Fake Flash Drive Tester: CLI and Claude Code Skill

Overview

A Windows tool that proves whether a USB flash drive or SD card really holds its advertised capacity, packaged both as a standalone command-line script and as a Claude Code skill. The capacity test writes self-identifying data in doubling stages with unbuffered, write-through I/O and re-reads the entire written range after every stage, so a small fake is caught in an early stage and a wrap-around fake cannot hide. Failures are classified as discarded (zeros), wrap-around (with the real capacity worked out from the wrap distance) or garbage, and reported with claimed size, real size, multiplier and a region map. It refuses the system drive, network and optical drives, and non-empty drives unless told otherwise. Read-only commands identify the drive and list red flags, and check it for malware: autorun and shortcut-worm heuristics, a report-only Microsoft Defender scan, and a BadUSB check that flags keyboard or network functions hiding behind the storage. One standard-library Python file, no installs. 63 tests pass on Python 3.11 and 3.14 on Windows 11; no physical removable drive was tested for this release.

def run_stages(tester, cap, start, out=print):
    """Write in doubling stages up to `cap` bytes, fully re-verifying after each.

    Returns a Verdict whose kind is PASS, FAKE, WRITE-FAIL or READ-FAIL.
    """
    stage = max(int(start) // SEC * SEC, SEC)
    first = True
    while tester.written < cap:
        ok, note, wrate = tester.write_to(min(stage, cap))
        res = tester.verify()
        good = res.counts.get('OK', 0) * SEC
        if res.error is not None:
            return Verdict('READ-FAIL', res.error[0], res.error[1], None)
        if res.first_bad is not None:
            off, state, src = res.first_bad
            out('  [{:>9.2f} MiB written]  verified {:9.2f} MiB good, CORRUPTION FOUND'.format(
                tester.written / MIB, good / MIB))
            return Verdict('FAKE', off, note if not ok else None, (state, src, res.counts, res.runs))
        if not ok:
            out('  [{:>9.2f} MiB] {}'.format(tester.written / MIB, note))
            return Verdict('WRITE-FAIL', tester.written, note, None)
        out('  [{:>9.2f} MiB written @ {:>10}]  verified {:9.2f} MiB good  ({:.1f} MB/s read)'.format(
            tester.written / MIB, note, good / MIB, res.read_mbps))
        if first and tester.written < cap:
            est = estimate_seconds(cap - tester.written, wrate, res.read_mbps * 1e6)
            out('  (at these speeds the rest of the test takes roughly %s if the drive is genuine)'
                % fmt_duration(est))
            first = False
        stage *= 2
    return Verdict('PASS', tester.written, None, None)