Site-wide accessibility testing,
powered by
Axe Core
Rocket Validator runs the full Axe Core rule set across your entire website. Enter a URL, and our crawler checks up to 5,000 pages against WCAG 2.0, 2.1, and 2.2 — delivering a single, actionable report in minutes.
What is Axe Core?
The open-source accessibility engine created by Deque Systems — the most widely used automated accessibility testing library in the world.
Released in 2015 under the Mozilla Public License 2.0, Axe Core has become the industry standard for automated accessibility testing. It works as a JavaScript library that analyzes the rendered DOM of a web page — not the raw HTML source, but the actual page as a browser interprets it.
This approach allows Axe Core to accurately evaluate how elements appear and behave for real users, including styles applied via CSS, dynamically injected content, and Shadow DOM components.
Each rule targets specific HTML elements and evaluates them against established accessibility standards. Results are categorized by impact level — critical, serious, moderate, or minor — so teams can prioritize the issues that affect users the most.
The engine is trusted by Google, Microsoft, and thousands of development teams worldwide. It has been integrated into browser extensions, CI/CD pipelines, testing frameworks, and cloud platforms — including Rocket Validator.
Standards covered
Axe Core validates web pages against a comprehensive set of accessibility and compliance standards:
- WCAG 2.0 Level A, AA, and AAA
- WCAG 2.1 Level A and AA
- WCAG 2.2 Level AA (including the target-size rule for Success Criterion 2.5.8)
- Section 508 (US federal accessibility requirements)
- EN 301 549 (the European standard referenced by the European Accessibility Act)
- RGAA v4 (the French accessibility framework, added in Axe Core 4.11.0)
- Trusted Tester v5
Each rule in the Axe Core engine is tagged with the specific standards and success criteria it addresses. When Rocket Validator runs a report, every issue links directly to the relevant WCAG success criterion and includes a detailed remediation guide integrated directly into your report.
How Axe Core works
When Axe Core runs on a page, it follows a systematic process:
1 DOM traversal
The engine builds a virtual "flattened tree" of the rendered page, including content inside Shadow DOM and iframes. This ensures nothing is missed, even in complex component-based architectures.
2 Rule matching
Each of the 80+ rules uses CSS selectors to find the elements it applies to. For example,
the image-alt
rule targets all <img>
elements; the color-contrast
rule targets all visible text nodes.
3 Check evaluation
Once matched, elements are tested through individual checks organized into three groups: checks that must all pass, checks where at least one must pass, and checks that must all fail. This compositional approach allows rules to express complex accessibility logic.
4 Result classification
Every tested element falls into one of four categories: violation (definite failure), pass (confirmed compliance), incomplete (needs human review), or inapplicable (rule did not apply). Each violation includes the element's CSS selector, the specific rule broken, the WCAG criteria affected, and the impact severity.
This structured output is exactly what Rocket Validator consumes when generating your site-wide reports. Every issue you see in a Rocket Validator report comes directly from the Axe Core engine, with no modifications to the rule set or severity classifications.
The zero false positives commitment
Every violation reported by Axe Core, and therefore every violation in your Rocket Validator report, is a real issue that needs attention. There is no noise to filter, no false alarms to triage.
One of Axe Core's defining design principles is its commitment to zero false positives. When the engine cannot definitively determine whether an element violates a rule — for example, when it detects an image has alt text but cannot judge whether that text is meaningful — it classifies the result as "incomplete" (needs review) rather than flagging it as a violation.
Your team can act on every finding with confidence.
Other accessibility testing tools take a different approach, casting a wider net and flagging potential issues that may or may not be actual violations. While this catches more edge cases, it creates significant triage overhead — especially at scale. When you are checking hundreds or thousands of pages, the difference between "every result is actionable" and "some results need manual verification" is the difference between a report your team can use and a report your team ignores.
What automated testing can — and cannot — catch
It is important to be transparent about the scope of automated accessibility testing. Axe Core can automatically detect approximately 57% of the WCAG issues typically found during a first-time accessibility audit. This covers a significant range of common problems:
The remaining 43% of WCAG criteria require human judgment — things like evaluating whether alternative text is actually descriptive, whether focus order is logical, whether audio captions are accurate, or whether error messages are helpful. No automated tool can assess these reliably.
This is not a limitation unique to Axe Core or Rocket Validator — it is a fundamental characteristic of all automated accessibility testing tools. What Rocket Validator does is ensure that you get the most out of the automated portion: running the complete Axe Core rule set across every page on your site, so the issues that can be found automatically are found consistently and at scale.
Axe Core in the browser
vs. Axe Core at scale
Browser extensions check one page at a time.
Rocket Validator automates the entire process.
If you have used the axe DevTools browser extension, you already know how Axe Core works — you open a page, run the extension, and review the results. But to audit a 500-page website, you would need to manually navigate to each page, run the extension, record the results, and somehow aggregate them. That is not practical for anyone managing a site of any significant size.
