Regex for base64

Note

Checks the alphabet and padding. Plenty of ordinary words are valid Base64 too, so a match is not proof.

Matches in the example

• "aGVsbG8="
• "SGVsbG8sIHdvcmxkIQ=="

Token by token

1. ^ the start of the string (or line, with the m flag)
2. (?: a group, not capturing
3. [A-Za-z0-9+/]{4} one of: “A” to “Z”, “a” to “z”, “0” to “9”, “+” or “/”, exactly 4 times
4. )* end of group, whole group zero or more times, as many as possible
5. (?: a group, not capturing
6. [A-Za-z0-9+/]{2} one of: “A” to “Z”, “a” to “z”, “0” to “9”, “+” or “/”, exactly 2 times
7. == the text “==”
8. | or
9. [A-Za-z0-9+/]{3} one of: “A” to “Z”, “a” to “z”, “0” to “9”, “+” or “/”, exactly 3 times
10. = the character “=”
11. )? end of group, whole group optionally
12. $ the end of the string (or line, with the m flag)

Other patterns

• Email address
• URL
• IPv4 address
• UUID
• Hex color
• Date (YYYY-MM-DD)
• Time (24-hour)
• US phone number
• Phone number (E.164)
• US ZIP code
• Credit card number
• URL slug
• Username
• Strong password
• HTML tag
• Semantic version
• MAC address
• JSON Web Token
• Hashtag
• @mention
• Number
• Leading and trailing whitespace
• Repeated word
• Blank lines
• Markdown link
• Quoted string
• Domain name
• File extension
• Base64
• Trailing comma