Cloud-based accessibility scans run on a remote server that loads your web pages and evaluates them against WCAG (Web Content Accessibility Guidelines) criteria. Local scans run directly in your browser or on your machine, evaluating pages from your own environment. Both types flag approximately 25% of accessibility issues, but how they get there differs in meaningful ways.
| Key Point | What It Means |
|---|---|
| Detection Rate | Both cloud and local scans detect approximately 25% of accessibility issues. The remaining 75% requires (manual) evaluation by a trained professional. |
| Where They Run | Cloud scans operate on a remote server. Local scans run in your browser or local development environment. |
| Authenticated Pages | Local scans, particularly browser extensions, can evaluate pages behind a login. Cloud scans often require additional configuration for authenticated content. |
| Scale | Cloud scans are designed to evaluate large volumes of pages automatically. Local scans are better suited for targeted, page-by-page review. |
How Cloud-Based Accessibility Scans Work
A cloud-based scan takes a URL, loads the page on a remote server, and runs automated checks against WCAG criteria. It evaluates the rendered HTML, CSS, and ARIA attributes without requiring any software on your machine.
Cloud scans are well suited for recurring monitoring. Many organizations schedule them daily, weekly, or monthly to track whether new content introduces new issues. Because the scan runs remotely, it can process hundreds or thousands of pages in a single pass.
The limitation with cloud scans is authenticated content. Pages that require a login session are not accessible to a remote server by default. Some services support authentication tokens or credentials, but the setup is more involved than scanning public pages.
How Local Accessibility Scans Work
Local scans run within your browser, typically through a browser extension or a command-line tool on your machine. The scan evaluates the page as it appears in your active session.
This makes local scans particularly useful for authenticated pages. If you are logged into an application, the extension can evaluate the page you are viewing, including content behind login screens, dashboards, and user-specific views. There is no need to pass credentials to an external server.
Local scans are also practical during development. A developer can run a scan on a staging page before it goes live and catch flagged issues early. The tradeoff is scale. Running a local scan on hundreds of pages requires repeating the process page by page.
Cloud vs Local Accessibility Scans for Monitoring
Monitoring is the practice of running scans on a recurring schedule to track accessibility over time. Cloud-based scans are the standard approach for monitoring because they run automatically without manual interaction.
Local scans are not designed for monitoring. They require someone to open each page and initiate the scan. For ongoing oversight of a live site, cloud-based scans are the more practical fit.
Which Scan Type Fits Where
The choice between cloud and local scans is not either/or. Many organizations use both. Cloud scans cover the public-facing site at scale and provide ongoing monitoring data. Local scans complement them by evaluating authenticated pages and content in development environments.
Neither type replaces a (manual) audit. Both cloud and local scans evaluate the same subset of WCAG criteria through automated checks. The 75% of issues that require human judgment, including screen reader testing, keyboard testing, and contextual evaluation, remain outside the scope of any automated scan.
Choosing a scan type depends on what you need to evaluate and how often. For most organizations, the answer includes both.