CSS Code Quality calculator

---

This package analyzes your CSS on a high level and comes up with a score, divided into three areas:

• Maintainability: how difficult is it for someone looking at the CSS from a high level to find the exact spot to fix a bug?
• Complexity: how difficult is it for someone to make a change and be confident that they can make that change without side effects?
• Performance: How likely is the CSS to have a negative impact on performance, based on high-level metrics? (Not including using hardware accelerated transforms and the like, because other tools are more suited for that.)

Installation

npm install @projectwallace/css-code-quality

Usage

import { calculate } from '@projectwallace/css-code-quality'

let css = `my_css { /* ... */ }`
let result = calculate(css)

/*
The result shape looks something like this:

{
  "violations": [ ],
  "passes": [ ],
  "performance": {
    "score": 90,
    "violations": [ ],
    "passes": [ ]
  },
  "maintainability": {
    "score": 100,
    "violations": [ ],
    "passes": [ ]
  },
  "complexity": {
    "score": 97,
    "violations": [ ],
    "passes": [ ]
  }
}

Each `passes` or `violations` array contains an object that looks like this:

{
  "id": "EmptyRules",
  "score": 0,
  "value": 0
},
{
  "id": "AverageSelectorsPerRule",
  "score": 0,
  "value": 1.5,
  "actuals": [
    2,
    1
  ]
}

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 - A CSS Analyzer that goes through your CSS to find all kinds of relevant statistics.
• Wallace CLI - CLI tool for @projectwallace/css-analyzer
• Constyble - CSS Complexity linter
• Color Sorter - Sort CSS colors by hue, saturation, lightness and opacity