A scan is an automated check that flags approximately 25% of accessibility issues. An accessibility audit is a thorough, human-led evaluation of a digital asset against a WCAG standard like WCAG 2.1 AA or WCAG 2.2 AA. They are completely separate activities with different purposes, different outputs, and different levels of reliability. A scan can never determine WCAG conformance. A (manual) accessibility audit is the only way to do that.
| Factor | Scan | Accessibility Audit |
|---|---|---|
| Who performs it | Automated software | A trained human auditor |
| Issue coverage | Approximately 25% of issues | All identifiable WCAG issues |
| Can determine WCAG conformance | No | Yes |
| Output | Automated report of flagged issues | Detailed audit report with issue descriptions, locations, and WCAG criteria |
| Speed | Minutes | Days to weeks depending on scope |
| Cost | Free to low monthly fee | Professional service pricing based on pages and complexity |
What Does a Scan Actually Do?
A scan runs automated checks against a web page’s code. It looks for patterns that indicate accessibility issues: missing alt text on images, empty form labels, low color contrast ratios, missing document language attributes. These are real issues, and catching them quickly has value.
But a scan cannot evaluate context. It cannot tell whether alt text is meaningful or whether a keyboard user can move through a complex form. It cannot determine if a screen reader announces content in a logical order. The 75% of WCAG criteria that require human judgment are invisible to automated tools.
Scans are useful as a monitoring layer. They flag surface-level issues between audits and keep known patterns from creeping back into production code. Accessible.org treats scanning as a standalone activity, separate from the audit process.
What Happens During an Accessibility Audit?
An accessibility audit is a structured evaluation conducted by a trained auditor. The auditor goes through each page or screen in scope, evaluating it against every applicable WCAG success criterion at the target conformance level.
The auditor interacts with the content the way real users do. They move through the interface with a keyboard. They use screen readers. They evaluate whether interactive elements communicate their state, whether error messages are associated with their fields, whether dynamic content updates are announced properly. This is where the bulk of accessibility issues are identified, in the interactions that automation cannot replicate.
The output is an audit report. Each issue is documented with its location, the WCAG criterion it maps to, and a description of the problem. That report becomes the foundation for remediation, prioritization, and, if needed, legal documentation of compliance efforts.
Why Can’t a Scan Determine Conformance?
WCAG conformance means every applicable success criterion at a given level is met. A scan only flags approximately 25% of issues. That leaves the majority of criteria unevaluated.
A clean scan result does not mean a page is conformant. It means the automated tool did not detect issues within its narrow scope. Pages with perfect scan scores routinely have dozens of issues that only a human auditor identifies. This is why organizations that rely on scans alone are exposed to both legal risk and a poor user experience for people with disabilities.
A (manual) accessibility audit is the only way to determine WCAG conformance. There is no shortcut, no automated alternative, and no combination of tools that replaces it.
When Does Each One Make Sense?
Scans make sense as a continuous monitoring tool. After an audit and remediation cycle, periodic scans catch regressions: new images missing alt text, color contrast changes from a design update, forms deployed without labels. They are a maintenance layer, not an evaluation method.
An audit makes sense at the beginning of any accessibility effort, after a major redesign, before filling out a VPAT to produce an ACR, or in response to a legal demand. It is the baseline. Without an audit, an organization does not know where it stands against WCAG 2.1 AA or WCAG 2.2 AA.
Accessible.org conducts audits that are always fully human-led. The process behind a thorough accessibility evaluation is built on direct interaction with every page in scope, not automated pattern matching.
Can You Use Both Together?
Yes, but they serve different roles and should not be combined into a single activity. An audit establishes your conformance baseline. Scans monitor for regressions after remediation is complete.
Think of it this way: the audit tells you what needs to be fixed. Remediation addresses those issues. And scans help confirm that the surface-level fixes stay in place over time. Each step has a distinct function in the broader accessibility workflow.
The Accessibility Tracker Platform supports both. Audit data lives in one area. Scan and monitoring data lives in another. They inform each other but are never conflated.
Frequently Asked Questions
Do I need an audit if my scan comes back clean?
Yes. A clean scan means the tool did not detect issues within its scope. Scans only flag approximately 25% of issues. The remaining WCAG criteria require human evaluation. A clean scan is not evidence of conformance.
How often should I run a scan versus getting an audit?
Scans can run weekly or monthly as a monitoring layer. Audits are typically conducted at the start of an accessibility project, after major updates, or annually. Some organizations audit more frequently based on their ADA compliance posture or procurement requirements tied to Section 508 or EN 301 549.
Can a scan replace an audit for VPAT purposes?
No. An ACR requires a full evaluation against WCAG. Since a scan only flags a fraction of issues, it cannot serve as the basis for an ACR. An audit is required to accurately populate the conformance data in a VPAT.
Scans and audits answer different questions. A scan asks, “Are there obvious code-level issues?” An audit asks, “Does this digital asset conform to WCAG?” Both matter. But only one of them gives you a definitive answer about conformance.
Contact Accessible.org to start a conversation about your next accessibility audit.
