Paste one colour code and get HEX, RGB and HSL, plus whether it is readable as text.
WCAG 2 sets 4.5:1 as the AA criterion for body text and 7:1 for AAA; large text (18pt, or bold 14pt) passes AA at 3:1. (WCAG is the W3C's web accessibility guideline.) Blue #2457E6 is about 5.9:1 on white, fine for body text, but 3.6:1 on black, which only suits large text.
HSL separates hue, saturation and lightness, so making a colour lighter or darker means changing only L. The lightness scale below is exactly that; click a step to load it.
#RGB, #RRGGBB, #RRGGBBAA, rgb()/rgba(), hsl()/hsla(), a bare triple like '36, 87, 230', and about fifty common CSS colour names.
No. Conversion and contrast maths run in your browser.
#RRGGBBAA and rgba() are reflected in the HEX and RGB output. Contrast ignores alpha and treats the colour as opaque.
Print CMYK depends on the colour profile, so it is out of scope here.