Add Vietnamese Accents Online

Restore Vietnamese diacritics in text typed without accents (“xin chao cac ban” → “xin chào các bạn”) using a dictionary and syllable frequencies.

Result

Press “Run” to see the result.

The accent restoration API turns Vietnamese typed without diacritics, common in SMS, chats, old databases and product names, back into proper Vietnamese: Ngan hang Nha nuoc vua giam lai suat → Ngân hàng Nhà nước vừa giảm lãi suất. Each run of unaccented words is solved as a whole with dynamic programming: the API prefers sequences that form dictionary words of two to four syllables, then the most frequent syllables.

Capitalisation is kept (Ha Noi → Hà Nội, CONG TY → CÔNG TY), punctuation and numbers are left alone, and words that are not Vietnamese stay unchanged. alternatives=1–5 lists, for every ambiguous syllable, the other likely readings, so an interface can let the user pick (ban: bạn / bán / bàn).

It runs on a word list and frequency tables, without an AI model, in a few milliseconds. Results are good for common phrases and names; short or unusual sentences can need a human check. Text that is already partly accented is fine: syllables typed with accents are kept as they are and help choose the accents of their neighbours.

Use this in your code

curl -X POST "https://apibox.io.vn/v1/vn-diacritics" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"text":"Ngan hang Nha nuoc vua giam lai suat dieu hanh","alternatives":2}'

const res = await fetch('https://apibox.io.vn/v1/vn-diacritics', {
  method: 'POST',
  headers: {
    Authorization: 'Bearer YOUR_API_KEY',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    "text": "Ngan hang Nha nuoc vua giam lai suat dieu hanh",
    "alternatives": 2
  }),
});
const data = await res.json();
console.log(data);

import requests

res = requests.post(
    "https://apibox.io.vn/v1/vn-diacritics",
    headers={"Authorization": "Bearer YOUR_API_KEY"},
    json={"text": "Ngan hang Nha nuoc vua giam lai suat dieu hanh", "alternatives": 2},
    timeout=30,
)
print(res.json())

<?php
$ch = curl_init('https://apibox.io.vn/v1/vn-diacritics');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_CUSTOMREQUEST => 'POST',
    CURLOPT_HTTPHEADER => ['Authorization: Bearer YOUR_API_KEY', 'Content-Type: application/json'],
    CURLOPT_POSTFIELDS => '{"text":"Ngan hang Nha nuoc vua giam lai suat dieu hanh","alternatives":2}',
]);
$response = curl_exec($ch);
print_r(json_decode($response, true));

API documentation → Get a free API key

FAQ

How accurate is it?

Common phrases come out right most of the time; ambiguous short words may be wrong, which is why alternatives are offered.

Does it use AI?

No, a dictionary of words and syllable frequencies with dynamic programming, so it is fast and deterministic.

Can I send text that already has some accents?

Yes. Syllables that already have accents are kept unchanged and only the unaccented ones are restored, e.g. “Hôm nay troi dep qua” → “Hôm nay trời đẹp quá”.