A QA Testers Guide to Spotting Bugs in Browser Games

Right, I spent six years doing QA at a mobile game studio in Manchester before the 2024 redundancies. I broke games for a living. After getting laid off I picked up freelance QA work alongside writing for FinanceMass, and one habit I never lost is breaking games while I'm meant to be just playing them.

This guide is the stuff I do automatically when I open a new browser game for review. None of it is secret. Most QA folks I know do the same things. But the patterns are useful for players who want to understand why a game feels off when nothing's obviously broken, and for developers who want to test their own work before shipping.

The five-second test

Before I do anything else, I let the game's first screen sit for five seconds and watch. Most browser games are designed to grab attention. If the first screen doesn't communicate what kind of game this is within five seconds (visual style, suggested controls, basic premise), that's a content-discovery problem and it'll cost the developer players who close the tab before learning what the game is.

While the screen sits, I'm also watching for visual issues. Tearing in animations. Sprites that visibly snap rather than animate. Background music that loops jarringly. Loading indicators that finish but leave behind layout shifts. Any of these signal that the developer didn't sweat the polish, which tends to correlate with broader quality issues throughout the game.

Input lag, measured roughly

Click or tap something. Watch how long it takes for the game to respond. Anything over a hundred milliseconds is going to feel sluggish, especially on a timing-precise game like a platformer or shooter. You can't measure latency precisely without instruments, but you can feel the difference between 50ms and 150ms once you're paying attention.

Clearest test is to start a movement input and immediately end it. If the character keeps moving for a beat after you release the key, the game has accumulated input that wasn't supposed to be there. That's a sign of laggy input processing, which gets worse the more is happening on screen.

The corner-press test

Press every key on the keyboard while the game is in its main play state. WASD. Arrow keys. Shift. Space. Numbers. Enter. Escape. Most games respond to a subset of these. Some respond to keys they don't document, which tells you the developer left in debug functions or hidden modes. A few games crash if you press a key during a specific state, which is the kind of bug a player wouldn't normally trigger but a QA pass would catch on the first attempt.

I've found 'cheat' mode in three games this way over the past year by accident. Most developers leave their dev keys in shipping builds. Not great practice but useful for QA brain.

The window-resize test

Resize the browser window while the game is running. A well-built browser game should either pause itself, scale the canvas appropriately, or maintain its aspect ratio with letterboxing. A poorly-built one stretches the canvas into the new aspect ratio, breaks input mapping because mouse coordinates are now off, or simply crashes.

Resize test is useful because it triggers code paths that the developer probably didn't test for. Most game-testing scenarios assume a fixed window size. Real users resize windows all the time, switch between fullscreen and windowed, or use different display configurations. Robust games handle all of this. Most don't.

The tab-blur test

While the game is running, switch to a different browser tab. Wait thirty seconds. Switch back. The game should pause (or at least visibly handle the blur state) and resume smoothly. Some games keep running in the background, which is fine if the developer planned for it but problematic if the game uses requestAnimationFrame naively and the browser throttles the animation frame rate while the tab is hidden.

I've seen games that ate a hundred percent CPU in the background because they fell back to setInterval when the tab was blurred. Players don't notice this until their laptop fan kicks in. Developers don't notice it because they don't test this scenario.

The mobile test, even on desktop reviews

If the game runs on mobile (most browser games do, even if mobile isn't the primary target), open it on your phone and check the basics. Does the canvas fit the screen right? Are the touch hit-areas big enough for fingers? Does the game freeze when the screen rotation changes? Does it cope with the address bar appearing and disappearing as you scroll on a mobile browser?

Most browser games 'work on mobile' but were designed for desktop. The mobile pass usually reveals at least one issue. Good developers fix these issues. The mid ones leave them in and hope nobody notices.

Audio sanity check

Mute the game, then unmute. Audio should resume smoothly. Some games lose audio entirely after mute-unmute and you have to refresh to get it back. Some keep playing audio that's been started but ignore your unmute. Some have such bad audio sync that you wonder if the audio is from a different game entirely.

The audio side of browser games is hard because the Web Audio API has known quirks across browsers and platforms. Maya wrote about this in detail in her piece on why some games feel slow at 60fps, which I recommend. For QA purposes, I just check that audio behaves sensibly when toggled.

The fifteen-minute lock-in

For a real QA pass I sit with a game for at least fifteen minutes. Most issues show up in the first minute or two. The rest emerge over time. Memory leaks. Animation desyncs as the game runs longer. Specific corner cases in level design. The boss fight that breaks because the music transition fires at the wrong time. Some bugs are sleeping waiting for the right condition to wake them up.

If a game holds up to fifteen minutes without a noticeable degradation, it's probably stable for hours. If it starts feeling worse around minute eight, it'll be feeling much worse around minute thirty.

What I do when I find something

If I'm reviewing for FinanceMass I note the bug, try to reproduce it, and decide whether it affects the verdict. A bug that breaks playability gets called out in the review. A bug that's edge-case and unlikely for casual players doesn't.

If I'm doing paid QA, I file a clean repro. Steps to reproduce. Expected behaviour. Actual behaviour. Hardware and browser version. Severity rating. The whole thing. Repro quality is what separates good QA from useful QA, and it's the part that takes years to develop the muscle memory for.

If you're a player who just wants to understand why a game feels off, this checklist gives you the vocabulary. The game is laggy. The window resizing breaks input. The mobile version doesn't fit the screen. The audio loops weirdly. None of these are random complaints. They're symptoms of specific QA failures that developers can fix if they're paying attention. Whether they are paying attention is the question this site's reviews try to answer.