Color and layout decisions show up in every frontend project — whether you are matching a designer's handoff, checking accessibility, or previewing documentation. These four free tools run in your browser with no signup. See our Complete Developer Tools Guide for the full developer toolkit.
Color Picker
Pick and convert colors between HEX, RGB, and HSL formats — useful when a designer hands over a color in one format but your codebase needs another, or when sampling a color value to reuse consistently across a UI. Save up to ten colors to a palette during a design session. Use Color Picker.
Color Contrast Checker
Check whether a text and background color combination meets WCAG accessibility contrast ratio guidelines — AA and AAA standards. This matters for users with low vision and is increasingly a real compliance requirement for many websites, not just a nice-to-have. See pass/fail badges and a live text preview as you adjust colors. Use Color Contrast Checker.
Aspect Ratio Calculator
Calculate proportional dimensions when resizing an image or video — for example, figuring out what height to use for a fixed width while keeping the original proportions intact, avoiding stretched or squished media. Includes presets for 16:9, 9:16, 1:1, and more. Use Aspect Ratio Calculator.
Markdown to HTML Converter
Convert Markdown-formatted text into rendered HTML — useful for previewing how Markdown content (READMEs, blog drafts, documentation) will look once rendered, or for converting content for a CMS or email that needs HTML rather than raw Markdown syntax. Live preview updates as you type. Use Markdown to HTML Converter.
Frequently Asked Questions
What is a good color contrast ratio for accessibility?
WCAG guidelines recommend a minimum contrast ratio of 4.5:1 for normal text (AA standard) and 7:1 for AAA compliance, with slightly lower thresholds for large text.
How do I calculate aspect ratio for resizing an image?
Aspect ratio is the proportional relationship between width and height (e.g. 16:9). To resize while keeping proportions, calculate the new height (or width) using the same ratio as the original dimensions.
What's the difference between HEX, RGB, and HSL color formats?
HEX is a compact hexadecimal code (e.g. #3B82F6) commonly used in CSS, RGB specifies red/green/blue intensity values directly, and HSL describes color by hue, saturation, and lightness — useful for intuitively adjusting a color's brightness or vibrancy.
Why convert Markdown to HTML instead of just writing HTML directly?
Markdown is faster to write and read in its raw form (especially for documentation and content drafts), but browsers and many platforms need actual HTML to render formatting — converting bridges that gap.
Related Reading
Try Color Picker → · Contrast Checker → · Aspect Ratio → · Markdown to HTML →