The IRS has ‘transcripts’ with a listing of the information filed with them. This usually includes information such as W-2s, 1099s, 1098s, IRA distributions, 1099-DIVs, and 1099-INTs. Since the IRS needs to first receive these documents from your employer or bank, they are often not available for you to review until after the regular deadline. In the case that you need this information to file, you should file an extension and then pull your IRS transcripts to use the information to file your tax return.
Keep in mind that this transcript won’t include some additional information that may help you reduce your tax liability, such as deductions like employee business expenses, home office expenses, charitable contributions, or tax preparation fees. There are many more items you may need to report on your tax return, but looking at your IRS transcript gives you a good baseline (and often prevents you from getting issued an automatic notice from the IRS)