How to Fix a Slow Website: Diagnose Problems Using The Browser
This first part of the series shows you how to uncover what actually slows your pages down — using simple, non-technical tools built into every modern browser.
Thu Nov 13 2025 • 5 min read
This article is the first part of a series about fixing slow websites.
We start here by diagnosing the problems using the browser. Everything you need to understand your site’s speed is already built into Chrome, Edge, or Firefox.
This guide walks you through that process step by step, in plain language, with no assumptions.
Begin With a Clean Load
Whenever you want to check why a page feels slow, the first thing to do is open it in an incognito window. This removes plugins, cached files, and anything else that could influence the results. You’re trying to recreate what a first‑time visitor experiences.
Once the page loads, open DevTools (right‑click → Inspect) and switch to the Network tab. Don’t worry about the details yet — just look at the long table and the colorful timing bars. This is your page loading in real time.
Reading the Network Waterfall
The waterfall is simply a timeline: each row is a file, and each colored bar shows how long that file took to load. If something feels slow, the waterfall always reveals why.
A quick example: imagine you load your homepage and notice a large purple bar stretching almost the full width of the screen. When you check the “Size” column, you see it’s a 3.4 MB JPEG used as a hero image. Suddenly the slowness makes perfect sense.
Try the same: sort by Size, then by Time, and look for patterns. Which files are the heaviest? Which ones take longest to respond? Does something seem out of place — maybe a large font file or a script from a service you forgot you were using?
You don’t need to fix anything yet. Right now you’re just learning the shape of your page.
What the Columns Actually Mean
A lot of people open the Network panel and feel overwhelmed, so here’s a quick cheat sheet:
- Name shows the actual file the browser requested.
- Status tells you whether it loaded successfully.
- Type is the kind of file: image, script, stylesheet, etc.
- Size reveals how heavy it is.
- Waterfall shows how long it took and when it started.
Five columns — that’s it. Most performance issues become obvious once you know how to read these.
Move to the Performance Panel (This Shows What the Browser Does)
While the Network tab shows what comes into the browser, the Performance tab shows what the browser does after it arrives.
Click Performance, hit Record, and reload the page. After a second or two, stop the recording.
You’ll see a timeline filled with color. Even if it looks messy, one detail matters most: the yellow sections. Yellow means your browser is busy running JavaScript — and heavy JavaScript is one of the top reasons websites feel slow.
Long yellow blocks usually point to:
- Third‑party scripts (analytics, chat widgets, A/B testing tools).
- Large bundles from your theme or framework.
- Code that blocks the page from drawing content.
Below the timeline, you may also see purple areas — these represent the browser painting pixels on the screen. If they’re large or repeated, your layout might be expensive to render (often caused by very large images or complex structures).
Again, we’re not fixing. We’re just identifying what demands your browser’s attention.
Unused Code: A Quiet Performance Drain
Another useful tool lives under More Tools → Coverage. Open it, click Reload, and the browser will tell you how much of each file your page actually uses.
It’s normal for a site to have some unused code. But when you see something like “85% unused CSS” or “70% unused JavaScript,” it’s a sign you’re loading much more than you need.
This doesn’t mean you must delete anything. But these numbers give you a sense of where your weight comes from.
Test as a Mobile User
Most visitors load your site on a phone, not a laptop. And phones — especially older ones — are slower.
You can simulate this directly in the browser: use the Network throttling dropdown and choose Slow 3G. Reload the page.
This will feel uncomfortably slow at first, which is the point. If a single image takes several seconds to appear, or the first text takes too long to show up, you’ve uncovered issues your metrics alone can’t describe.
Pay attention to what happens first. Does an empty layout sit there for too long? Does the page jump around once images load? Does text shift when fonts arrive? These small behaviors form the real user experience.
Putting It All Together
By now you’ve seen:
- which files are large,
- which ones take the longest,
- what your browser struggles to compute,
- how much of your code actually gets used,
- and how your site behaves under slow conditions.
Diagnosis is exactly this: learning the story behind the slowness.
A heavy image isn’t just a number in a table — it’s the reason the first screen feels empty for a full second. A busy JavaScript bundle isn’t just a file — it’s why your buttons feel unresponsive. These clues add up.
In the next article, we’ll talk about one of the biggest and easiest problems to fix: images. Most slow websites begin there.
