The page says "Thanks for applying". Maybe it shows a reference number. You close the tab, tick it off your list, and move to the next posting.
As far as you know, that application exists.
Sometimes it doesn't.
Who is actually telling you it worked
The confirmation screen is rendered by the page you were already on. It is your own browser reporting back on what your own browser just did. That's not nothing, but it's the weakest kind of evidence there is, because it can be true in every visible way and still be wrong underneath.
A file attachment that reported as uploaded but sent zero bytes. A required question below the fold that failed validation on a step you already passed. A session that expired between page four and page five. In each of those the screen can still look like success.
The only evidence that means anything comes from the other side. Something the employer's system produced, not something yours did.
The two checks, both free
Check one: the receipt email, within a few minutes. Greenhouse, Lever, Ashby and most modern applicant tracking systems fire an automatic acknowledgement almost immediately. If ten minutes pass and there's nothing, including in spam, treat that as a signal rather than as normal. Some employers genuinely disable the acknowledgement, so this is not proof of failure on its own. It's the first thing to look at.
Check two: the candidate portal. Workday, iCIMS, SuccessFactors and Taleo all make you create an account. That account has a page listing your applications. Log back in a day later and look. If the application is listed there, it exists in their system, and no confirmation screen is needed. If it isn't listed, you have your answer.
Do both and you know. Do neither and you're relying on a screen that was only ever describing itself.
What to do when one is missing
Don't immediately resubmit. Duplicate applications look careless and some systems reject the second one silently, which puts you right back where you started.
Instead: open the posting again in a fresh tab. If the ATS shows "you have already applied", it's in. If it shows you a blank form as though you'd never been there, that's the strongest signal you'll get that the first attempt didn't land, and now resubmitting is the right call.
Why I care about this so much
I work on AI Applyd. We build the thing that fills in employer forms and submits them, and the hardest part of that job was never the filling in. It was proving the application arrived.
So we stopped scoring our own work on what our own browser reported and started scoring it on what the employer's system sent back. The receipt, the portal entry, the request the other side actually accepted.
That's the standard I'd hold any tool to, including ours, and honestly including your own spreadsheet. A row that says "applied" is a record of your intention. A receipt is a record of theirs.
