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Framework for transforming cascading style sheets (CSS) from left-to-right (LTR) to right-to-left (RTL)


RTLCSS is a framework for converting Left-To-Right (LTR) Cascading Style Sheets(CSS) to Right-To-Left (RTL).

Why RTLCSS Install Basic Usage CLI Advanced Usage Options ☕😆

In a right-to-left, top-to-bottom script (commonly shortened to right to left or abbreviated RTL), writing starts from the right of the page and continues to the left. For example Arabic script (the most widespread RTL writing system in modern times ).

Web development depends heavily on CSS to create visually engaging webpages, user interfaces for web applications, and user interfaces for many mobile applications. CSS defines how HTML elements are to be displayed via Positioning, Box model, Typographic and Visual properties, such as left:10px, padding-left:1em, text-align:right, ... etc.

Browsers will apply these properties AS IS regardless of the document language direction. This means in order for an international website to support RTL languages, it should adjust the entire CSS to render from right to left.

For example, this is how different github would be if it was to be viewed in an RTL language:

Just like a mirror, where everything gets flipped.

Instead of authoring two sets of CSS files, one for each language direction. Now you can author the LTR version and RTLCSS will automatically create the RTL counterpart for you!

.example {
  padding:5px 10px 15px 20px;
  margin:5px 10px 15px 20px;
  border-style:dotted dashed double solid;
  border-width:1px 2px 3px 4px;
  border-color:red green blue black;
  box-shadow: -1em 0 0.4em gray, 3px 3px 30px black;

Will be transformed into:

.example {
  padding:5px 20px 15px 10px;
  margin:5px 20px 15px 10px;
  border-style:dotted solid double dashed;
  border-width:1px 4px 3px 2px;
  border-color:red black blue green;
  box-shadow: 1em 0 0.4em gray, -3px 3px 30px black;
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npm install rtlcss
var rtlcss = require('rtlcss');
var result = rtlcss.process("body { direction:ltr; }");
//result == body { direction:rtl; } 

RTLCSS preserves original input formatting and indentations.

A CSS rule has two main parts: a selector, and one or more declarations:

background border-right-color margin
background-image border-right-style margin-left
background-position border-right-width margin-right
background-position-x border-style padding
border-bottom-left-radius border-top-left-radius padding-left
border-bottom-right-radius border-top-right-radius padding-right
border-color border-width right
border-left box-shadow text-align
border-left-color clear text-shadow
border-left-style cursor transform
border-left-width direction transform-origin
border-radius float transition
border-right left transition-property

When RTLing a CSS document, there are cases where it's impossible to know whether to mirror a property value, whether to change a rule selector, or whether to update a non-directional property. In such cases, RTLCSS provides processing directives in the form of CSS comments. Both standard /*rtl:...*/ and special/important /*!rtl:...*/ notations are supported.

Two sets of directives are available. Control and Value.

Control directives are placed between declarations or statements (rules and at-rules), They can target one node (self-closing) or a set of nodes (block-syntax).

  • Self-closing
.code {
  • Block-syntax
.code {

Available Control Directives:

Name Syntax Description
Ignore /*rtl:ignore*/ Ignores processing of the following node (self-closing) or nodes within scope (block-syntax).
Config /*rtl:config:{OBJECT}*/ Evaluates the {OBJECT} parameter and updates current RTLCSS config*1.
Options /*rtl:options:{JSON}*/ Parses the {JSON} parameter and updates current RTLCSS options*2.
Raw /*rtl:raw:{CSS}*/ Parses the {CSS} parameter and inserts it before the comment node that triggered the directive*3.
Remove /*rtl:remove*/ Removes the following node (self-closing) or nodes within scope (block-syntax).
Rename /*rtl:rename*/ Renames the selector of the following rule (self-closing) or rules within scope (block-syntax) by applying String Maps.
  • 1 Config is evaluated using eval, and it can be disabled by adding it to the blacklist.
  • 2 Options parsing is done via JSON.parse, and requires a valid json. The new options will override the defaults (not the current context). Plugins will be carried over from the current context.
  • 3 Due to the nature of RAW directive, block-syntax is not supported.


