback URL might try to post fake events. Defences that can include:

• Shared secrets and signatures. Many providers sign the payload so you can verify it came from them.
• HTTPS only. Encrypt data in transit to your endpoint.
• Allowlists and private networking where the platform supports them.
• Least privilege. The handler should only perform the actions that event type requires.
• Rotation. Change secrets when people leave or a leak is suspected.

Never put webhook secrets in front-end code or public repositories.

FAQ

Is a webhook the same as an API?

They often use HTTP and JSON, but the direction differs. An API call is usually your system asking for data or requesting an action. A webhook is the other system notifying you that something already happened.

What if my endpoint is briefly down?

Most senders retry for a period. You should still design for missed events: a manual replay tool, a periodic reconciliation job, or both.

Do I need webhooks for every integration?

No. Low-volume or batch processes can poll on a schedule. Webhooks help when delays are costly and the sender supports reliable delivery.

Let’s work together on your project

Connecting forms, payments or bookings so your tools stay in sync? We’re LaunchLen Web Solutions Inc.

Based in Kitchener, serving Waterloo Region and businesses across Ontario.

Our Software Development page explains custom software development in Kitchener-Waterloo and across Ontario: internal tools, customer-facing apps, integrations and AI features that connect to the systems you already rely on. Before any build, we can agree the scope, deliverables and reporting with you. Book a free consultation to get started.