Optimisations

What are optimisations?

An optimisation is a module that performs a transform on some CSS code in order to reduce its size, or failing this, the final gzip size of the CSS. Each optimisation is performed by either one module or a few modules working together.

Due to the nature of dividing cssnano's responsibilities across several modules, there will be some cases where using a transform standalone will not produce the most optimal output. For example, postcss-colormin will not trim whitespace inside color functions as this is handled by postcss-normalize-whitespace.

What optimisations do you support?

The optimisations are different depending on which preset cssnano is configured with; with the default preset, we offer safe transforms only.

	default	advanced
autoprefixer	❌	✅
cssDeclarationSorter	✅	✅
rawCache	✅	✅
calc	✅	✅
colormin	✅	✅
convertValues	✅	✅
discardComments	✅	✅
discardDuplicates	✅	✅
discardEmpty	✅	✅
discardOverridden	✅	✅
discardUnused	❌	✅
mergeIdents	❌	✅
mergeLonghand	✅	✅
mergeRules	✅	✅
minifyFontValues	✅	✅
minifyGradients	✅	✅
minifyParams	✅	✅
minifySelectors	✅	✅
normalizeCharset	✅	✅
normalizeDisplayValues	✅	✅
normalizePositions	✅	✅
normalizeRepeatStyle	✅	✅
normalizeString	✅	✅
normalizeTimingFunctions	✅	✅
normalizeUnicode	✅	✅
normalizeUrl	✅	✅
normalizeWhitespace	✅	✅
orderedValues	✅	✅
reduceIdents	❌	✅
reduceInitial	✅	✅
reduceTransforms	✅	✅
svgo	✅	✅
uniqueSelectors	✅	✅
zindex	❌	✅

You can read more about presets in our presets guide.