Zero CLS Fallback APCA Scoring Variable Fonts
Professional font comparison tool: test any two Google Fonts or system fonts side by side with your own text. Check APCA contrast, WCAG compliance, and Core Web Vitals optimization — all in one free workspace.
Zero CLS — Copy these @font-face rules to eliminate layout shift
Choose from System Fonts (installed on your machine) or Google Fonts (1,600+ web fonts). Use the category filter to narrow by Serif, Sans, Display, Handwriting, Monospace, or Variable.
Type your own text — a headline, brand name, or paragraph — to see how each font handles real content. Both panels update instantly, so you can compare apples to apples.
Both fonts inherit size, weight, letter-spacing, and line-height from the same toolbar. This ensures your comparison is fair. Variable fonts expose additional axes like Width, Optical Size, and Grade.
Each font card shows an APCA badge — Gold (Lc 75+) for small text, Silver (Lc 60+) for body copy, Bronze (Lc 45+) for large text. Click Fix to auto-adjust colors for compliance.
Toggle APCA vs WCAG to see both compliance standards. WCAG 2.1 requires 4.5:1 for body text and 3:1 for large text — APCA is stricter and more perceptually accurate, especially for dark mode.
Enable CLS Ghosting to see how the fallback font positions relative to the web font. A low shift percentage means your Core Web Vitals score stays green when fonts load.
size-adjust that eliminate layout shift entirely.Click Production Bundle to copy complete CSS with @font-face declarations, metric overrides, and fallbacks. Perfect for dropping into your production stylesheet.
Use the Swap button to exchange fonts between left and right panels. The status bar shows a pairing score — higher scores indicate better x-height alignment, contrast, and category diversity.
Choosing between two typefaces is one of the most consequential decisions in design. A headline font that looks striking at 72px might collapse at 32px. A body font that reads beautifully in print could fail on a low-DPI screen. Side-by-side comparison removes guesswork — it lets you evaluate both fonts under identical conditions, with the same text, at the same size.
Our Font Comparison Lab renders any two Google Fonts or system fonts simultaneously, applying the same weight, spacing, and color to both. You can quickly answer questions like: Which serif has a better x-height? Which sans-serif reads more clearly at 16px? Does the display font pair well with the body font?
Web typography requires more than aesthetic judgment. Fonts must load quickly, render consistently across browsers, and pass accessibility standards. Our comparison tool surfaces all three concerns in one view: APCA contrast scoring (the modern replacement for WCAG 2.1), variable font axes, and Core Web Vitals optimization through zero-CLS fallback generation.
For developers, the tool exports production-ready CSS with @font-face declarations, metric overrides, and size-adjust values. Copy the bundle directly into your stylesheet to eliminate layout shift when web fonts load — a common cause of poor CLS scores.
Brand teams use the tool to audition typefaces before committing to licenses. Editorial designers compare headline and body fonts to find combinations that hold up across print, web, and mobile. The pairing score in the status bar suggests optimal combinations based on x-height alignment and category contrast.
All 1,600+ Google Fonts and your locally installed system fonts are available instantly. No account, no download, no limits. Compare as many font pairs as you need. Save your work automatically, or export the CSS bundle for use in your own project.
Open the Font Comparison Lab, select two fonts from the left and right dropdowns, and type your sample text. Both fonts render at the same size, weight, and spacing. Use the Swap button to test each font in both positions.
APCA (Accessible Perceptual Contrast Algorithm) is the modern replacement for WCAG 2.1 contrast ratios, designed for the WCAG 3.0 standard. It measures perceptual contrast more accurately than the older ratio method, especially for dark mode and thin font weights.
Use the built-in APCA and WCAG indicators. Aim for APCA Silver (Lc 60+) for body text and APCA Gold (Lc 75+) for small text. WCAG 2.1 AA requires 4.5:1 for normal text and 3:1 for large text. The Fix button auto-adjusts colors to meet these standards.
Zero-CLS fallback uses @font-face with size-adjust, ascent-override, descent-override, and line-gap-override to make the fallback font render at the same metrics as the web font. This eliminates layout shift when the web font loads, improving Core Web Vitals. Click "Generate Zero-CLS Fallback" to get the CSS.
Yes. Set the left panel to "System" and the right panel to "Google" — or vice versa. Our tool supports both font sources simultaneously, allowing you to test whether a free Google Font can replace a system font you currently use.
The pairing score in the status bar evaluates how well two selected fonts work together. It's calculated from x-height similarity, contrast level (dissimilar categories pair better), and known complementary font pairings. A score of 85%+ indicates a strong pairing.
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