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.

Optimisation	default	advanced	lite
autoprefixer	❌	✅	❌
cssDeclarationSorter	✅	✅	❌
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.

Last updated on Tue, 28 Oct 2025 13:54:40 GMT