Most pre-launch checklists have 200 items and nobody finishes them. This one has 22. They are ordered by what costs you money when it fails, not by what is easy to check.
Work down the list. Stop when you run out of time. You will have covered the expensive failures first.
Money paths — do these first
These are the paths where a bug costs you revenue on the day it ships.
1. Complete a purchase or signup with a real card or real details. All the way through. Not a test card in a sandbox — the live path, once, before you announce anything.
2. Try to pay with a card that will decline. Most payment providers publish test card numbers that force a decline. Your site should tell the customer clearly what happened and let them try again. 42% of consumers say they would never return to a site after one wrongly declined payment.
3. Try to pay with an expired card. Stripe found 45% of checkouts in APAC allowed a customer to attempt payment with an expired card. The failure appears later, confusingly, and the customer blames you.
4. Enter an invalid card number. More than one in three European checkouts accept one, per the same research.
5. Close the browser tab mid-payment, then go back. Look at what state the basket and the order are in. This is where duplicate charges and orphaned orders come from.
6. Confirm the confirmation email arrives. Check the subject line, the sender name, and that no field says "undefined" or "null". Check it in Gmail and in one other client.
7. Apply a discount code. Then apply an invalid one. Then apply the valid one twice.
Forms — the second most expensive area
8. Submit every form with all fields empty. You should get clear errors, not a blank page.
9. Submit a form with one field wrong. Everything the user already typed must still be there afterwards. A form that clears itself on a validation error is one of the most reliable ways to lose a customer.
10. Enter an email address without an @ symbol.
11. Paste a very long string into a text field. 500 characters. Look for layout that breaks.
12. Submit a form twice quickly. Check you do not get two records.
Mobile — over half your traffic
13. Open the site on a real phone, not just a resized browser window. Resizing does not reproduce touch targets, on-screen keyboards, or scroll behaviour.
14. Check the main action button is visible without scrolling.
15. Open every form on the phone and check the keyboard does not cover the field you are typing in.
16. Rotate the phone to landscape on your most important page.
Content and trust
17. Click every link in the navigation and footer. Include the ones nobody clicks — privacy policy, terms.
18. Check for placeholder text. Search the live site for "Lorem", "TODO", "test", and "example.com".
19. Check the page titles in the browser tab. Not one of them should say "Home" or "Untitled".
20. Share one link on a messaging app. Look at the preview card. A missing preview image makes a real business look abandoned.
Speed and errors
21. Load your slowest page on a phone on mobile data, not wifi. 53% of mobile visits are abandoned if a page takes longer than three seconds.
22. Open the browser console on your three most important pages. Red errors mean something is broken, even if the page looks fine.
What this checklist does not cover
It covers the common, expensive failures. It does not cover your product's own logic — the thing that makes your product yours. Nobody can write a generic checklist for that, which is the honest limit of any list like this one.
It also assumes you are testing what you built. You will unconsciously avoid the paths you know are fragile. That is not a character flaw; it is how everyone tests their own work.
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