Mailchimp Webhook Handler

Parse and handle Mailchimp webhook payloads. Typed events, secret verification, event listeners, zero dependencies, PHP 8.5+.

Author: Chimpmatic

Why This Exists

Mailchimp sends webhook notifications when subscribers join, leave, update their profile, change their email, or get cleaned from your audience. Parsing these payloads means dealing with nested form data, extracting merge fields, and routing events to the right handler.

This library turns raw $_POST data into typed, readonly objects with a clean event listener API.

Built for Contact Form 7 to Mailchimp integrations, but works with any PHP application.

Requirements

• PHP 8.5 or higher (uses readonly classes and enums)
• No extensions required (zero dependencies)

A fatal error (E_USER_ERROR) is triggered if loaded on PHP < 8.5. The library will not run on older versions.

Installation

composer require chimpmatic/mailchimp-webhook-handler

Quick Start

use Chimpmatic\WebhookHandler\WebhookHandler;
use Chimpmatic\WebhookHandler\WebhookEvent;
use Chimpmatic\WebhookHandler\WebhookPayload;

$handler = new WebhookHandler();

// Register listeners
$handler->on(WebhookEvent::Subscribe, function (WebhookPayload $payload): void {
    echo "New subscriber: {$payload->email}";
    echo "Name: {$payload->getMergeField('FNAME')} {$payload->getMergeField('LNAME')}";
});

$handler->on(WebhookEvent::Unsubscribe, function (WebhookPayload $payload): void {
    echo "Unsubscribed: {$payload->email} — reason: {$payload->getReason()}";
});

// Handle the incoming webhook
$payload = $handler->handle($_POST);
echo $payload->getSummary();

Supported Events

Event	Mailchimp Type	Description
Subscribe	subscribe	New subscriber added
Unsubscribe	unsubscribe	Subscriber removed
ProfileUpdate	profile	Subscriber updated their profile
EmailChanged	upemail	Subscriber changed their email
Cleaned	cleaned	Email bounced (hard/soft)
Campaign	campaign	Campaign sent to list

Webhook Endpoint

use Chimpmatic\WebhookHandler\WebhookHandler;
use Chimpmatic\WebhookHandler\WebhookException;

$handler = new WebhookHandler('your-webhook-secret');

// Mailchimp sends a GET request to validate the URL
if ($handler->isValidationRequest($_SERVER['REQUEST_METHOD'])) {
    http_response_code(200);
    exit;
}

// Verify the secret (Mailchimp appends ?secret=... to the URL)
if (!$handler->verifySecret($_GET['secret'] ?? '')) {
    http_response_code(403);
    exit;
}

try {
    $payload = $handler->handle($_POST);
    http_response_code(200);
} catch (WebhookException $e) {
    http_response_code(400);
    echo $e->getMessage();
}

Working with Payloads

$handler->on(WebhookEvent::Subscribe, function (WebhookPayload $payload): void {
    // Basic info
    echo $payload->email;       // "john@example.com"
    echo $payload->audienceId;  // "abc123def4"
    echo $payload->firedAt;     // "2026-03-16 21:00:00"
    echo $payload->event->value; // "subscribe"

    // Merge fields
    echo $payload->getMergeField('FNAME'); // "John"
    echo $payload->getMergeField('LNAME'); // "Doe"

    // Full summary
    echo $payload->getSummary();
    // "[2026-03-16 21:00:00] subscribe — john@example.com (audience: abc123def4)"
});

Email Changed Events

$handler->on(WebhookEvent::EmailChanged, function (WebhookPayload $payload): void {
    echo "Old: {$payload->getOldEmail()}"; // "old@example.com"
    echo "New: {$payload->getNewEmail()}"; // "new@example.com"
});

Listen to All Events

$handler->onAny(function (WebhookPayload $payload): void {
    // Log every webhook
    error_log($payload->getSummary());
});

Parse Without Dispatching

// Just parse, don't trigger listeners
$payload = $handler->parse($_POST);

if ($payload->isSubscribe()) {
    // ...
}

Error Handling

use Chimpmatic\WebhookHandler\WebhookException;

try {
    $handler->parse($_POST);
} catch (WebhookException $e) {
    // Empty payload, missing type, unknown event type, invalid data
}

Related Packages

• mailchimp-api-key-validator — Validate API key format and connectivity
• mailchimp-audience-finder — Find Audience IDs and merge fields
• mailchimp-subscriber — Subscribe contacts with merge fields

Links

• Packagist
• GitHub
• Issues
• Connect Contact Form 7 with Mailchimp
• How to Get Your Mailchimp API Key
• Mailchimp Audience Fields and Merge Tags
• Chimpmatic — Contact Form 7 to Mailchimp

License

MIT License. Copyright (c) 2026 Chimpmatic.