# html-encoding-sniffer

> Sniff the encoding from a HTML byte stream

Latest version **6.0.0** (published 2025-12-26) · MIT license · 0 weekly downloads

## Install

```sh
npm install html-encoding-sniffer
pnpm add html-encoding-sniffer
yarn add html-encoding-sniffer
bun add html-encoding-sniffer
```

## Health

**Score 58/100 (C)** — status: stable.

Positive: has types package; no vulnerabilities; has provenance; high quality score.

Warnings: low downloads; no esm support.

## Facts

| | |
|---|---|
| Version | 6.0.0 |
| Published | 2025-12-26 |
| First published | 2016-10-16 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | separate (@types/html-encoding-sniffer) |
| Module format | CommonJS |
| Node | ^20.19.0 \|\| ^22.12.0 \|\| >=24.0.0 |
| Dependencies | 1 |
| Unpacked size | 11.9 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| Provenance | attested (GitHub Actions) |
| GitHub stars | 21 |
| Author | Domenic Denicola |
| Maintainers | timothygu, domenic, sebmaster, zirro, tmpvar, joris-van-der-wel |
| Keywords | encoding, html |

## Links

- npm: https://www.npmjs.com/package/html-encoding-sniffer
- Repository: https://github.com/jsdom/html-encoding-sniffer
- Homepage: https://github.com/jsdom/html-encoding-sniffer#readme
- Issues: https://github.com/jsdom/html-encoding-sniffer/issues
- npm.io page: https://npm.io/package/html-encoding-sniffer

## Dependencies (1)

- [@exodus/bytes](https://npm.io/package/@exodus/bytes.md) ^1.6.0

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## Recent versions

- 6.0.0 (latest) — 2025-12-26
- 5.0.0 — 2025-12-23
- 4.0.0 — 2023-11-12
- 3.0.0 — 2021-09-18
- 2.0.1 — 2020-02-23
- 2.0.0 — 2020-01-05
- 1.0.2 — 2017-10-23
- 1.0.1 — 2016-10-16
- 1.0.0 — 2016-10-16

## README

# Determine the Encoding of a HTML Byte Stream

This package implements the HTML Standard's [encoding sniffing algorithm](https://html.spec.whatwg.org/multipage/syntax.html#encoding-sniffing-algorithm) in all its glory. The most interesting part of this is how it pre-scans the first 1024 bytes in order to search for certain `<meta charset>`-related patterns.

```js
const htmlEncodingSniffer = require("html-encoding-sniffer");
const fs = require("fs");

const htmlBytes = fs.readFileSync("./html-page.html");
const sniffedEncoding = htmlEncodingSniffer(htmlBytes);
```

The passed bytes are given as a `Uint8Array`; the Node.js `Buffer` subclass of `Uint8Array` will also work, as shown above.

The returned value will be a canonical [encoding name](https://encoding.spec.whatwg.org/#names-and-labels) (not a label). You might then combine this with the [`@exodus/bytes`](https://github.com/ExodusOSS/bytes/) package to decode the result:

```js
const { TextDecoder } = require("@exodus/bytes");
const htmlString = (new TextDecoder(sniffedEncoding)).decode(htmlBytes);
```

## Options

You can pass the following options to `htmlEncodingSniffer`:

```js
const sniffedEncoding = htmlEncodingSniffer(htmlBytes, {
  xml,
  transportLayerEncodingLabel,
  defaultEncoding,
});
```

The `xml` option is a boolean, defaulting to `false`. If set to `true`, then we bypass the [HTML encoding sniffing algorithm](https://html.spec.whatwg.org/multipage/syntax.html#encoding-sniffing-algorithm) and compute the encoding based on the presence of a BOM, or the other options provided. (In the future, we may perform sniffing of the `<?xml?>` declaration, but for now that is not implemented.)

The `transportLayerEncodingLabel` is an encoding label that is obtained from the "transport layer" (probably a HTTP `Content-Type` header), which overrides everything but a BOM.

The `defaultEncoding` is the ultimate fallback encoding used if no valid encoding is supplied by the transport layer, and no encoding is sniffed from the bytes. For HTML, it defaults to `"windows-1252"`, as recommended by the algorithm's table of suggested defaults for "All other locales" (including the `en` locale). For XML, it defaults to `"UTF-8"`.

## Credits

This package was originally based on the excellent work of [@nicolashenry](https://github.com/nicolashenry), [in jsdom](https://github.com/tmpvar/jsdom/blob/16fd85618f2705d181232f6552125872a37164bc/lib/jsdom/living/helpers/encoding.js). It has since been pulled out into this separate package.

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_Source: https://npm.io/package/html-encoding-sniffer · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._