H2testw for Mac: what to use instead

Short answer

There is no h2testw for Mac. It's a Windows utility, written by Harald Bögeholz for the German computing magazine c't, and no macOS version has ever shipped. If you landed here searching for a download, that's the honest answer — and the rest of this page is what to do instead.

You have three real choices: run h2testw inside a Windows VM, use F3 in Terminal, or use a native Mac tool with a graphical interface. All three do fundamentally the same thing, and the third is what we built.

What h2testw actually does, and why it matters

H2testw fills a drive's free space with files containing known, verifiable data, then reads every byte back and compares it against what it wrote. That sounds mundane. It's the only method that works.

The reason is that a counterfeit flash drive lies at the firmware level. Its controller reports 1TB to your operating system while the actual memory chip inside might hold 32GB. Every tool that asks the drive how big it is — Disk Utility, System Information, Finder's Get Info — gets told 1TB and believes it. The lie is only exposed by writing past the real capacity, at which point the drive quietly wraps around and overwrites what you stored earlier.

Every option, compared honestly

If you're comfortable in Terminal, use F3

We'd rather point you at the right tool than pretend ours is the only one. F3 (Fight Flash Fraud) is open source, well maintained, and does the job properly on macOS:

brew install f3

# Full write-and-verify across the whole card (slow, thorough)
f3write /Volumes/UNTITLED
f3read  /Volumes/UNTITLED

# Or a fast binary-search probe for the wraparound point
sudo f3probe --destructive --time-ops /dev/disk4

If that command block doesn't faze you, F3 is a completely legitimate answer and you don't need us. The catch is the one you'd expect: you need Homebrew, you need to identify the right device node without destroying the wrong disk, and you need to interpret the output yourself.

If you'd rather not, use ours

Cinder's Drive Integrity & Capacity Test is free, needs no licence or account, and runs natively on macOS and Windows. It performs the same fundamental check:

• Full Sequential Verify — writes and re-checks markers across the entire claimed capacity. Same core approach as h2testw, maximum certainty.
• Fast Boundary Probe — writes markers at doubling offsets and binary-searches for the wraparound, the same technique as F3's f3probe. Flags a fake multi-terabyte claim in seconds rather than hours.
• It writes one visible, clearly-named test file you can watch grow in Finder — nothing hidden — and reports the drive's real usable capacity when the claim turns out to be false.

What to do when a drive fails

Stop using it immediately, and don't try to reformat it into honesty — the lie is in the firmware, and no format fixes that. Request a refund or open a chargeback; a capacity test report is strong evidence for both. Marketplaces generally act on this quickly, because selling misrepresented capacity is straightforward fraud.

If the drive has already been overwriting your files, some of them may still be recoverable — that's the other half of what Cinder does. Scan it and preview what's left for free; you only pay if you want to save it back.

Common questions

Is there a version of h2testw for Mac?

No. It is Windows-only and always has been. Use F3 in Terminal, run h2testw in a Windows VM, or use a native Mac tool like ours.

Can I just check the size in Disk Utility?

No — and this is the single most common mistake. Disk Utility reports the capacity the drive claims, which is exactly the number a counterfeit controls. Only writing and verifying real data exposes the lie.

Will the test erase my files?

A full-capacity test writes across the drive, so run it on an empty or formattable device. Ideally, test a drive the day you buy it.

How long does it take?

A full verify is limited by the drive's write speed — a slow 256GB stick can take a couple of hours. The fast boundary probe usually settles the question in under a minute, which is why we suggest starting there.