Alfa

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Introduction

Alfa is an open, standards-based engine for accessibility conformance testing of websites built with HTML, CSS and JavaScript, against standards such as WCAG. It distils the best parts of Siteimprove’s proprietary engine, which Alfa has replaced, implemented on top of the open Accessibility Conformance Testing (ACT) rules format.

Its rule catalogue uses SIA-R identifiers, for example checks that !important letter, word and line spacing in style attributes is wide enough, that media alternatives exist and that auto-playing audio has a control mechanism. It can be integrated into test frameworks and CI.

Automated checks catch only part of accessibility problems. Combine tools like this with keyboard-only and screen reader testing, and with feedback from disabled users, before claiming conformance.

The source code is at Siteimprove/alfa on GitHub under the MIT licence, with about 135 stars; the most recent commit was on 29 October 2026.

Features

1. ACT rules: Standards-based checks.
2. WCAG coverage: Conformance testing.
3. SIA-R rule catalogue: Documented rules.
4. Framework integrations: Use in tests and CI.
5. Production engine: Powers Siteimprove.

Pros

1. Enterprise-grade engine: Used in a commercial product.
2. Free to use: Open source under the MIT licence, so the core tool costs nothing to use.
3. Actively maintained: The repository had commits as recent as 29 October 2026.

Cons

1. Smaller community: Fewer stars than axe-core.
2. TypeScript focus: JS ecosystem.

Usage and Links (Example)

1. Install the Alfa packages for your test framework (see alfa.siteimprove.com).
2. Audit pages in your E2E tests.
3. Fail CI on new rule violations.

Resources:

• Alfa website
• GitHub repository

Pricing

Alfa is free and open source under the MIT licence.

Recommended for?

1. Teams wanting a standards-based alternative to axe-core.

Conclusion

Alfa is a rigorous ACT-rule engine with commercial pedigree.

Compare its results with axe-core on your pages.

On CheckOps, Alfa is filed under the Accessibility and Release & CI gates stages. Related tools listed here include axe-core, Pa11y, IBM Equal Access Accessibility Checker, Accessibility Insights, Lighthouse and WAVE. When comparing them, weigh the licence, the languages and platforms each supports, whether it is self-hosted or managed, and how cleanly it slots into your existing CI pipeline. Details on this page were checked against the official website, documentation and repository on 11 November 2026.