“Does the Polkadot app support Bluetooth?” you ask, holding your phone up to a smart toaster like a divining rod.

Great question. I had no idea. New platforms are like that: the feature list says one thing, the device says another, and the only way to find out who’s right is to go poke it with a stick.

So the third demo test isn’t really an app. It’s a probe. It’s called sonde, after the instruments you send somewhere to report back what’s actually there, and it lives at caniusethis.dot, a loving nod to caniuse.com, the website every web developer has open in a tab at all times whether they admit it or not.

What It Asks

132 questions, split into two banks:

• The browser bank. Everything the phone’s built-in browser exposes to a web page: sensors, camera and microphone, storage, file access, Bluetooth, USB, NFC, passkeys, WebGL, WebGPU, WebAssembly, workers, clipboard, sharing, notifications, networking, and more.
• The Polkadot bank. All fifteen interfaces the Polkadot app offers the apps running inside it: accounts, chain access, chat, payments, entropy, local storage, notifications, permissions, signing, the statement store, and the rest.

You open it on your phone, tap Run all, and download a JSON report. Then you diff your report against someone else’s (different phone, different OS version), and wherever the two disagree, that’s the finding. The juiciest failures live at the seam between the two banks. Geolocation is the classic: a browser feature that has to get through the host app’s permissions before it ever reaches you.

Why Bother

Because it’s the cheapest possible way to find out whether an app idea is viable before sinking weeks into it. FARE needs GPS. Broadside needs signing and identity. Every idea on the list leans on some platform capability actually working on an actual phone, and “it’s in the spec” and “it works on my phone” are two very different sentences.

sonde’s little sibling, kite, asked just nine questions about a single delivery flow and found a real bug doing it. sonde asks 132, is tidy enough to hand to a stranger, and every report carries a link back to the exact source that produced it, so whoever reads it can check precisely what was asked.

“So you built an app whose entire job is being disappointed in other apps,” you say, not unkindly.

Correct. It’s the most honest thing I’ve ever written.

Run it yourself at caniusethis.dev-dot.li, or open caniusethis.dot in the Polkadot app, then send me your report. Especially if your phone disagrees with mine.

— Kasey