SD and microSD cards are faked exactly like USB flash drives, with hacked firmware reporting a small amount of real flash as a huge capacity, and they are tested with almost exactly the same software. What changes is only which program fits your computer. This page is the platform map: Windows, Mac, Linux, Android, Chromebook, and the mythical “online” option, each with its right tool, its honest limit, and a link to the full guide. One line holds the whole map together: every platform has an answer, none of them is a website. A browser has no raw access to your card, so every real test below is a local program run on a real computer.
Keep the goal in view while you choose. A quick screen tells you fast whether a card is obviously fake. A full test writes across the claimed capacity and verifies everything, which is the only proof that stands up for a refund or for trusting a card with a camera’s day of photos. Screens sample; full tests fill. Identification tools describe the controller without proving capacity. Every row in the matrix should be read in those terms, and any card that will hold something irreplaceable deserves a full test on whichever platform you have, through the best reader you own.
The platform matrix
| Platform | Recommended tool(s) | Method | Destructive? | Thoroughness | Cost |
|---|---|---|---|---|---|
| Windows | FakeFlashTest | Quick marker screen from the end; Test Empty Space fills free space | Quick: yes; Empty Space: designed to preserve files | Quick screen | Free (freeware) |
| Windows | H2testw | Writes across whole available space, then verifies | Uses available space; back up first | Full verification | Free |
| Windows | ValiDrive | Random spot checks plus speed measurement | Normally no, on a good drive | Spot check | Free |
| macOS | F3 (f3write + f3read) | Fills device with test files, then verifies | Fills device; back up first | Full test | Free (open source) |
| Linux | F3 (f3write + f3read; f3probe probe) | Fills and verifies; probe is a quicker experimental check | Fills device; back up first | Full test | Free (open source) |
| Android | No equivalent full test built in | Reported-capacity display and speed benchmarks only | No | Sanity checks only; cannot prove capacity | — |
| ChromeOS | Files app manual fill test | Fill drive manually, then verify earliest files | Fills drive; back up first | Manual workaround | Built in |
| Online / browser | None exists | No raw block access from a browser | — | No real test possible | — |
Windows and Mac: the two complete toolkits
On Windows you have the full ladder. Start a new card with FakeFlashTest, freeware by Steve Si, portable, run as Administrator, latest v1.1.5 being the latest Beta, from our download page, following how to test a microSD card for fake capacity. Promote survivors to H2testw for proof, use ValiDrive for a normally non-destructive spot check with a speed view, and add ChipGenius only for controller identification, never as capacity proof. The comparisons FakeFlashTest vs H2testw, FakeFlashTest vs ValiDrive, and FakeFlashTest vs ChipGenius sort the ladder rung by rung, and reading FakeFlashTest results correctly is what turns a screen into a decision.
On a Mac, F3 is the whole toolkit and it is enough: install it with Homebrew, fill the card with f3write, verify with f3read, and you hold a full proof, as walked through in how to test an SD card on a Mac. Linux uses the identical F3 workflow, with f3probe as a quicker experimental probe for a first signal, per how to test a USB drive on Linux and the method comparison in FakeFlashTest vs F3. On both systems, identify the correct device twice before filling anything, use a dependable reader such as those via card reader options or the SanDisk route at the SanDisk store for genuine replacements, and keep a backup habit with a service such as pCloud for the files that matter most.
Phones, Chromebooks, and the online myth
Android’s row in the matrix is deliberately sobering. An app can display the capacity the card reports, which is precisely the number the firmware fakes, and can benchmark speed, which is a clue and never a proof. There is no built-in equivalent full capacity test, so the definitive test happens on a computer, as testing an SD card on Android explains without inventing capabilities phones do not have. ChromeOS cannot run the Windows tools either; its Files app manual fill test in checking a flash drive on a Chromebook catches obvious fakes, with a borrowed PC as the settlement step. And the online row is empty for a principled reason set out in the online fake flash test explainer: no web page can test your card.
Whichever platform tested your card, the ending is the same. A full-test pass earns trust, with normal backups. Any fail means stop, preserve the output, and follow what to do next when a fake drive is confirmed, applying the same steps to suspicious bulk drives in the fake SSD guide. The wider hub at best fake USB drive test tools and the alternatives list in H2testw alternatives complete the picture. Find your platform in the matrix, run its real tool to the finish, and never let a card’s claimed capacity, on any screen, stand in for a test.
One arrival routine for every platform
Whichever row of the matrix is yours, the routine on arrival is identical. Unbox the card, put it in your best reader, back up nothing because it is still empty, and run your platform’s real test to completion before the card takes its first real job. Keep the result with the receipt until the return window closes. Cards that pass fully can be labelled with their tested date and trusted with normal backups. Cards that fail go back, with the test output attached to the claim. That single habit, applied on any platform, removes almost all of the risk that fake capacity ever reaches your photos, your work, or your backups.