Regex for Date Format Validation
Quick Answer: ISO 8601 date regex: ^\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])$. US format: ^(?:0[1-9]|1[0-2])/(?:0[1-9]|[12]\d|3[01])/\d{4}$. Note: regex validates format only, not calendar validity (it would accept Feb 30). Use date parsing libraries for full validation.
FAQ
Can regex check if a date is valid?
Regex can check format but cannot validate calendar rules (February 30, leap years). After regex format check, parse with a Date library for actual validation.
What date format should my API accept?
Use ISO 8601 (YYYY-MM-DD) for APIs. It is unambiguous (unlike MM/DD vs DD/MM), sorts lexicographically, and is the JSON and international standard.