Receipt number format
Three letters such as SRC, LIN or IOE, then ten digits. It appears on Form I-797 notices, not on your visa or passport stamp.
Use the official checker at egov.uscis.gov
The real tool is plain, free and asks for one thing.
Type your receipt number, three letters followed by ten digits, into the checker at egov.uscis.gov and you get the latest action on the case: received, under review, evidence requested or decided. The tool never asks for your passport, social security number or card details, and it never charges. You can also open a free myUSCIS account to receive updates by email or text. If a page demands payment or identity documents to reveal a status, you are not on a government site.
Status messages matter
A phrase like 'request for evidence mailed' carries a deadline. Read the linked notice promptly, because response windows often run only weeks.
Recognize the lookalike status sites
Imitators buy ads and copy government styling to intercept anxious applicants.
Fraudulent checkers typically charge for 'expedited' results, request scans of passports or green cards, or promise contact with an officer. None of that exists in the real tool. Check the address bar for .gov, navigate from uscis.gov rather than from a search ad, and never send your receipt number to a stranger, since the number combined with basic personal data can be misused. When a site promises answers faster than the official estimate, it is selling something, and it is usually your data.