linter

Linters

Below is a list of linters supported by scss-lint, ordered alphabetically.

• BangFormat
• BemDepth
• BorderZero
• ChainedClasses
• ColorKeyword
• ColorVariable
• Comment
• Compass Linters
• DebugStatement
• DeclarationOrder
• DisableLinterReason
• DuplicateProperty
• ElsePlacement
• EmptyLineBetweenBlocks
• EmptyRule
• ExtendDirective
• FinalNewline
• HexLength
• HexNotation
• HexValidation
• IdSelector
• ImportantRule
• ImportPath
• Indentation
• LeadingZero
• LengthVariable
• MergeableSelector
• NameFormat
• NestingDepth
• PlaceholderInExtend
• PrivateNamingConvention
• PropertyCount
• PropertySortOrder
• PropertySpelling
• PropertyUnits
• PseudoElement
• QualifyingElement
• SelectorDepth
• SelectorFormat
• Shorthand
• SingleLinePerProperty
• SingleLinePerSelector
• SpaceAfterComma
• SpaceAfterPropertyColon
• SpaceAfterPropertyName
• SpaceAfterVariableColon
• SpaceAfterVariableName
• SpaceAroundOperator
• SpaceBeforeBrace
• SpaceBetweenParens
• StringQuotes
• TrailingSemicolon
• TrailingWhitespace
• TrailingZero
• TransitionAll
• UnnecessaryMantissa
• UnnecessaryParentReference
• UrlFormat
• UrlQuotes
• VariableForProperty
• VendorPrefix
• ZeroUnit

BangFormat

Reports when you use improper spacing around ! (the "bang") in !default, !global, !important, and !optional flags.

You can prefer a single space or no space both before and after the !.

Bad

color: #000!important;

Good

color: #000 !important;

Configuration Option	Description
space_before_bang	Whether a space should be present before the !, as in color: #000 !important; (default true)
space_after_bang	Whether a space should be present after the !, as in color: #000 ! important; (default false)

BemDepth

Disabled by default

Reports when a BEM selector contains more elements than a configurable maximum number.

Bad

.block__element__subelement  {
  ...
}

Good

.block__element {
  ...
}

Configuration Option	Description
max_elements	Maximum number of elements allowed in a BEM selector (default 1)

BorderZero

Prefer the terser border: 0 over border: none.

You can specify preferring border: none over border: 0 by setting the convention option.

Configuration Option	Description
convention	Whether to prefer 0 (zero) or none (none) (default zero)

ChainedClasses

Disabled by default

Reports when you define a rule set using a selector with chained classes (a.k.a. adjoining classes).

Bad

.foo {
  padding: 5px;
}

.bar {
  margin: 5px;
}

.foo.bar {
  display: block;
}

Good: write chained classes as new class

.foo {
  padding: 5px;
}

.bar {
  margin: 5px;
}

.new-class {
  display: block;
}

ColorKeyword

Prefer hexadecimal color codes over color keywords.

Bad: color keyword

color: green;

Good: hexadecimal color

color: #0f0;

Color keywords look like variables but are not variables. See the ColorVariable linter for more justification on why you should always refer to colors via variables.

ColorVariable

Prefer color literals (keywords or hexadecimal codes) to be used only in variable declarations. They should be referred to via variables everywhere else.

Bad: literal color

p {
  color: green;
}

Good: refer to color by variable name

$body-color: #0f0;

...

p {
  color: $body-color;
}

Defining colors directly in properties is usually a smell. When you color your body text in a number of places, if you ever want to change the color of the text you'll have to update the explicitly defined color in a number of places, and finding all those places can be difficult if you use the same color for other elements (i.e. a simple find/replace may not always work).

A better approach is to use global variables like $color-text-body and refer to this variable everywhere you want to use it. This makes it easy to update the color, as you only need change it in one place. It is also more intention-revealing, as seeing the name $color-text-body is more descriptive than #333 or black. Using color keywords can obfuscate this, as they look like variables.

Comment

Prefer // comments over /* ... */.

Bad

/* This is a comment that gets rendered */

Good

// This comment never gets rendered

// comments should be preferred as they don't get rendered in the final generated CSS, whereas /* ... */ comments do.

Furthermore, comments should be concise, and using /* ... */ encourages multi-line comments which tend to not be concise.

If you want to allow multi-line comments containing certain text, such as copyright notices, set the allowed option to a regular expression. This will allow multi-line comments that match the regular expression.

