A few years ago, I decided to sort through the box of Ethernet cables I'd accumulated over the years. There were patch cables from old routers, a couple I'd crimped myself, and a handful of cheap ones that came bundled with various devices. They all looked fine from the outside, but about a third of them failed the test. Every single one of those cables had been in rotation at some point, plugged into something in my house, quietly causing problems I'd probably blamed on something else entirely. A basic Ethernet cable tester costs around $20 and takes less than a minute to use, and I'm so glad I keep one in my networking toolbox.

A lot of home networking problems are physical, not digital

The physical layer is to blame for a lot of networking malaise

When a network connection drops, slows down, or behaves inconsistently, the instinct for most people is to look at software first. They restart the router, check for firmware updates, call their ISP, or start messing with DNS settings, and these can all be appropriate troubleshooting steps, but it skips past the most fundamental layer: the physical one.

Ethernet cables are simple, but they're not indestructible. The individual conductors inside are thin copper wires, and it doesn't take much to compromise one. A cable that got pinched behind a desk, stepped on repeatedly, or bent at a sharp angle near the connector can develop an intermittent fault that's almost impossible to diagnose through software alone. You'll see random packet loss, speeds that fluctuate for no obvious reason, or a connection that drops and reconnects every few hours. Run a speed test, and it might look fine one minute and terrible the next. Add in the fact that many cables used today are flat cables, and you introduce a whole new potential set of durability problems.

A continuity tester catches all of this. If a pair is open, shorted, or crossed, the tester flags it immediately. There's no ambiguity here, the cable either passes or it doesn't.

There's a chance you have some bad cables

If it has been years since you installed them, it might be worth checking them

Most people don't buy networking cables with much thought. They grab whatever is cheapest, or they use whatever came in the box with their router or modem. Over time, a household can accumulate them from all kinds of different sources, with varying levels of quality, and this introduces a problem: there's no way to tell a good cable from a bad one just by looking at it.

The connectors might look fine. The jacket might be intact. But inside, a conductor could be broken right where it meets the crimp, or two wires could be making intermittent contact where they shouldn't. This is especially common with hand-crimped cables, where a single pin that didn't seat properly means the cable works most of the time but fails under specific conditions.

If you've hand crimped a bunch of cables, or used flat ones around your home, it's worth testing them. Even before you install them, a cable tester turns it from a guessing game into a five-second check. You can go through every cable you own in an afternoon, label the good ones, and toss the bad ones with confidence.

A cheap $20 tester doesn't cover the gamut of potential issues

There still could be deeper issues lurking

A basic continuity tester simply checks whether all eight conductors are connected end to end and whether they're in the correct pin order, and doesn't do any deeper testing. It won't tell you whether a cable meets Cat5e or Cat6 specifications, it can't measure signal degradation over a long run, and it won't detect crosstalk between pairs. Cable testers that perform those kinds of certification can run well into the hundreds and even thousands of dollars, and aren't really for residential use.

In home networking, most of what you need is basic testing

Continuity is where most problems live

Most residential Ethernet runs are short, usually under 30 feet between a switch and a device. At those distances, crosstalk and signal degradation are rarely the cause of noticeable issues. The problems that actually take down home connections are almost always continuity failures: a broken conductor, a bad crimp, a crossed pair. Those are exactly the kinds of issues that a cheap $20 tester catches, and why it's worth having one around. If you're running cable through walls over longer distances and want to verify performance to spec, a qualifier makes sense, but for simple testing of patch cables, verifying hand-crimped connections, and auditing the pile of cables you've collected over the years, a continuity tester covers the vast majority of real-world failure modes you'll actually encounter at home.

A useful tool that doesn't cost a fortune

If you have a drawer, bin, or box full of Ethernet cables, there is a decent chance at least one of them is not as healthy as it looks. Mine certainly were not. A basic tester will not certify a cable to Cat6 spec or diagnose every possible performance issue, but it will catch the physical failures that cause the most annoying home networking problems. For the price of a takeout meal, it turns that pile of mystery cables into a pile you can actually trust, and that alone makes it worth owning.