If a solicitation says your website, app, or document must be “508 compliant” or “accessible,” what it almost always means in practice is WCAG 2.1 Level AA. WCAG — the Web Content Accessibility Guidelines, published by the World Wide Web Consortium (W3C) — is the technical rulebook for building digital content people with disabilities can actually use. This is a plain-English walkthrough of what WCAG 2.1 AA requires, how its conformance levels work, and why AA (not A, not AAA) is the line nearly every federal and state contract draws. We bid federal and state IT work every week, and accessibility language shows up constantly — so this is the explainer we wish more vendors read first. This is educational, not legal advice: verify the exact standard against your specific solicitation and the Section 508 requirements that apply.
WCAG, POUR, and why “AA” is the number that matters
Start with the structure — it makes every requirement easier to read.
WCAG is maintained by the W3C, the international standards body for the web. WCAG 2.1 — published as a W3C Recommendation in 2018 — organizes every requirement under four foundational principles, known by the acronym POUR.
Perceivable
Users must be able to perceive the information — through sight, sound, or touch. This covers text alternatives for images, captions for video, and sufficient color contrast so text is legible.
Operable
The interface must be operable by everyone, not just mouse users. Everything must work by keyboard, focus must be visible, and users need enough time and control to complete tasks.
Understandable
Content and operation must be understandable — readable text, predictable behavior, clear labels and instructions, and helpful error messages when something goes wrong.
Robust
Content must be robust enough to work reliably with assistive technologies like screen readers — which means valid, well-structured code that tools can parse correctly.
Why AA, specifically? WCAG defines three conformance levels. Level A is the bare minimum — meeting it alone still leaves major barriers. Level AAA is the highest bar, but the W3C itself notes it is not recommended as a blanket requirement for entire sites because some content cannot meet every AAA criterion. Level AA sits in the practical middle, and that is exactly why laws, policies, and procurement language converge on it.
A vs. AA vs. AAA — what conformance actually means
The levels stack: AA includes all of A, and AAA includes all of A and AA.
| Level | What it is | Where you see it |
|---|---|---|
| A | Minimum conformance. Removes the most fundamental barriers, but not enough on its own. | Rarely the contract target — usually a floor, not a goal. |
| AA | Includes all Level A criteria plus the AA set. The widely accepted compliance standard. | Section 508, most state laws, and the typical solicitation requirement. |
| AAA | Highest level. Includes A and AA plus stricter criteria. Not advised as a site-wide mandate. | Targeted enhancements; specialized contexts. |
To claim AA conformance, a page must satisfy every applicable Level A and Level AA success criterion — you do not get to pick and choose. There is no partial “mostly AA.” WCAG 2.1 added 17 new success criteria on top of WCAG 2.0, broadening coverage for mobile devices, low-vision users, and cognitive and learning disabilities. Of those 17, seven are at Level AA — including Reflow, Non-Text Contrast, Text Spacing, and Status Messages.
Counts evolve across WCAG versions (2.0, 2.1, 2.2). If a contract requires an exact criteria count or a specific version, confirm it against the official spec at w3.org/TR/WCAG21 rather than a third-party summary.
Important AA success criteria, in plain terms
A representative sample — not the full list — of what AA conformance demands.
Color contrast (1.4.3)
Normal text needs a contrast ratio of at least 4.5:1 against its background; large text needs 3:1. Low-contrast gray-on-white fails this constantly.
Keyboard accessible (2.1.1)
Every function must work using only a keyboard — no mouse-only menus, drag-and-drop traps, or hover-only controls that lock out non-mouse users.
Focus visible (2.4.7)
When a user tabs through a page, the element in focus must show a visible indicator. Removing the focus outline in CSS is a common, avoidable failure.
Resize text (1.4.4)
Text must scale up to 200% without loss of content or function — no clipped, overlapping, or disappearing text when a user zooms in.
Labels & instructions (3.3.2)
Form inputs need clear, programmatically associated labels so screen-reader users know what each field expects.
Reflow & spacing (2.1 adds)
New in 2.1: content must reflow to a narrow viewport without horizontal scrolling, and remain readable when users adjust text spacing.
An automated scanner is a floor, not a certification. Tools reliably catch contrast and missing-label issues, but they cannot judge whether alt text is meaningful, whether focus order is logical, or whether a custom widget is truly operable. Real AA conformance pairs automated checks with manual and assistive-technology testing. Run a quick first pass with our accessibility checker, then plan for human review.
How WCAG 2.1 AA relates to Section 508
Two different things that get used as if they were the same.
Section 508 of the Rehabilitation Act is U.S. law requiring federal agencies’ information and communication technology to be accessible. WCAG is the technical standard that defines what “accessible” means in measurable terms. The two connect by reference: the U.S. Access Board’s Revised 508 Standards (effective January 2018) incorporate the W3C’s WCAG Level A and Level AA success criteria by reference for web content. In short — 508 is the legal obligation; WCAG AA is the yardstick it points to.
For federal contracts
If you build or deliver digital ICT to a federal agency, expect AA conformance and an Accessibility Conformance Report (often a VPAT) in the deliverables. Read the exact WCAG version the solicitation cites.
For state & commercial work
Many states and private accessibility expectations also default to WCAG 2.1 AA. The principle is the same: AA is the practical compliance line nationwide and overseas alike.
This is educational, not legal advice. The Access Board updates standards over time and individual solicitations vary — verify the governing version and scope against the U.S. Access Board ICT standards, Section508.gov, and your specific contract. Need a deeper read on the law? See our Section 508 compliance guide.