What is sent, and what is not
Every host this site talks to, and what each request carries. It is written so that you can decide whether the site is usable where uploading to an outside service is not allowed — from facts rather than from our reassurance.
Never sent
Nothing you hand to a tool leaves your device, with the two exceptions below. All processing happens inside your browser.
- Audio and video files, and the results of separating or converting them
- Image files, including the capture date, camera model and GPS position inside them
- PDFs and the text inside them
- Text you paste into a field (address lists, JSON, API responses)
- File names
- Microphone audio (tuner, voice recorder)
Two exceptions — in both cases, that is what the tool is for
- The domain you type into DNS Lookup goes to Cloudflare’s public DNS (cloudflare-dns.com). The names live out there, so there is no way to resolve one without sending it. Note that an internal-only hostname would leave your network.
- A file you send with device-to-device transfer arrives on the device you picked — that is the point of the tool. It travels straight between the two devices and never lands on this site’s server; only the information needed to open the connection (SDP and ICE candidates) passes through it.
Hosts the page does contact
The page itself does talk to the following. These are what appear in a browser network tab — and apart from the two exceptions above, none of them carries your files or text.
| Host | Purpose | When it happens |
|---|---|---|
pagead2.googlesyndication.com / googleads.g.doubleclick.net | Ads (Google AdSense). This is what pays for running the site. | Always. Uses cookies. |
www.googletagmanager.com | Analytics (Google Analytics 4) — which pages get used. | Only when an analytics ID is configured. Uses cookies. |
/_vercel/insights | Page-view counting (Vercel Analytics). Same domain as the site. | Always. |
fonts.googleapis.com / fonts.gstatic.com | The Japanese typeface (Noto Sans JP). | On Windows. Not on macOS, iOS or Android, where a face already on the device is used. |
huggingface.co | The AI separation model weights. Once fetched they are stored on the device and not requested again. | Only when you run a separation. |
www.jma.go.jp / www.data.jma.go.jp | Weather forecasts and earthquake reports (Japan Meteorological Agency open data). Only which region or list you viewed is sent. It does not pass through this site’s server. | On opening the weather tool. The earthquake tool checks for new reports every 90 seconds while it is open (it stops when the tab is hidden), and fetches the past list only when you press load. |
speed.cloudflare.com | Runs the connection speed test. Only filler data is exchanged to time the transfer — no files and no input. It does not pass through this site’s server. | Only when you press Measure in the speed test. Up to 21MB down and 6MB up per run. |
cloudflare-dns.com | DNS-over-HTTPS queries for the DNS lookup tool. The domain you type is sent there. It does not pass through this site’s server. | Only when you press Look up in the DNS lookup tool. |
/api/ip | Powers the IP address check. Same domain as the site; no third-party IP service is involved. The address is used to build the response and is not stored. | Only when the IP address check page is open. |
stun.l.google.com | STUN for NAT traversal (WebRTC) — asking what your address looks like from outside. Your public IP is visible to that Google server while this happens. No file data passes through it. | Only while a device-to-device transfer is establishing a connection. |
stemstudio-beam.stemstudio-jp.workers.dev (our server) | Two uses. First, device-to-device transfer: the information needed to find the other device and open a connection (SDP and ICE candidates) — the file itself goes straight between devices and never passes through it. Second, submitting a result to a game ranking: your name and the sequence of moves you played. A score is never accepted; the move count is recomputed from that sequence on the other end. | When you use device-to-device transfer, and when you press Submit on a game ranking yourself. |
nzf358i1c3wxy8sd.public.blob.vercel-storage.com (Vercel Blob — our distribution store) | The desktop installer (.msi) itself. Only a file we send you; none of your files or input goes there. | Only when you open the desktop download page (which starts the download as soon as it opens). The audio, image and PDF tools never talk to it. |
How to check for yourself
You do not have to take our word for it. Either of these settles it.
- Use a tool with the network tab open. The requests in the table above appear; no file upload does.
- Use a tool once, then switch the network off (airplane mode). The same tool keeps working — which is what shows the processing needs no network.
Limits worth stating
- Ads and analytics use cookies and pass information to Google services. Where that is unacceptable, blocking those domains with an extension or a corporate filter does not affect how the tools work — you simply see no ads.
- This site is run by one person. There is no SLA and no audit report. What you have to go on is the table above and the behaviour you can verify yourself.
- Device-to-device transfer is the one tool that does send a file to another device. It differs in kind from the rest; treat it separately.
For personal data, see theprivacy policy.