Automated crawling
Enter a starting URL and our crawler discovers your site's pages automatically. It follows internal links, respects robots.txt, and supports XML sitemaps. Up to 5,000 pages per report.
Full Axe Core on every page
Each discovered page is rendered in a headless browser and tested with the complete Axe Core rule set — all 80+ rules, not just the ~56 used by Google Lighthouse.
Common issue aggregation
Instead of reviewing 500 individual page reports, Rocket Validator groups identical issues across your site — revealing systemic issues versus isolated ones.
Device viewport emulation
Test how your site's accessibility holds up at different screen sizes, including mobile viewports, where responsive layouts often introduce new accessibility problems.
Scheduled reports
Set up daily, weekly, or monthly automated checks to monitor your site's accessibility over time. Get notified when new issues appear or existing ones are resolved.
Deploy hooks
Trigger a new accessibility check automatically after every deployment, catching regressions before they reach your users.
Dual-engine validation: accessibility + HTML
Rocket Validator does not only run Axe Core. Every page is also validated against the W3C Validator Nu for HTML conformance. This dual-engine approach catches issues that neither engine would find alone:
Axe Core
Identifies accessibility violations: missing alt text, insufficient contrast, ARIA misuse.
W3C Validator
Catches HTML errors: unclosed tags, invalid attributes, deprecated elements, structural problems.
Invalid HTML can cause accessibility issues that Axe Core alone might not flag. A malformed
<label>
element, for example, might not associate correctly
with its form field — the HTML validator catches the structural error, while Axe Core catches the
resulting accessibility impact. Together, they provide a more complete picture of your site's quality.
Comparison: testing approaches
Rocket Validator
- Engine
- Axe Core (full) + W3C Validator
- Scope
- Site-wide (up to 5,000 pages)
- WCAG 2.2
- Yes
- EN 301 549
- Yes
- HTML validation
- Yes (W3C Validator Nu)
- Scheduling
- Yes
- Common issue reports
- Yes
- Typical cost
- From $36/month
- Setup
- Enter a URL, click go
Axe DevTools extension
- Engine
- Axe Core (full)
- Scope
- One page at a time
- WCAG 2.2
- Yes
- EN 301 549
- Yes
- HTML validation
- No
- Scheduling
- No
- Common issue reports
- No
- Typical cost
- Free (limited)
- Setup
- Browser install
Google Lighthouse
- Engine
- Axe Core (subset, ~56 rules)
- Scope
- One page at a time
- WCAG 2.2
- Partial
- EN 301 549
- No
- HTML validation
- Partial
- Scheduling
- No
- Common issue reports
- No
- Typical cost
- Free
- Setup
- Built into Chrome
Enterprise platforms
- Engine
- Proprietary
- Scope
- Site-wide
- WCAG 2.2
- Varies
- EN 301 549
- Varies
- HTML validation
- Varies
- Scheduling
- Yes
- Common issue reports
- Yes
- Typical cost
- $15,000–$50,000+/yr
- Setup
- Enterprise onboarding
Detailed guides to help you fix what Axe Core finds
Every accessibility issue detected by Axe Core has a detailed, corresponding guide integrated directly into your report. These guides explain:
- What the rule checks and why it matters
- Which WCAG success criteria it relates to
- Code examples showing the issue and the fix
- Common scenarios where the issue appears
- Links to the relevant WCAG documentation
When you open an issue in your Rocket Validator report, the guide is one click away. No need to search documentation or interpret cryptic error codes.
Talk to your accessibility data
The Rocket Validator MCP Server, currently in public beta, allows AI assistants to query your validation data directly. Ask questions like "which accessibility issues are most common across my sites?" or "show me all pages with color contrast failures" and get answers drawn from your actual reports.
This means Axe Core results are not just stored in a dashboard — they become a structured dataset that AI tools can reason about, compare across reports, and use to track your accessibility progress over time.
European compliance: EAA and EN 301 549
The European Accessibility Act requires companies selling digital products and services to EU customers to meet accessibility standards by June 28, 2025. The technical standard referenced by the EAA is EN 301 549, which incorporates WCAG 2.1 Level AA.
Axe Core includes EN 301 549 as a supported standard, and Rocket Validator runs these checks across your entire site. For European teams — or any team serving European users — this provides a practical, ongoing way to monitor compliance at scale.
Rocket Validator is built and operated from Spain, with servers hosted in European data centers (Paris and Amsterdam). Your validation data stays in Europe.
Get started
Rocket Validator offers a free trial that lets you check up to 25 pages for HTML issues. To test accessibility validation with the full Axe Core engine, Pro trial plans are available at a reduced price.
For ongoing monitoring, Pro plans start at €59/month and include accessibility and HTML validation, scheduling, muting, device viewport emulation, and up to 50,000 checks per month.
Validate at scale.
Ship accessible websites, faster.
Automated HTML & accessibility validation for large sites. Check thousands of pages against WCAG guidelines and W3C standards in minutes, not days.
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