Email Validation — The Sane Default

The 99% pattern

Real email regex (RFC 5322 compliant) is over 6,000 characters and includes nested comments, quoted strings, IP literals, and Unicode. Don't try to write it. The sane production default is:

^[\w.+-]+@[\w-]+\.[\w.-]+$

Reading left to right:

[\w.+-]+ — local part: word characters plus . + -
@ — literal at-sign
[\w-]+ — domain label (no dots inside)
\. — literal dot
[\w.-]+ — TLD with allowed subdomains and hyphens

What this catches

Typos: missing @, missing TLD, spaces in addresses, completely invalid shapes. About 95% of "is this an email?" use cases.

What it MISSES (and why that's fine)

Quoted local parts: "hello world"@example.com — valid per spec, almost never used.
IP-literal domains: user@[192.168.1.1] — same.
Non-ASCII Unicode local parts: 유저@한국.kr — needs Unicode flag and adjusted character classes.
Whether the email actually exists.

For real "does this email work?" — send a verification message. Regex can't tell you that.

The HTML5 alternative

Browsers' built-in type="email" validation uses a slightly more permissive regex. If you're in a browser, just use it: <input type="email" required>. Saves you the regex entirely.

Code

Email validation·python

import re

EMAIL = re.compile(r'^[\w.+-]+@[\w-]+\.[\w.-]+$')

# Tests
bool(EMAIL.fullmatch('hi@example.com'))         # True
bool(EMAIL.fullmatch('hi+tag@example.co.kr'))   # True
bool(EMAIL.fullmatch('user.name@sub.domain.org'))  # True

# Catches
bool(EMAIL.fullmatch('no-at-sign'))             # False
bool(EMAIL.fullmatch('@no-local'))              # False
bool(EMAIL.fullmatch('hi@example'))             # False (no TLD)
bool(EMAIL.fullmatch('hi @example.com'))        # False (space)

# Find emails in text (no anchoring)
EMAIL_FIND = re.compile(r'[\w.+-]+@[\w-]+\.[\w.-]+')
re.findall(EMAIL_FIND, 'reach me at hi@pippa.dev or admin@cwk.io')
# ['hi@pippa.dev', 'admin@cwk.io']

Email Validation — The Sane Default

The 99% pattern

What this catches

What it MISSES (and why that's fine)

The HTML5 alternative

Code

External links

Exercise

Progress

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