Directly from the IRS:
Contributions not reported. You do not report Roth IRA contributions on your return.
If that's the case, then how does the IRS make sure people don't exploit the system? (E.g. having multiple Roth IRA accounts with different brokerages and maxing them all out every year).
I feel like my knowledge of the tax system is so limited that I'm missing something super obvious. What am I missing?