Your Bluetooth USB tester on a full-screen dashboard, right in the browser. No app to install, no account, no ads.
Cheap USB testers like the J7-C and the ATorch UD18 measure well, but their phone apps are slow to pair, full of ads or no longer updated. USB Meter Web reads the same Bluetooth stream straight from the meter and shows everything it sends, all at once.
- Every reading at a glance. Voltage, current and power each get a large readout and their own graph. Temperature and the USB data lines (D+/D−) sit below, next to capacity, energy and elapsed time.
- One time axis. Point at any graph and a cursor reads out every value at that moment, so you can see what the voltage did when the current jumped.
- Min, average and max of voltage, current, power and temperature for the last minute, 10 minutes, hour or the whole recording.
- CSV export. Download the recording and keep working on it in a spreadsheet or a script.
- Ready for AI analysis. Export for AI packs the recording into a ZIP with a README that tells Claude, ChatGPT or any other assistant what you measured, what every column means and how to analyse it. You ask the question; the explaining is done.
- A device list without the clutter. The Bluetooth list shows meters, not your keyboard, mouse and earbuds.
- Private by design. Readings stay in your browser and are never sent anywhere. No cookies, no analytics.
- Desk or pocket. The dashboard fills a monitor and stacks into one column on a phone, in light or dark.
- In your language. English, Deutsch, Español, Français, Italiano, Português (Brasil), Русский, 日本語, 한국어, 简体中文 and 繁體中文. The page starts in the language your browser asks for and has a list for choosing another.
- No meter at hand? Try the demo plays a pretend charger so you can look around first.
- Open usbmeter.koeda.me in Chrome or Edge.
- Plug the meter between a charger and the device you want to measure. If it was plugged in already, unplug it and plug it back in.
- Choose Connect to meter straight away and pick the meter in the browser's Bluetooth list.
A J7-C shows up as
UC96_BLE, ATorch meters under their model name (UD18-BLE,AT24-BLE, ...). Readings start at once.
Meter not in the list? Unplug it, plug it back in and choose Connect to meter again straight away. Some meters, the J7-C among them, can only be found shortly after they get power, so one that has been on for a while stays out of the list. The page says so next to the button, too.
If that does not help: a meter is listed only while the browser can hear it, so it needs to be nearby, with its Bluetooth switched on and no other connection, because these meters talk to one device at a time. Close the phone app first. Still missing? Cancel the list and choose Show all Bluetooth devices. When the page does not know the name of a meter connected that way, it says so; please open an issue with that name so it can be added.
A recording can answer questions such as how long did the charge take, and when did it start to taper?, does this charger hold its voltage?, how much does this power bank really deliver? or what does my project draw on average? An AI assistant can work that out, provided it knows what it is looking at. Export for AI takes care of that:
- Record, then choose Export for AI.
- Pick what you measured: charging a device, a charger or power supply, a power bank or battery, a cable, the power draw of a device, or an appliance on an AC meter. Add a note if you like, such as "65 W charger, 1 m cable, phone starting at 20 %".
- Give the downloaded ZIP to Claude, ChatGPT or another assistant and ask your question. If it does not take ZIP files, unpack it and give it both files. The README in the ZIP is written in English whatever language the page is in; ask in your own language and the assistant answers in it.
The ZIP holds two files:
readings.csv: the readings, the same file Download CSV gives.README.md: the meter, the time span, your purpose and notes, and a summary (the range of every reading, energy and charge totals, pauses in the recording). Then a guide for the assistant: what each column means, what a meter like this can and cannot measure, how to read the USB data lines, and what to work out for your kind of test.
The page still sends nothing anywhere. The ZIP goes only where you put it.
The guide is also a Claude skill. With the skill added, Claude has the guide at hand even when it gets only the CSV.
- Claude: on the page, under Help, choose Download the Claude skill and add that ZIP as a skill (how to add a skill).
- Claude Code: copy the folder
skills/usbmeter-analysisinto~/.claude/skills/.
| Meter | Type | Status |
|---|---|---|
| J7-C | USB | Checked against frames recorded from a real J7-C (values match its screen) |
| ATorch UD18 and similar | USB | Checked against published sample packets |
| ATorch AC meters (AT24, AT3010) | AC | Checked against published sample packets. Adds frequency and power factor |
| ATorch DC meters (DT24, DT3010) and others with the same protocol | DC | Experimental: voltage, current, power, temperature and time. Capacity and energy are not decoded yet, because the published layouts disagree |
The type (USB, DC or AC) is read from the data, so a model that is not listed may still work. If your meter connects but shows nothing, please open an issue with its name and model.
