Why Is My Listener Firing Twice? Laravel 12’s Unique Events Trait Ends the Chaos

Laravel’s event system is powerful—but not perfect. In complex apps, especially those with multiple service providers or packages, you might’ve run into this sneaky bug:

Duplicate event listeners firing multiple times.

It’s subtle. It’s hard to debug. And it can wreak havoc on performance, logging, or business logic.

Laravel 12 introduces a clean fix: the new UniqueEvents trait.

Let’s unpack the problem, the solution, and how to use it.

😵 The Problem: Listener Overlap

In Laravel, you register event listeners like this:

Event::listen(UserRegistered::class, SendWelcomeEmail::class);

But in large apps, this listener might get registered:

In multiple service providers
By multiple packages
Or even dynamically via boot methods

Result?
The same listener fires multiple times for a single event.

This leads to:

Duplicate emails
Double logging
Redundant database writes
Confusing bugs that are hard to trace

🔍 Why It Happens

Laravel doesn’t check for duplicates when registering listeners. If SendWelcomeEmail is registered twice, it’ll run twice.

And since listener registration often happens in boot() or register() methods, it’s easy to accidentally stack them.

✅ The Fix: Laravel 12’s `UniqueEvents` Trait

Laravel 12.31 introduces the UniqueEvents trait. It ensures that each listener is only registered once—no matter how many times you call Event::listen().

🔧 How to Use It

Just add the trait to your service provider:

use Illuminate\Foundation\Support\Providers\EventServiceProvider;
use Illuminate\Support\Traits\UniqueEvents;

class AppServiceProvider extends EventServiceProvider
{
    use UniqueEvents;

    public function boot()
    {
        parent::boot();

        Event::listen(UserRegistered::class, SendWelcomeEmail::class);
        Event::listen(UserRegistered::class, SendWelcomeEmail::class); // Won’t fire twice
    }
}

Even if you accidentally register the same listener multiple times, Laravel will deduplicate it.

🧪 Real-World Impact

Let’s say you have a modular app with multiple providers:

UserServiceProvider registers SendWelcomeEmail
NotificationServiceProvider also registers it

Without UniqueEvents, the listener fires twice.
With it, Laravel ensures it only fires once—no matter how many times it’s registered.

🧙‍♂️ Behind the Scenes

The UniqueEvents trait overrides Laravel’s internal listener registration logic. It tracks registered listeners and prevents duplicates from being added to the event dispatcher.

It’s lightweight, non-invasive, and doesn’t require changes to your existing listener classes.

💡 Developer Tips

Use UniqueEvents in any service provider that registers listeners dynamically or conditionally.
Audit your app for duplicate listener registrations—especially in large codebases.
Combine with Laravel’s ShouldQueue interface to ensure listeners are queued properly and only once.
If you’re building packages, consider using UniqueEvents to avoid polluting the host app’s event system.

🔮 Final Thoughts

Laravel’s event system is elegant—but in real-world apps, elegance needs guardrails.

The new UniqueEvents trait is one of those guardrails. It solves a subtle but serious problem with duplicate listeners, giving you cleaner, safer, and more predictable event handling.

If you’ve ever debugged a “why did this fire twice?” bug, this trait is your new best friend.