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To check color contrast, measure the luminance ratio between the text or meaningful visual element and the color immediately behind or beside it. Under WCAG 2.2 AA, ordinary text generally needs at least 4.5:1 contrast; qualifying large-scale text needs 3:1. Some interface boundaries and graphic information have a separate 3:1 requirement. A contrast checker can calculate a selected pair, but you still need to identify the right colors and states.
What contrast accessibility requires
WCAG measures contrast by relative luminance, not by whether two colors have different names or hues. The central text requirement is WCAG 2.2 Success Criterion 1.4.3, Contrast (Minimum), a Level AA criterion. Its wording requires a contrast ratio of at least 4.5:1 for text and images of text, subject to listed exceptions. Large-scale text generally needs at least 3:1. See the W3C explanation of SC 1.4.3.
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| What you are checking | General WCAG threshold | Criterion |
|---|---|---|
| Ordinary text and images of text | At least 4.5:1 | WCAG 2.2 SC 1.4.3, Level AA |
| Large-scale text and images of large-scale text | At least 3:1 | WCAG 2.2 SC 1.4.3, Level AA |
| Qualifying visual information needed to identify interface components or graphical objects | Generally at least 3:1 against adjacent color(s), with exceptions | WCAG 2.1 SC 1.4.11, Non-text Contrast |
| Ordinary text at the enhanced AAA level | At least 7:1 | WCAG 2.1 SC 1.4.6, Level AAA |
| Large-scale text at the enhanced AAA level | At least 4.5:1 | WCAG 2.1 SC 1.4.6, Level AAA |
“Large-scale” is a defined text-size category, commonly summarized as at least 18 pt regular or 14 pt bold. Do not treat heading status, prominence, or visual importance alone as qualifying text. Assess rendered size according to the criterion and the applicable guidance in W3C Technique G18.
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SC 1.4.3 exceptions include inactive interface components, pure decoration, content not visible to anyone, text in a picture containing significant other visual content, and logotypes. SC 1.4.11 also has criterion-specific exceptions. The non-text rule is not a requirement that every decorative image or every page pixel reach 3:1; it concerns visual information needed to identify relevant components and graphics. Read the W3C explanation of SC 1.4.11 for scope.
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How to check a color pair
- Choose the item and its real neighbor. Identify whether you are assessing text, an icon, a control boundary, or another meaningful graphic. For text, compare its foreground with the background immediately behind it in normal presentation. For non-text information, check against the adjacent color or colors relevant to identifying it.
- Get the colors used in the actual design. Use design tokens, CSS or computed styles, or an on-screen sampling tool. A checker that accepts HEX values is useful only if those values represent the actual pair. If a foreground or background color is unspecified, the pair may not be evaluable without knowing what is rendered behind it.
- Calculate or inspect the ratio. The formula is
(L1 + 0.05) / (L2 + 0.05), where L1 is the lighter color’s relative luminance and L2 the darker color’s. For sRGB, the channels are linearized before relative luminance is calculated; W3C Technique G18 describes the method. - Apply the threshold that matches the item. Use 4.5:1 for ordinary text, 3:1 for qualifying large-scale text, and generally 3:1 for qualifying non-text information. The AAA figures are enhanced targets, not the general AA minimum.
- Record the result without rounding up. A result below the threshold does not pass because it is close. W3C explicitly notes that 4.499:1 does not meet 4.5:1.
For a design-stage option, Figma’s Color Contrast Checker documents foreground and background HEX input, AA/AAA feedback, a swap control, color simulation options, and palette adjustment into Figma Design. It is an example of a tool for people working in Figma, not a W3C endorsement.
Check the whole interface, not just a sample pair
A checker measures the colors it receives or detects. It cannot decide by itself which pairs matter across a page or whether you selected the right state. Review text, icons, meaningful graphical objects, and control boundaries, including relevant normal presentation states. Gradients, images, and overlays may change the background behind text; a single sample from a complex area may not represent the whole item. Check the actual rendered design rather than assuming one foreground/background pair covers every state.
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WAI’s Easy Checks first-review guide puts contrast checking in the context of a broader accessibility review. The W3C Web Accessibility Evaluation Tools List catalogs tools, but W3C says it does not endorse specific products.
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How to improve a failing combination
- Change one or both colors. Darken the darker color, lighten the lighter color, or choose a different pair so their luminance difference increases.
- Keep the design intent where possible. If brand colors must remain, consider using a darker text token, a lighter surface, or a solid backing behind text placed over an image or gradient.
- Recheck the exact element and state. Verify the changed text, icon, boundary, or graphic against the actual adjacent color. Re-test other states or backgrounds that use the same component.
- Check that the change did not hide another issue. Improving text contrast does not automatically establish that a control boundary or icon passes its separate non-text requirement.
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If your task is to capture a website page for review, ScreenshotNeo is a website screenshot API and MCP server. Its one-call API can return an image or PDF; screenshots are useful for viewing a rendered page, but a screenshot alone does not calculate a WCAG contrast ratio. The API accepts a URL in a GET request:
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ScreenshotNeo API documentation
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpScreenshotNeo accepts cookie or consent banners before capture and removes more than 60 known consent platforms, newsletter popups, and chat widgets; each step can be turned off. Bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits cost nothing, and response headers report the page verdict and billing status. Its MCP server provides take_screenshot, get_page_info, and capture_pdf for Claude, Cursor, and other MCP clients. The free plan includes 1,000 screenshots a month with no card; paid plans start at $5 for 3,000 shots. Sign up for ScreenshotNeo’s free plan.
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