# Check if a string contains only ASCII characters

Test that every character is in the 0–127 range.

Canonical: https://1loc.dev/validator/check-if-a-string-contains-only-ascii-characters/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function isAscii(text) { return /^[\x00-\x7F]+$/.test(text); }
```

## Input

```json
"ana@example.com"
```

## Expected output

```json
true
```

## Edge case

Input:
```json
"ana@bücher.example"
```
Output:
```json
false
```

## Limits

- The empty string fails.
- Oveyon refuses non-ASCII addresses with address_not_ascii; convert an international domain to punycode first (see the email collection).

The lab validates types and size before calling this function. Add equivalent validation at your own trust boundary.

## Source and license

Original: https://github.com/phuocng/1loc/blob/14b481cf60dff1620ab1bb99a43b1f68068cdd9b/contents/check-if-a-string-contains-only-ascii-characters.mdx
Author: Nguyen Huu Phuoc and original contributors
Contributors: See original repository history
Source commit: 14b481cf60dff1620ab1bb99a43b1f68068cdd9b
Copyright (c) 2020 phuoc-ng
License: MIT — https://1loc.dev/licenses/
Maintainer: Oveyon
Modifications: Curated implementation; explicit input contract, edge case and limits. Original MDX retained as inert source evidence.