£1.00 per run, in pounds sterling. A card issued elsewhere pays the equivalent, converted by its issuer — about $1.20.
Your card is authorised when you submit: the amount is reserved, not taken. We take it only when your result is ready. If the run fails, times out, or is stopped for any reason, we cancel the authorisation — no charge appears on your statement, and there is nothing to refund.
Once a result exists, the work has been done and the £1 stands, including when the score disappoints you. Every run is a fresh run: uploading the same file again grades it again and costs £1 again.
We take cards through Stripe Checkout. Wallets are not offered because they cannot hold an authorisation without taking the money.