Why Your Flash Drive or Keyboard Won't Show Up
This is the single most common point of confusion with any WebUSB device viewer online: WebUSB was designed for interactive hardware — 3D printers, microcontrollers (Arduino, ESP32), FIDO security keys, custom lab equipment — that expose a vendor-specific interface and want direct browser communication. Mass storage devices, HID devices (keyboards, mice, most game controllers), printers, and audio devices are already claimed by your OS's built-in class drivers, and browsers deliberately refuse to let a website steal that interface out from under the operating system. If you need a full inventory of every USB device on your machine, you want a native OS tool (covered in the comparison table below), not a browser tab.
Reading VID, PID, and Device Class
Every USB device advertises a Vendor ID (VID) and Product ID (PID) — a 16-bit hex pair assigned to the manufacturer and their specific product line, the same identifiers Windows Device Manager, macOS System Information, and Linux's lsusb use internally. The device class (and subclass) tells the host what kind of device it's talking to at the top level — for example class 0xFF means "vendor specific," while class 0x03 is Human Interface Device. A class of 0 means "look at the interface descriptors instead," which is common on composite devices that bundle several functions (e.g. a USB hub with a built-in card reader) into one physical device.
- Click "Request Device Access"Your browser opens its own native device picker — this tool never sees devices you don't explicitly choose.
- Pick your device from the listIf it doesn't appear, it's most likely claimed by an OS driver already (see above) rather than a bug in this tool.
- Review the descriptor gridVID/PID, USB spec version, device class/subclass, and serial number populate instantly from the device's own descriptors.
- Run "Test Connection"Attempts to actually open the device and claim its first interface, then releases it — a real functional check, not just a permissions list.
- Expand the configuration treeWalk down through configurations → interfaces → endpoints to see transfer types (control/bulk/interrupt/isochronous) and max packet sizes.
Understanding Configurations, Interfaces & Endpoints
A USB device exposes one or more configurations (almost always just one in practice); each configuration bundles one or more interfaces, and each interface bundles one or more endpoints — the actual communication channels, each with a direction (IN/OUT), a transfer type (control, bulk, interrupt, or isochronous), and a maximum packet size in bytes. This tree is exactly what a driver author or firmware developer needs to check when debugging a custom USB device, and it's normally only visible through native tools like lsusb -v or Windows' USBView — seeing it directly in a browser tab is what makes a USB descriptor viewer online like this genuinely useful for quick checks.
What "Test Connection" Actually Checks — and Why It Sometimes Fails
Listing a device's descriptors doesn't prove your browser can actually talk to it. The Test Connection feature calls the real WebUSB session lifecycle — open(), selectConfiguration(), claimInterface(), then immediately releaseInterface() and close() again — and reports exactly what happened. A failure here almost always means the interface is already claimed by an OS driver (extremely common on HID-class and composite devices), not that anything is broken. Pure vendor-specific hardware (Arduino running a custom firmware, most 3D printer boards, FIDO keys in certain modes) typically passes cleanly.
| Tool | Strength | Where It Falls Short |
|---|---|---|
| lsusb / lsusb -v (Linux) | Complete kernel-level device tree, no picker dialog needed | Terminal only, Linux-only, no live connection test |
| USBView (Microsoft, Windows) | Deep low-level descriptor view, sees every USB device on the bus | Windows-only, separate signed download, dated interface |
| System Information (macOS) | Built into macOS, sees all connected USB hardware | Apple-only, no endpoint-level or configuration tree detail |
| chrome://usb-internals | Chrome-native low-level USB event log | Developer-facing, not user friendly, Chrome only |
| PC Tester WebUSB Inspector | Instant, cross-platform, full descriptor tree plus a live connection test, zero install | Only sees devices you explicitly authorize with vendor-specific interfaces — by design, not a bug |
navigator.usb running inside your own browser tab. Nothing about your device, its descriptors, or its serial number is sent to any server — the exported report is generated and downloaded entirely client-side.Frequently Asked Questions
Why can't I see my USB flash drive, keyboard, or mouse in this tool?
WebUSB deliberately can't access devices already claimed by your OS's built-in drivers — mass storage, HID (keyboards/mice/most controllers), printers, and audio devices fall into this category. This is a browser security boundary, not a bug, and it applies to every website, not just this one.
What do VID and PID actually mean?
Vendor ID and Product ID are a 16-bit hex pair every USB device reports: the VID identifies the manufacturer (assigned by usb.org), and the PID identifies that manufacturer's specific product. Together they're how your OS picks which driver to load.
What does "SecurityError" or "NotFoundError" mean when I click Request Device Access?
NotFoundError usually just means you closed the picker dialog without choosing a device. SecurityError means the current page context is blocked from using WebUSB — most often because the page isn't served over HTTPS (or localhost) or is loaded inside a restricted iframe.
Is my USB device's data uploaded anywhere?
No. All descriptor reading and the connection test run entirely inside your browser via the standard navigator.usb API. Nothing leaves your device, and the exported report is written straight to a local file using your browser's download mechanism.
Why does "Test Connection" fail for some devices?
Almost always because the interface is already claimed by an operating system driver — common on HID-class and composite devices. Pure vendor-specific hardware (custom firmware on an Arduino or ESP32, for example) usually passes without issue.
Can this replace lsusb, USBView, or System Information?
Not fully — those native tools can see every USB device on the bus, including ones claimed by OS drivers. This tool's advantage is that it needs zero installation and works cross-platform in any Chromium browser, but it's scoped to devices you explicitly authorize.
Do I need a special browser?
You need a Chromium-based browser — Chrome, Edge, Brave, Opera, or Vivaldi — served over HTTPS (or localhost). Firefox and Safari have not implemented the WebUSB specification.
What is a USB configuration, interface, and endpoint?
A configuration is the top-level bundle a device offers (almost always just one). Each configuration contains one or more interfaces (distinct functions), and each interface contains one or more endpoints — the actual data channels, each with a direction and transfer type.
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Written by Adeel Farooq, Founder of PC Tester — 50+ browser-based diagnostic tools built, working in PC hardware diagnostics since 2013. See our Privacy Policy and Disclaimer.