If you are using laravel as api only, you might want to return JSON on every request, even on errors/exceptions. The easiest way to do so is using this middleware globally.

JsonMiddleware.php

<?php 

namespace App\Http\Middleware;

use Closure;
use Illuminate\Http\Request;

class JsonMiddleware 
{
    public function handle(Request $request, Closure $next) 
    {
        $request->headers->set('Accept', 'application/json');
        
        return $next($request);
    }
}
    

If you need 404 also in JSON, update the render function as follows. This solved for me in Laravel 6

app/Exceptions/Handler.php

public function render($request, Exception $exception)
{
        if (substr($request->server()['REQUEST_URI'],1,3) =='api') {
            $request->headers->set('Accept', 'application/json');
        }
        return parent::render($request, $exception);
}

Returns "text/html; charset=UTF-8"

Route::get('/foo', function () {
    return 'hello world';
});