Regex for an email address

Answer

Use ^[^\s@]+@[^\s@]+\.[^\s@]+$: one or more non-space, non-@ characters, an @, then a domain with at least one dot. It catches typos like a missing @ or a stray space. Then prove the address works by sending a confirmation email.

JavaScript ✓PCRE ✓

Slow on long input. [^\s@]+ and [^\s@]+ can match the same characters, and what lies between them can be matched by the first one too. On a long string that fails to match, the engine tries every split point: quadratic time. Harmless on short input, a risk on long untrusted input. Make the first part unable to match what follows it (for example [^.@]+ instead of [^@]+ before \.), or limit the input length before matching.

^Start of the stringanchor
[^\s@]Any one character except a whitespace character (space, tab, line break and other Unicode spaces) and '@'character class
+Repeat the class one or more times, as many as possible (greedy)quantifier
@The character '@' literallyliteral
[^\s@]Any one character except a whitespace character (space, tab, line break and other Unicode spaces) and '@'character class
+Repeat the class one or more times, as many as possible (greedy)quantifier
\.The character '.' literallyliteral
[^\s@]Any one character except a whitespace character (space, tab, line break and other Unicode spaces) and '@'character class
+Repeat the class one or more times, as many as possible (greedy)quantifier
$End of the stringanchor

Examples

Checked at build time in JavaScript and in Python's re.

Input	Matches?
`user@example.com`	✓ match
`first.last+tag@sub.example.co.uk`	✓ match
`o'brien@example.ie`	✓ match
`no-at-sign.example.com`	✗ no match
`user@localhost`	✗ no match
`two words@example.com`	✗ no match
`user@@example.com`	✗ no match
`a@b.c`	✓ match
`user@example..com`	✓ match
`user@.example.com`	✓ match

Try your own text

One string per line: each line is tested on its own (the m flag is added here).

How it works

The full grammar in RFC 5322 allows quoted local parts ("john doe"@example.com), comments in parentheses, and IP-literal domains (user@[192.0.2.1]). A regex that covers all of it runs to thousands of characters, and it still cannot tell you whether a mailbox exists. The only real test is a message the user receives and clicks.

So the job of the regex is a sanity check: reject input that is obviously not an address, and accept everything a real mail server might take. A pattern that is too strict is worse than one that is too loose. It turns away real customers with addresses like o'brien@example.ie or user+tag@example.com.

Browsers have their own check. An <input type="email"> validates against a pattern from the HTML standard (shown below under variants). It is deliberately simpler than RFC 5322: it does not allow quoted local parts, and it accepts a domain with no dot, such as user@localhost.

Variants

/^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/
The pattern the HTML standard specifies for <input type="email">. ASCII only, and it accepts user@localhost.
/^[^\s@]+@[^\s@]+$/
Looser still: anything with exactly one @ and no spaces. Use it when intranet hosts without a dot are valid.

Gotchas

This pattern accepts user@example..com and user@.example.com. Both are invalid domains. The confirmation email catches them; the regex does not try to.
It rejects user@localhost because it requires a dot after the @. That is right for a public sign-up form and wrong for an internal tool.
Do not lowercase the whole address before storing it. The domain is case-insensitive, but RFC 5321 lets the local part be case-sensitive. In practice almost no provider treats it that way, so compare case-insensitively but keep what the user typed.
Internationalized addresses such as 用户@例子.广告 are valid under RFC 6531. [^\s@] accepts them. Patterns built on [a-zA-Z0-9] do not.
Cap the length first (254 characters is the practical maximum for an address). The domain part [^\s@]+\.[^\s@]+ can match dots in many ways, so a long run of dots followed by a space takes quadratic time to reject.

Related explainers

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