How Good Debugging Skills Can Make You a Better Developer

Got a call from a client. Total panic. A crucial “20% OFF” coupon for their wholesale customers wasn’t working. Regular customers? Fine. But the high-volume guys, the ones who keep the lights on, were getting error messages at checkout. For a WooCommerce shop, that’s a five-alarm fire.

Honestly, these are the kinds of problems that really test your debugging skills. It’s not a clean, obvious syntax error. It’s a logic bug buried somewhere deep in the WordPress or WooCommerce core, probably tangled up with another plugin. A real mess.

My first thought? Plugin conflict. It’s the usual suspect. So I did what most of us do when the pressure is on: I started deactivating plugins one by one on the staging site. An hour of that, and I had nothing. Zero. The bug was still there. Here’s the kicker: I knew it was a lazy approach, but I did it anyway. That was my mistake, and it was a total waste of time.

Stop Guessing, Start Debugging

When you’re just flipping switches, you’re not learning anything. You’re just guessing. The real fix, the one that actually makes you a better developer, requires you to see what the code is doing. For PHP, that means one thing: Xdebug. Instead of blindly disabling things, I fired up my local environment, enabled Xdebug, and placed a breakpoint right where WooCommerce validates a coupon.

By stepping through the code line by line, I could watch the data change. I saw the coupon code, the user’s cart, and their user role. And that was it. A custom function, added by a previous developer, was checking user roles but was written in a way that it failed silently if a user had more than one role. The wholesale customers had both a “customer” role and a “wholesale” role. The function saw “customer,” assumed they weren’t wholesale, and invalidated the coupon.

add_filter( 'woocommerce_coupon_is_valid', 'legacy_check_user_role_for_coupon', 10, 2 );

function legacy_check_user_role_for_coupon( $is_valid, $coupon ) {
    // Get the user object
    $user = wp_get_current_user();
    
    // The old code was checking the first role only
    // $user_role = ! empty( $user->roles ) ? $user->roles[0] : '';

    // The FIX: Check if the 'wholesale' role exists in their array of roles
    if ( $coupon->get_code() === 'WHOLESALE20' && ! in_array( 'wholesale', (array) $user->roles ) ) {
        // If it's the specific coupon and they DON'T have the role, invalidate it.
        return false;
    }

    return $is_valid;
}

Without a debugger, I could have spent another three hours on this. With it, I found the exact line of code in about 15 minutes. This is what the folks over at carlalexander.ca were getting at in a recent post; debugging isn’t just about fixing things, it’s a powerful learning tool. You’re not just patching a hole, you’re learning how the entire system works from the inside out.

So, What’s the Point?

Nobody loves debugging for its own sake. We want to build stuff. But if you treat debugging as a chore, you’re missing the point. It’s the single best way to level up your skills. Every weird bug you squash teaches you something new about the platform you’re working on. You move from being a coder who copies snippets to a developer who understands the architecture.

• Stop brute-forcing: Deactivating plugins is a last resort, not a first step.
• Use a real debugger: Learn to use Xdebug or your IDE’s equivalent. It feels slow at first, but it’s infinitely faster in the long run. Trust me on this.
• Embrace the process: Every bug is a chance to learn the “why” behind the code, not just the “what.”

Look, this stuff gets complicated fast. If you’re tired of debugging someone else’s mess and just want your site to work, drop my team a line. We’ve probably seen it before.

What was the bug that finally broke you and made you learn a real debugger?