A scan is an automated check that runs against a web page and flags accessibility issues it can detect through code inspection. An audit is a (manual) evaluation conducted by an accessibility professional who works through the full WCAG standard using screen reader testing, keyboard testing, visual inspection, and code inspection. Scans detect approximately 25% of accessibility issues. Audits cover the remaining 75% that require human judgment, plus the issues a scan can catch.
| Key Point | What It Means |
|---|---|
| Method | Scans are automated. Audits are conducted by humans. |
| Coverage | Scans detect approximately 25% of issues. Audits cover the full WCAG standard. |
| Speed | Scans return results in seconds. Audits take days to weeks depending on scope. |
| Cost | Scans range from free to subscription pricing. Most audits start at $1,000 and range to $3,000. |
| Output | Scans produce a list of flagged code issues. Audits produce a report with prioritized issues, locations, and remediation guidance. |
How a Scan Works
A scan loads a web page and runs automated checks against WCAG success criteria. It evaluates HTML, CSS, and ARIA attributes to detect issues that can be identified through code patterns alone.
Scans excel at finding programmatic issues. Missing alt attributes, empty form labels, improper heading structure, and certain ARIA misuses are detectable by an automated check. The scanner reads the rendered code and compares it against rules.
What a scan cannot do is evaluate context. It cannot determine whether an alt attribute is meaningful, whether a heading describes its section, or whether a custom interactive component behaves correctly with a screen reader. These judgments require a person.
How an Audit Works
An audit is a thorough evaluation of a digital product against the full WCAG standard at a specified conformance level (typically 2.1 AA or 2.2 AA). An accessibility professional works through each page or screen using a defined methodology.
The methodology includes screen reader testing with NVDA, JAWS, or VoiceOver, keyboard testing across all interactive elements, visual inspection at 200% and 400% browser zoom, code inspection, and an automated scan as one component of the review. The auditor identifies every issue that affects conformance, not only those a scan would flag.
The output is an audit report listing each issue with its location, the WCAG criterion it relates to, severity, and remediation guidance. This is what development teams use to fix issues and what organizations reference when documenting conformance.
What Scans Miss
The 75% of WCAG issues that scans cannot detect involve human-facing experience. A form may have a label in the code but the label may not describe the field correctly. A modal may open but the focus may not move to it. A video may have captions but the captions may not match the audio.
These issues require someone to interact with the product the way a user would. A scan reads code. An audit evaluates experience.
When Each Is Appropriate
Scans are useful for ongoing monitoring, regression detection, and catching obvious code issues during development. Running scheduled scans (daily, weekly, or monthly) helps teams catch new issues as they appear.
Audits are appropriate when an organization needs to document conformance, prepare a VPAT or ACR, respond to a procurement request, or establish a baseline before remediation. They are also the correct evaluation when reducing legal risk under ADA Title II or Title III.
Most accessibility programs use both. Scans provide continuous coverage of detectable issues. Audits provide depth and full WCAG coverage at defined intervals.
Why the Distinction Matters
Treating a scan as a substitute for an audit produces a false sense of conformance. A page can pass a scan and still have severe accessibility issues that prevent users from completing core tasks. Conformance claims, VPAT documentation, and risk reduction strategies require evaluation that goes beyond what automation can detect.
A scan tells you what a machine can find. An audit tells you what a user will experience.