The page uses Web Bluetooth, which Chrome and Edge provide on Windows, macOS, ChromeOS and
Android. On Linux, Chrome keeps it switched off until you enable
chrome://flags/#enable-experimental-web-platform-features. Firefox and Safari do not support
it, and neither do browsers on iPhone and iPad (except apps that add it, such as Bluefy). The
demo works everywhere.
Everything runs in your browser. Readings are kept in memory while the page is open and are
never sent anywhere. There are no cookies, no analytics and no ads, and the page stores nothing
in your browser: the language you choose is kept in the address (?lang=). The site's headers
forbid scripts from, and connections to, any other origin, and a test pins them
(public/_headers, src/security-headers.test.ts).
Like any website, the page is delivered by a hosting provider, which sees your IP address when you load it.
- Who runs it: koedame, an individual. Questions and bug reports go to the issues, security problems to SECURITY.md.
- No warranty: the page is provided as is, under the MIT License. Readings can be wrong. It is not a calibrated instrument and not a safety device: do not use it to decide whether a circuit, a charger or an appliance is safe.
The meters stream their readings from a serial-over-Bluetooth characteristic (service 0xFFE0,
characteristic 0xFFE1). Every frame is FF 55 <type> <payload> <checksum>. A report (type
01, 36 bytes) carries the device type (01 AC, 02 DC, 03 USB) and big-endian readings. The
ATorch checksum is the sum of the bytes between the header and the checksum, xor 0x44. The
J7-C uses a different checksum whose formula is unknown, so its frames are accepted without
checksum verification when they are otherwise well formed.
The layout is based on community notes (esphome-atorch-dl24, atorch-console) and on the J7-C capture in this forum thread. Capacity is read as mAh (value ÷ 1000 Ah); the UD18 sample packets are consistent with that.
Bug reports, meter names and captures from meters that are not listed are all welcome. CONTRIBUTING.md explains how to run the page locally and how it is tested without a meter. It is plain TypeScript with no runtime dependencies.
Bluetooth 対応の USB テスター（J7-C・ATorch UD18・AT24 など）の値を、ブラウザのダッシュボードで 見るためのページです。アプリのインストールもアカウントも要りません。画面は日本語で表示されます （ブラウザの言語に合わせて選ばれ、右上の一覧から変えられます）。
- 電圧・電流・電力を大きな数字とグラフで同時に表示。温度と D+/D− もその下に並びます
- グラフは全部同じ時間軸。どれかにポインタを置くと、その瞬間の全部の値が出ます
- 表示している範囲（1 分・10 分・1 時間・全部）の最小・平均・最大
- 記録は CSV で保存できます
- 「AI 用にエクスポート」は、記録の CSV と、測ったもの・各列の意味・分析の進め方を書いた README を
1 つの ZIP にします。Claude や ChatGPT に渡して日本語で質問すれば、説明なしで分析が始まります
（README は英語で書かれています）。同じ内容の Claude 用スキルも
skills/usbmeter-analysisにあります - Bluetooth の一覧にはメーターだけが並びます
- 値はブラウザの中だけで扱い、どこにも送りません
使い方:
- Chrome か Edge（Windows・macOS・ChromeOS・Android。Linux の Chrome は、先に
chrome://flags/#enable-experimental-web-platform-featuresを有効にします）で usbmeter.koeda.me を開きます。 - メーターを充電器と測りたい機器の間に挿します。挿したままだったときは、一度抜いて挿し直します。
- すぐに「メーターに接続」を押して、一覧からメーターを選びます。J7-C は
UC96_BLEという名前で出ます。
一覧にメーターが出ないときは、メーターを抜いて挿し直し、すぐにもう一度「メーターに接続」を押してください。 J7-C など、電源が入った直後しか見つからないメーターがあります。
iPhone・iPad の Safari は Web Bluetooth に対応していません。メーターが手元に無くても、「デモを試す」で画面を試せます。
MIT. Not affiliated with ATorch, any meter maker or any AI provider; product names belong to their owners.