isValidEmail

Validates whether a string is a well-formed email address. Uses the HTML5 living-standard email pattern (the same one browsers use for <input type="email">) plus RFC 5321 length limits (local part ≤64, total ≤254). Pragmatic over RFC 5322 strict — accepts the addresses people actually use.

Try it

Import

import { isValidEmail } from "1o1-utils";

import { isValidEmail } from "1o1-utils/is-valid-email";

Signature

function isValidEmail({ email, allowDisplayName }: IsValidEmailParams): boolean

Parameters

Name	Type	Required	Description
email	unknown	Yes	The value to validate
allowDisplayName	boolean	No	When true, also accepts display-name form like "Jane Doe <jane@example.com>" or '"Doe, Jane" <jane@example.com>'. Default false

Returns

boolean — true if the value is a parseable email, false otherwise.

Examples

isValidEmail({ email: "user@example.com" });           // => true
isValidEmail({ email: "user+tag@gmail.com" });         // => true
isValidEmail({ email: "first.last@sub.example.io" }); // => true

isValidEmail({ email: "invalid@" });                   // => false
isValidEmail({ email: "no-at-sign.com" });             // => false
isValidEmail({ email: "" });                           // => false
isValidEmail({ email: null });                         // => false

// Display-name form (opt-in)
isValidEmail({
  email: "Jane Doe <jane@example.com>",
  allowDisplayName: true,
}); // => true

isValidEmail({
  email: '"Doe, Jane" <jane@example.com>',
  allowDisplayName: true,
}); // => true

isValidEmail({
  email: "Jane Doe <jane@example.com>",
}); // => false (not allowed by default)

// Validate user input before sending
function subscribe(input: string) {
  if (!isValidEmail({ email: input })) {
    throw new Error("Invalid email");
  }
  return api.subscribe(input);
}

Edge Cases

• Non-string inputs (null, undefined, numbers, objects, arrays) return false.
• Empty strings return false without invoking the regex.
• Length-bounded: local part > 64 chars, total > 254 chars, or raw input > 320 chars returns false (the 320-char input cap blocks pathological payloads before any regex work).
• Hostname labels cannot start or end with a hyphen, and empty labels (example..com) are rejected.
• Whitespace and control characters anywhere in the address return false unless allowDisplayName is set and the wrapper itself contains whitespace.
• ASCII-only host part — internationalized domain names (IDN) such as user@münchen.de return false. Convert IDN hosts to Punycode (e.g., user@xn--mnchen-3ya.de) before validating.
• Consecutive, leading, or trailing dots in the local part (e.g., a..b@example.com, .user@example.com) are accepted — matches the HTML5 living standard. RFC 5322 strict disallows them; this validator favors HTML5 compatibility.
• The validator is structural — it does not perform DNS, MX, or SMTP checks.

Also known as

email, validate email, is email, valid email, email check, email validator

Prompt suggestion

I'm using 1o1-utils (npm: https://www.npmjs.com/package/1o1-utils, GitHub: https://github.com/pedrotroccoli/1o1-utils, LLM context: https://pedrotroccoli.github.io/1o1-utils/llms.txt). Show me how to use isValidEmail to validate a user-supplied email before submitting a form.