  "autoRename": true,
      "name"    : "prev-next",
      "search"  : ["prev", "Prev", "PREV"],
      "replace" : ["next", "Next", "NEXT"],
      "options" : {"ignoreCase":false}
.demo-prev.demo-Prev.demo-PREV { content: 'p'; }
.demo-next.demo-Next.demo-NEXT { content: 'n'; }


.demo-next.demo-Next.demo-NEXT { content: 'p'; }
.demo-prev.demo-Prev.demo-PREV { content: 'n'; }

Value directives are placed any where inside the declaration value. They target the containing declaration node.

Available Value Directives:

Name Syntax Description
Append /*rtl:append:{value}*/ Appends {value} to the end of the declaration value.
Ignore /*rtl:ignore*/ Ignores processing of this declaration.
Insert /*rtl:insert:{value}*/ Inserts {value} to where the directive is located inside the declaration value.
Prepend /*rtl:prepend:{value}*/ Prepends {value} to the begining of the declaration value.
Replace /*rtl:{value}*/ Replaces the declaration value with {value}.


  font-family:"Droid Sans""Helvetica Neue"Arial/*rtl:prepend:"Droid Arabic Kufi", */;


  font-family:"Droid Arabic Kufi""Droid Sans""Helvetica Neue"Arial;

Convert LTR CSS files to RTL using the command line. For usage and available options see CLI documentaion.

$ rtlcss input.css output.rtl.css

// directly processes css and return a string containing the processed css 
output = rtlcss.process(css [, options , plugins]);
output // processed CSS 
// you can also group all configuration settings into a single object 
result = rtlcss.configure(config).process(css, postcssOptions);
result.css // Processed CSS // Source map 

Built on top of PostCSS, an awesome framework, providing you with the power of manipulating CSS via a JS API.

It can be combined with other processors, such as autoprefixer:

var result = postcss().use(rtlcss([options , plugins]))
Option Type Default Description
autoRename boolean false Applies to CSS rules containing no directional properties, it will update the selector by applying String Maps.(See Why Auto-Rename?)
autoRenameStrict boolean false Ensures autoRename is applied only if pair exists.
blacklist object {} An object map of disabled plugins directives, where keys are plugin names and value are object hash of disabled directives. e.g. {'rtlcss':{'config':true}}.
clean boolean true Removes directives comments from output CSS.
greedy boolean false Fallback value for String Maps options.
processUrls boolean or object false Applies String Maps to URLs. You can also target specific node types using an object literal. e.g. {'atrule': true, 'decl': false}.
stringMap array The default array of String Maps.

String map is a collection of map objects, where each defines a mapping between directional strings. It is used in renaming selectors and URL updates.

The following is the default string map:

    'name'    : 'left-right',
    'priority': 100,
    'search'  : ['left', 'Left', 'LEFT'],
    'replace' : ['right', 'Right', 'RIGHT'],
    'options' : {
        'scope' : '*',
        'ignoreCase' : false
    'name'    : 'ltr-rtl',
    'priority': 100,
    'search'  : ['ltr', 'Ltr', 'LTR'],
    'replace' : ['rtl', 'Rtl', 'RTL'],
    'options' : {
        'scope' : '*',
        'ignoreCase' : false

To override any of the default maps, just add your own with the same name. A map object consists of the following:

Property Type Description
name string Name of the map object
priority number Maps are sorted according to prioirity.
exclusive boolean When enabled, prevents applying the remaining maps.
search string or Array The string or list of strings to search for or replace with.
replace string or Array The string or list of strings to search for or replace with.
options object Defines map options.

The map options attribute is optional, and consists of the following:

Property Type Default Description
scope string * Defines the scope in which this map is allowed, 'selector' for selector renaming, 'url' for url updates and '*' for both.
ignoreCase boolean true Indicates if the search is case-insensitive or not.
greedy boolean options.greedy When enabled, string replacement will NOT respect word boundaries. i.e. .ultra { ...} will be changed to .urtla {...}


// a simple map, for swapping "prev" with "next" and vice versa. 
  "name"    : "prev-next",
  "search"  : "prev",
  "replace" : "next"
// a more detailed version, considering the convention used in the authored CSS document. 
  "name"    : "prev-next",
  "search"  : ["prev", "Prev", "PREV"],
  "replace" : ["next", "Next", "NEXT"],
  options   : {"ignoreCase":false}

Array of plugins to add more functionality to RTLCSS, or even change it's entire behavior. See Writing an RTLCSS Plugin.

Have a bug or a feature request? please feel free to open a new issue .

To view changes in recent versions, see the CHANGELOG.