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unsane
A tiny, zero-dependency, run-anywhere HTML sanitization library written in TypeScript.
Unsane
A tiny, zero-dependency, run-anywhere HTML sanitization library written in TypeScript.
Features
- Lightweight: ~3.2KB minified, ~1.4KB minified+gzipped
- Zero dependencies: Includes internal HTML entity encoder/decoder and state machine tokenizer
- Run anywhere: Doesn't rely on DOM APIs, JSDOM, or Node APIs, so you can use in any environment
Installation
npm install unsane
Requirements
Unsane requires Node.js 14 or later.
Usage
Basic Usage
// ES Modules
import { sanitize } from "unsane";
// CommonJS
const { sanitize } = require("unsane");
// Input: potentially malicious HTML
const dirty =
'<script>alert("xss")</script><div onclick="alert(`pwned`)">Hello</div>';
// Output: clean HTML with dangerous elements/attributes removed
const clean = sanitize(dirty);
// -> '<div>Hello</div>'
Configuration Options
You can customize the sanitizer behavior with options:
import { sanitize } from "unsane";
const options = {
// Custom list of allowed tags
allowedTags: ["p", "span", "strong", "em", "a", "img"],
// Custom list of allowed attributes for each tag
allowedAttributes: {
a: ["href", "target"],
img: ["src", "alt", "width", "height"],
"*": ["id", "class"], // Attributes allowed on all elements
},
// Allowed URL schemes for href/src attributes
allowedProtocols: ["http:", "https:", "mailto:"]
};
const dirty =
'<script>alert("xss")</script><a href="https://example.com" onclick="hack()" style="color:red">Link</a>';
const clean = sanitize(dirty, options);
// -> '<a href="https://example.com">Link</a>'
Available options:
allowedTags– array of tag names that are kept in the sanitized output.allowedAttributes– object mapping tag names to allowed attributes. Use"*"for attributes allowed on all tags.allowedProtocols– array of URL protocols allowed in attributes likehreforsrc.
HTML Entity Functions
import { encode, decode, escape } from "unsane";
// Encode special characters into entities
const encoded = encode('<div>"text"</div>');
// -> '<div>"text"</div>'
// Decode HTML entities
const decoded = decode("<div>"text"</div>");
// -> '<div>"text"</div>'
// Escape HTML special characters
const escaped = escape('<script>"alert"</script>');
// -> '<script>"alert"</script>'
CLI Usage
You can also sanitize input directly from the command line:
echo '<script>alert("xss")</script>' | npx unsane
This reads HTML from stdin and prints the sanitized result to stdout.
Bundle Size
This library is designed to be lightweight while providing comprehensive HTML sanitization:
| Metric | Size |
|---|---|
| Unpacked | ~15.69 KB |
| Minified | ~3.1 KB |
| Minified + Gzipped | ~1.31 KB |
You can check the package size yourself with:
npm run analyze-size
Threat Model
- Supported contexts: Designed for server-side rendering pipelines and JavaScript runtimes (Node.js ≥14, Cloudflare Workers, Deno) where DOM APIs are unavailable. Browser usage is possible, but the sanitizer never mutates DOM nodes directly; it only returns sanitized HTML strings.
- Supported inputs: Operates on HTML fragments (snippets destined for innerHTML/text interpolation). Full documents (
<!DOCTYPE>,<html>,<head>) are normalized but not guaranteed to preserve structure. - Guarantees: Removes elements outside a conservative allowlist, strips disallowed attributes (especially event handlers and URL-bearing attributes with non-HTTP(S)/mailto/tel/ftp/sms protocols), encodes suspicious inline text, and self-closes void tags.
- Non-goals / exclusions: Does not sanitize or interpret CSS (
styleattributes are dropped), JavaScript, MathML, or SVG namespaces—content in those namespaces is removed rather than partially sanitized. It does not attempt to sanitize inline<style>blocks or external resources (<link>,<script>,<iframe>, etc.) and should be paired with CSPs. - Consumer responsibilities: Validate that customized
allowedTags/allowedAttributesmeet your application’s needs, run application-specific allowlist tests, and apply additional sanitization for CSS/URL rewriting if end users can supply styles or alternate protocols. - Intended use: Defense-in-depth for semi-trusted markup (e.g., Markdown already filtered elsewhere). Do not treat Unsane as a drop-in replacement for battle-tested libraries like DOMPurify without additional auditing, fuzzing, and monitoring.
Security Features
Unsane is designed to protect against common XSS vectors:
- Removes dangerous tags like
<script>,<style>,<iframe>, etc. - Strips event handler attributes (
onclick,onerror, etc.) - Removes
javascript:URLs and other dangerous protocols - Handles unicode escape sequences in URLs
- Properly encodes HTML entities
- Maintains HTML structure to prevent invalid nesting exploits
- Properly handles HTML edge cases with state machine-based parsing
- Robust handling of attribute values with proper quote parsing
Browser Compatibility
Works in all modern browsers as well as Node.js environments. No DOM or browser APIs are required.
Contributing
Please see CONTRIBUTING.md for instructions on setting up the project and running tests. The dist directory is generated and should not be committed.
License
MIT
FAQs
A tiny, zero-dependency, run-anywhere HTML sanitization library written in TypeScript.
We found that unsane demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
Package last updated on 23 Oct 2025
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