--- /dev/null
+# PostCSS Plugin Guidelines
+
+A PostCSS plugin is a function that receives and, usually,
+transforms a CSS AST from the PostCSS parser.
+
+The rules below are *mandatory* for all PostCSS plugins.
+
+See also [ClojureWerkz’s recommendations] for open source projects.
+
+[ClojureWerkz’s recommendations]: http://blog.clojurewerkz.org/blog/2013/04/20/how-to-make-your-open-source-project-really-awesome/
+
+## 1. API
+
+### 1.1 Clear name with `postcss-` prefix
+
+The plugin’s purpose should be clear just by reading its name.
+If you wrote a transpiler for CSS 4 Custom Media, `postcss-custom-media`
+would be a good name. If you wrote a plugin to support mixins,
+`postcss-mixins` would be a good name.
+
+The prefix `postcss-` shows that the plugin is part of the PostCSS ecosystem.
+
+This rule is not mandatory for plugins that can run as independent tools,
+without the user necessarily knowing that it is powered by
+PostCSS — for example, [cssnext] and [Autoprefixer].
+
+[Autoprefixer]: https://github.com/postcss/autoprefixer
+[cssnext]: http://cssnext.io/
+
+### 1.2. Do one thing, and do it well
+
+Do not create multitool plugins. Several small, one-purpose plugins bundled into
+a plugin pack is usually a better solution.
+
+For example, [cssnext] contains many small plugins,
+one for each W3C specification. And [cssnano] contains a separate plugin
+for each of its optimization.
+
+[cssnext]: http://cssnext.io/
+[cssnano]: https://github.com/ben-eb/cssnano
+
+### 1.3. Do not use mixins
+
+Preprocessors libraries like Compass provide an API with mixins.
+
+PostCSS plugins are different.
+A plugin cannot be just a set of mixins for [postcss-mixins].
+
+To achieve your goal, consider transforming valid CSS
+or using custom at-rules and custom properties.
+
+[postcss-mixins]: https://github.com/postcss/postcss-mixins
+
+### 1.4. Create plugin by `postcss.plugin`
+
+By wrapping your function in this method,
+you are hooking into a common plugin API:
+
+```js
+module.exports = postcss.plugin('plugin-name', function (opts) {
+ return function (css, result) {
+ // Plugin code
+ };
+});
+```
+
+## 2. Processing
+
+### 2.1. Plugin must be tested
+
+A CI service like [Travis] is also recommended for testing code in
+different environments. You should test in (at least) Node.js 0.12 and stable.
+
+[Travis]: https://travis-ci.org/
+
+### 2.2. Use asynchronous methods whenever possible
+
+For example, use `fs.writeFile` instead of `fs.writeFileSync`:
+
+```js
+postcss.plugin('plugin-sprite', function (opts) {
+ return function (css, result) {
+
+ return new Promise(function (resolve, reject) {
+ var sprite = makeSprite();
+ fs.writeFile(opts.file, function (err) {
+ if ( err ) return reject(err);
+ resolve();
+ })
+ });
+
+ };
+});
+```
+
+### 2.3. Set `node.source` for new nodes
+
+Every node must have a relevant `source` so PostCSS can generate
+an accurate source map.
+
+So if you add new declaration based on some existing declaration, you should
+clone the existing declaration in order to save that original `source`.
+
+```js
+if ( needPrefix(decl.prop) ) {
+ decl.cloneBefore({ prop: '-webkit-' + decl.prop });
+}
+```
+
+You can also set `source` directly, copying from some existing node:
+
+```js
+if ( decl.prop === 'animation' ) {
+ var keyframe = createAnimationByName(decl.value);
+ keyframes.source = decl.source;
+ decl.root().append(keyframes);
+}
+```
+
+### 2.4. Use only the public PostCSS API
+
+PostCSS plugins must not rely on undocumented properties or methods,
+which may be subject to change in any minor release. The public API
+is described in [API docs].
+
+[API docs]: https://github.com/postcss/postcss/blob/master/docs/api.md
+
+## 3. Errors
+
+### 3.1. Use `node.error` on CSS relevant errors
+
+If you have an error because of input CSS (like an unknown name
+in a mixin plugin) you should use `node.error` to create an error
+that includes source position:
+
+```js
+if ( typeof mixins[name] === 'undefined' ) {
+ throw decl.error('Unknown mixin ' + name, { plugin: 'postcss-mixins' });
+}
+```
+
+### 3.2. Use `result.warn` for warnings
+
+Do not print warnings with `console.log` or `console.warn`,
+because some PostCSS runner may not allow console output.
+
+```js
+if ( outdated(decl.prop) ) {
+ result.warn(decl.prop + ' is outdated', { node: decl });
+}
+```
+
+If CSS input is a source of the warning, the plugin must set the `node` option.
+
+## 4. Documentation
+
+### 4.1. Document your plugin in English
+
+PostCSS plugins must have their `README.md` written in English. Do not be afraid
+of your English skills, as the open source community will fix your errors.
+
+Of course, you are welcome to write documentation in other languages;
+just name them appropriately (e.g. `README.ja.md`).
+
+### 4.2. Include input and output examples
+
+The plugin's `README.md` must contain example input and output CSS.
+A clear example is the best way to describe how your plugin works.
+
+The first section of the `README.md` is a good place to put examples.
+See [postcss-opacity](https://github.com/iamvdo/postcss-opacity) for an example.
+
+Of course, this guideline does not apply if your plugin does not
+transform the CSS.
+
+### 4.3. Maintain a changelog
+
+PostCSS plugins must describe the changes of all their releases
+in a separate file, such as `CHANGELOG.md`, `History.md`, or [GitHub Releases].
+Visit [Keep A Changelog] for more information about how to write one of these.
+
+Of course, you should be using [SemVer].
+
+[Keep A Changelog]: http://keepachangelog.com/
+[GitHub Releases]: https://help.github.com/articles/creating-releases/
+[SemVer]: http://semver.org/
+
+### 4.4. Include `postcss-plugin` keyword in `package.json`
+
+PostCSS plugins written for npm must have the `postcss-plugin` keyword
+in their `package.json`. This special keyword will be useful for feedback about
+the PostCSS ecosystem.
+
+For packages not published to npm, this is not mandatory, but is recommended
+if the package format can contain keywords.
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