Every cross-listing tool eventually has to explain its browser extension, usually while the person asking is deciding whether to trust it. Here is the honest version.
eBay has an API. The others do not.
eBay publishes a real REST API, so Arck talks to it from a server: no browser, no extension, works while you sleep. Depop, Grailed, Poshmark and Vinted publish nothing comparable. There is no endpoint to POST a listing to.
That leaves exactly one honest option: fill in the form the way you would, in your own browser, in your own signed-in session. That is what the extension does.
Why it is deliberately slow
A publish takes a minute or two per platform, and it is paced on purpose. Marketplaces watch for automation, and the cost of being wrong is not a failed upload. It is a restricted account and days of your selling time.
- Steps wait for the page to actually be ready, not for a fixed timer.
- Timing carries natural variation rather than machine-perfect intervals.
- Vinted runs on a slower schedule again, and is opt-in for that reason.
We do not offer a faster mode. There is no version of this where shaving twenty seconds is worth a suspended account.
What it can and cannot see
The extension works on the marketplace tabs it needs and nothing else. It has no reason to touch the rest of your browsing, and it does not.