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HTML_CodeSniffer

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What HTML_CodeSniffer is

HTML_CodeSniffer is a free, open-source checker for HTML coding standards. Written entirely in JavaScript, it performs client-side checks without requiring server-side processing. Included accessibility standards cover WCAG 2.1 Levels A, AA, and AAA, plus Section 508. The auditor reports messages from the selected standard and, where possible, identifies the HTML element linked to an issue. You can call it from JavaScript, use its bookmarklet auditor, or run it from the command line with a headless browser. The project documents npm installation as a Node.js module and server-side checking of HTML fragments with Node.js and a DOM environment such as JSDom. Developers can create custom sniffs and standards. The bookmarklet is designed for Chrome, Firefox, Safari, and Internet Explorer. English is included by default, with French and Polish translations and support for custom translations. The BSD 3-Clause project can be self-hosted by placing its built auditor in a web-accessible location.

Who it suits

HTML_CodeSniffer suits developers and accessibility reviewers checking pages or fragments against WCAG, Section 508, or custom standards. Its JavaScript, bookmarklet, command-line, and Node.js options support different workflows.

What it does well

  • Free and open source
  • WCAG 2.1 and Section 508 checks
  • Custom sniffs and standards
  • JavaScript and command-line use
  • Bookmarklet supports four browsers

What to know first

  • Browser extension is not available
  • Auditor translations are basic
  • Requires setup for self-hosting

Verdict

HTML_CodeSniffer provides several ways to inspect HTML against accessibility and coding rules, including custom standards. Its client-side design and documented Node.js routes make it adaptable for page or fragment checks.

Facts from HTML_CodeSniffer's own pages

Accessibility standards
It includes checks for WCAG 2.1 Levels A, AA, and AAA, and Section 508. · squizlabs.github.io, 12 Oct 2026
API access
Yes · squizlabs.github.io, 21 Sept 2026
Auditor feedback
The auditor displays messages emitted by a standard and, where possible, points to the HTML element causing an issue. · github.com, 12 Oct 2026
Bookmarklet
Its auditor bookmarklet can run accessibility checks on web pages and is stated to work with Chrome, Firefox, Safari and Internet Explorer. · squizlabs.github.io, 12 Oct 2026
Bookmarklet auditor
A bookmarklet provides an auditor interface for checking pages and browsing detected issues; where possible, it points to the HTML element causing the problem. · github.com, 12 Oct 2026
Browser extension
No · squizlabs.github.io, 21 Sept 2026
Browser support
The site says its auditor bookmarklet is designed to work with Google Chrome, Firefox, Safari, and Internet Explorer. · squizlabs.github.io, 12 Oct 2026
Client-side operation
The script is written entirely in JavaScript and does not require server-side processing. · squizlabs.github.io, 12 Oct 2026
Custom rules
Developers can create custom sniffs and write their own standards. · github.com, 12 Oct 2026
Custom standards
Developers can extend it with custom coding standards by creating their own sniffs. · squizlabs.github.io, 12 Oct 2026
Included standards
The site lists WCAG 2.1 Levels A, AA and AAA, and Section 508 among its included standards. · squizlabs.github.io, 12 Oct 2026
Languages
The README says the auditor has English by default, plus French and Polish translations, and can be extended with custom translations. · github.com, 12 Oct 2026
License
The GitHub repository identifies the project license as BSD 3-Clause. · github.com, 12 Oct 2026
Node.js
The README documents installing HTML_CodeSniffer as a Node.js module with npm. · github.com, 12 Oct 2026
Purpose
HTML_CodeSniffer checks HTML source code for violations of a defined coding standard. · squizlabs.github.io, 12 Oct 2026
Scan scope
page · squizlabs.github.io, 21 Sept 2026
Self-hosting
The README describes building the auditor and moving its build directory to a web-accessible location. · github.com, 12 Oct 2026
Server-side use
The README says it can run server-side on HTML fragments using Node.js and a DOM environment such as JSDom. · github.com, 12 Oct 2026
Support
The project README directs users to its GitHub issue tracker to report problems and welcomes contributions through pull requests. · github.com, 12 Oct 2026
Technology
It is a client-side script written entirely in JavaScript and requires no server-side processing. · squizlabs.github.io, 12 Oct 2026
Translations
The auditor supports English by default, French, and Polish; the README describes translations as very basic string translations. · github.com, 12 Oct 2026
Ways to run
The project README describes calling it from JavaScript, using its bookmarklet auditor, or running it on the command line with a headless browser. · github.com, 12 Oct 2026
WCAG version
wcag 2.1 · squizlabs.github.io, 21 Sept 2026

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