# Custom fatal error handler in SLIM4

**URL:** <https://discourse.slimframework.com/t/custom-fatal-error-handler-in-slim4/6205>\
**Category:** Questions\
**Created:** [February 7, 2026, 8:12am UTC](https://discourse.slimframework.com/t/custom-fatal-error-handler-in-slim4/6205 "2026-02-07T08:12:59Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![inf3rno](https://avatars.discourse-cdn.com/v4/letter/i/8491ac/32.png) [@inf3rno](https://discourse.slimframework.com/u/inf3rno)\
**Post date:** [February 7, 2026, 8:12am UTC](https://discourse.slimframework.com/t/custom-fatal-error-handler-in-slim4/6205/1 "2026-02-07T08:12:59Z")

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I am developing a REST API and want to support only JSON responses. I added a custom error handler this way:

```auto
$errorMiddleware = $app->addErrorMiddleware($config['error']['debug'], true, $config['error']['log']['communication']);
$errorMiddleware->setDefaultErrorHandler($container->get(ErrorHandler::class));

```

It works, but every now and then I got a fatal error, which is rendered by the default HTML renderer and I guess it is not logged as well. Is there a way to handle fatal errors with a custom error handler?

I know from my own frameworks, that this is a tricky question, because if the custom handler raises an error, then the code can collapse into an infinite error loop… But I still want to do this.

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**Author:** ![LLEGAZ](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.slimframework.com/llegaz/32/1665_2.png) [@LLEGAZ](https://discourse.slimframework.com/u/LLEGAZ)\
**Post date:** [April 3, 2026, 9:48pm UTC](https://discourse.slimframework.com/t/custom-fatal-error-handler-in-slim4/6205/2 "2026-04-03T21:48:07Z")

</div>

Hello sorry late answer I didn’t receive mailing notifications from here anymore

I have a start of an approach but I know it is far from perfect and is going to bully me again for pointing that old, dusty project of mine BUT I intend to release soon (as soon as I’m able… with low health it is gonna be quite challenging yay !) a new slim repository project on my GitHub ! With hopefully a better version of that and tools embedded focus on REST APIs development.

You can extend slim default ErrorHandler into more specialized Handlers  
for instance:

> <https://github.com/llegaz/zelty-php-test/blob/main/src/Handlers/HttpErrorHandler.php>

> <https://github.com/llegaz/zelty-php-test/blob/main/src/Handlers/ShutdownHandler.php>

and then register them for your app to use (as middlewares),  
I personally used an intermediary middlewares.php file:

```php
// Create Error Handler
$errorHandler = new HttpErrorHandler($callableResolver, $responseFactory);
$errorHandler->forceContentType('application/json');

// Create Shutdown Handler
$shutdownHandler = new ShutdownHandler($request, $errorHandler, $displayErrorDetails);
register_shutdown_function($shutdownHandler);

// Add Misc Middleware(s)
….

// Add Routing Middleware
$app->addRoutingMiddleware();

// Add Error Handling Middleware
$errorMiddleware = $app->addErrorMiddleware($displayErrorDetails, false, false);
$errorMiddleware->setDefaultErrorHandler($errorHandler);

```

and then in index.php

```php
// Register middleware
$middleware = require APP_ROOT . '/src/middlewares.php';
$middleware($app, $request);

```

From what I remember I mostly followed Slim 4 documentation..

(But I have to admit I may not be totally sharp or accurate on slim best practices, I’m still learning and didn’t practice for years now, plus the thing I didn’t push any project with slip in production… for now, but I will re-examine documentation and code snippets in the near future so I will probably update here and give you more feedback on all this 🙂 )

The sole time I tried slim was on the zelty php test years ago (I failed), but I loved slim really much (and yes @tj_gumis you were right that rushed 1 week code is quite ugly).

Cheers !

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<div class="post-metadata">

**Author:** ![inf3rno](https://avatars.discourse-cdn.com/v4/letter/i/8491ac/32.png) [@inf3rno](https://discourse.slimframework.com/u/inf3rno)\
**Post date:** [April 4, 2026, 8:12pm UTC](https://discourse.slimframework.com/t/custom-fatal-error-handler-in-slim4/6205/3 "2026-04-04T20:12:32Z")

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Hi!

Thanks, I’ll try it out. Happy Easter! 🙂