Email Syntax Checker
Check an email address against RFC syntax rules one by one: @ count, local and domain length, dot placement, allowed characters and TLD. Free, instant, no DNS.
Check email syntax
Enter an email address for a rule-by-rule RFC syntax breakdown. No DNS lookup — format only.
What this syntax checker does
Common use cases
- 1Debugging why an address is rejected
- 2Learning the rules of valid email syntax
- 3Validating input in a form or script
- 4Checking a single address quickly
- 5Teaching correct email formatting
- 6Spotting illegal characters in an address
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About email syntax
Email address syntax is defined by RFC 5321/5322: a local part, an @, and a domain. The local part may use letters, digits and a set of special characters, must be 64 characters or fewer, and cannot start, end or run consecutive dots. The domain must be a valid hostname ending in a real top-level domain.
This checker applies those rules one by one so you can see exactly why an address is or is not well-formed. Remember that valid syntax is necessary but not sufficient — [email protected] is perfectly formatted yet undeliverable — so pair it with a live MX and mailbox check before relying on an address.
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Got Questions? We Have Answers.
What does the syntax checker validate?
It applies the RFC rules individually — exactly one @, local and domain length limits, no leading/trailing/consecutive dots, only permitted characters, and a valid top-level domain — and shows each as a pass or fail.
Does it check if the address exists?
No. It checks format only, with no DNS or mailbox lookup. A syntactically valid address can still be undeliverable — use the Email Address Validator for live MX and risk checks.
How long can a local part be?
The part before the @ may be up to 64 characters, and the whole domain up to 255. The checker flags anything over these limits.
Which characters are allowed before the @?
Letters, digits and a defined set of specials (such as . ! # $ % & ' * + / = ? ^ _ ` { | } ~ -). Other characters are only valid inside quotes, which is rare.
Why does my address fail on the dots?
A local part cannot start or end with a dot or contain two dots in a row (e.g. john..doe@). The checker highlights this specific rule.
Is anything sent to a server?
No. The check runs entirely in your browser with no network requests.