diff --git a/readme.md b/readme.md
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+++ b/readme.md
@@ -87,6 +87,43 @@ etc. etc.
 */
 ```
 
+## Metrics
+
+### Performance
+
+| Metric                    | What is tested                               | Points deducted                             |
+| ------------------------- | -------------------------------------------- | ------------------------------------------- |
+| `Imports`                 | Number of `@import` rules                    | 10 per `@import`                            |
+| `EmptyRules`              | Number of empty rules                        | 1 per empty rule                            |
+| `SelectorDuplications`    | Ratio of duplicate selectors                 | Up to 10 (when uniqueness ratio < 66%)      |
+| `DeclarationDuplications` | Ratio of duplicate declarations              | Up to 10 (when uniqueness ratio < 66%)      |
+| `CssSize`                 | Total CSS file size                          | 5 if size exceeds 200,000 bytes             |
+| `TooMuchComments`         | Total size of comments                       | 1 per 250 bytes of comments, max 10         |
+| `TooMuchEmbeddedContent`  | Total size of embedded content (e.g. base64) | 1 per 250 bytes of embedded content, max 20 |
+
+### Maintainability
+
+| Metric                                  | What is tested                                               | Points deducted                                             |
+| --------------------------------------- | ------------------------------------------------------------ | ----------------------------------------------------------- |
+| `SourceLinesOfCode`                     | Total source lines of code                                   | 1 per 1,000 lines over 10,000, max 15                       |
+| `AverageSelectorsPerRule`               | Average number of selectors per rule                         | 5 per selector over 2 (average), max 15                     |
+| `AverageDeclarationsPerRule`            | Average number of declarations per rule                      | 5 per declaration over 5 (average), max 15                  |
+| `MaxSelectorsPerRule`                   | Maximum number of selectors in a single rule                 | 0.5 per selector over 10, max 15                            |
+| `MaxDeclarationsPerRule`                | Maximum number of declarations in a single rule              | 0.5 per declaration over 10, max 15                         |
+| `MoreThanMostCommonSelectorsPerRule`    | Rules that have more selectors than the most common count    | 0.01 per rule, max 15 (when > 10% of rules exceed the mode) |
+| `MoreThanMostCommonDeclarationsPerRule` | Rules that have more declarations than the most common count | 0.01 per rule, max 15 (when > 10% of rules exceed the mode) |
+
+### Complexity
+
+| Metric                                  | What is tested                                                     | Points deducted                                                     |
+| --------------------------------------- | ------------------------------------------------------------------ | ------------------------------------------------------------------- |
+| `MoreThanMostCommonSelectorComplexity`  | Selectors more complex than the most common complexity             | 0.01 per selector, max 10 (when > 10% of selectors exceed the mode) |
+| `MoreThanMostCommonSelectorSpecificity` | Selectors with higher specificity than the most common specificity | 0.01 per selector, max 10 (when > 10% of selectors exceed the mode) |
+| `MaxSelectorComplexity`                 | Maximum complexity of a single selector                            | 0.5 per complexity unit over 5, max 5                               |
+| `AverageSelectorComplexity`             | Average selector complexity                                        | 2 per complexity unit over 2 (average), max 10                      |
+| `IdSelectorRatio`                       | Ratio of ID selectors                                              | Up to 5 (when ID selector ratio exceeds 1%)                         |
+| `ImportantRatio`                        | Ratio of `!important` declarations                                 | Up to 5 (when `!important` ratio exceeds 1%)                        |
+
 ## Related projects
 
 - [CSS Analyzer](https://github.com/projectwallace/css-analyzer) -