An RJ45 tester is the tool that ends the oldest argument in home networking: is it the cable? This page lists the models worth owning and the exact wire order they check - because a tester is only as useful as your ability to read what it says.
Verdict: The cheapest way to prove a cable is dead - and nothing more.
Fits: A drawer backup for the occasional patch cable check.
Check 902074 price on AmazonAmazon search link - we earn nothing from it (no affiliate account on this category yet); specs above are from public product pages.
Verdict: The default home-network tester: fast pass/fail with fault location.
Fits: Homeowners and small-office patch panels - the gift that ends "is it the cable?" arguments.
Check VDV526-100 price on AmazonAmazon search link - we earn nothing from it (no affiliate account on this category yet); specs above are from public product pages.
Verdict: LAN Scout Jr. plus coax ports - the right pick when TV cable shares the drawer.
Fits: Homes mixing ethernet with coax (cable TV / MoCA adapters).
Check VDV526-052 price on AmazonAmazon search link - we earn nothing from it (no affiliate account on this category yet); specs above are from public product pages.
Verdict: The feature cliff: length measurement, POE detection and NCV in one handheld.
Fits: Anyone running or repairing cable professionally part-time - the best value in the list.
Check NF-8209 price on AmazonAmazon search link - we earn nothing from it (no affiliate account on this category yet); specs above are from public product pages.
T568B is the de-facto standard for new installs (T568A survives in government and existing phone-line retrofits). What matters practically: both ends must match. A-B ends produce a crossover cable - harmless on modern gear with auto-MDIX but a genuine trap on older hardware. And the four "white-stripe" conductors are where terminations go wrong: if pin 3 and pin 5 conductors swap, the cable passes a cheap tester and fails a gigabit negotiation - that is a split pair, and only testers with the detection circuitry will tell you.
The tier logic behind these picks (and what length and POE testing add) is broken down in the buying guide; if the tester says the cable is fine but the network still fails, the fault is upstream - the ethernet troubleshooting ladder picks up from there.
All eight conductors, against the T568B order: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown. Both ends must match; a tester reports opens (broken conductor), shorts (two touching), crossed (two swapped) and split pairs (a pair split across two pairs - the sneaky one).
RJ11 is the telephone connector; combo testers include it because the same tool covers phone lines and DSL modems. The RJ45 port is the one for ethernet - wider, eight pins.
Not by looking - the category lives in the cable jacket print and the manufacturing tolerance, not in the wiring. A professional tester certifies a run to a category standard; cheap testers only verify wiring order.
An open means one conductor is cut or not making contact. On a patch cable, replace it. On a run, check the two terminations first - re-punch or re-crimp both ends before chasing the middle of the cable; most opens live within two centimeters of a plug.
You need a tester that checks the shield connection, not necessarily a grounded one. If the spec does not mention shield testing, assume it does not do it.