Configuration Option	Description
allowed	Regular expression for matching allowed comments, such as '^[/* ] Copyright'
style	Style of comment to enforce (silent or loud) (default silent)

Compass Linters

scss-lint includes a set of linters for codebases which use the Compass framework.

###» Compass Linters Documentation

DebugStatement

Reports @debug statements (which you probably left behind accidentally).

DeclarationOrder

Rule sets should be ordered as follows: @extend declarations, @include declarations without inner @content, properties, @include declarations with inner @content, then nested rule sets.

Bad

.fatal-error {
  p {
    ...
  }

  color: #f00;
  @extend %error;
  @include message-box();
}

Good

.fatal-error {
  @extend %error;
  @include message-box();
  color: #f00;

  p {
    ...
  }
}

The @extend statement functionally acts like an inheritance mechanism, which means the properties defined by the placeholder being extended are rendered before the rest of the properties in the rule set.

Thus, declaring the @extend at the top of the rule set reminds the developer of this behavior.

Placing @include declarations without inner @content before properties serves to group them with @extend declarations and provides the opportunity to overwrite them later in the rule set.

@includes with inner @content often involve @media rules that rely on the cascade or nested rule sets, which justifies their inclusion after regular properties.

Mixin @content and nested rule sets are also linted for declaration order.

DisableLinterReason

Disabled by default

scss-lint:disable control comments should be preceded by a comment explaining why these linters are being disabled for this file.

Bad

// scss-lint:disable BorderZero
p {
  border: none;
}

Good

// We really prefer `border: none` in this file, for reasons.
// scss-lint:disable BorderZero
p {
  border: none;
}

DuplicateProperty

Reports when you define the same property twice in a single rule set.

Bad

h1 {
  margin: 10px;
  text-transform: uppercase;
  margin: 0; // Second declaration
}

Having duplicate properties is usually just an error. However, they can be used as a technique for dealing with varying levels of browser support for CSS properties. In the example below, some browsers might not support the rgba function, so the intention is to fall back to the color #fff.

.box {
  background: #fff;
  background: rgba(255, 255, 255, .5);
}

In this situation, using duplicate properties is acceptable, but you will have to configure DuplicateProperty with the ignore_consecutive option, so that it won't consider such cases to be lint. ignore_consecutive can be set to true, false (default), or a list of property names to be allowed. For example, to ignore consecutive background and transition properties, as above, you can configure DuplicateProperty with:

DuplicateProperty:
  ignore_consecutive:
    - background
    - transition

Configuration Option	Description
ignore_consecutive	Whether to ignore consecutive duplicate properties (default false), or a whitelist.

ElsePlacement

Place @else statements on the same line as the preceding curly brace.

Bad

@if {
  ...
}
@else {
  ...
}

Good

@if {
  ...
} @else {
  ...
}

This will ignore single line @if/@else blocks, so you can write:

@if { ... } @else { ... }

You can prefer to enforce having @else on its own line by setting the style configuration option to new_line.

Configuration Option	Description
style	same_line or new_line (default same_line)

EmptyLineBetweenBlocks

Separate rule, function, and mixin declarations with empty lines.

Bad: no lines separating blocks

p {
  margin: 0;
  em {
    ...
  }
}
a {
  ...
}

Good: lines separating blocks

p {
  margin: 0;

  em {
    ...
  }
}

a {
  ...
}

By default, this will ignore single line blocks, so you can write:

.icon-chevron-up    { &:before { content: "\e030"; } }
.icon-chevron-down  { &:before { content: "\e031"; } }
.icon-chevron-left  { &:before { content: "\e032"; } }
.icon-chevron-right { &:before { content: "\e033"; } }

Configuration Option	Description
ignore_single_line_blocks	Don't enforce for single-line blocks (default true)

EmptyRule

Reports when you have an empty rule set.

.cat {
}

ExtendDirective

Disabled by default

Reports when you have an @extend directive.

p {
  @extend %placeholder;
}

If you want to restrict the @extend directive to only use placeholders, see the PlaceholderInExtend linter instead.

FinalNewline

Files should always have a final newline. This results in better diffs when adding lines to the file, since SCM systems such as git won't think that you touched the last line.

You can customize whether or not a final newline exists with the present option.

Configuration Option	Description
present	Whether a final newline should be present (default true)

HexLength

You can specify whether you prefer shorthand or long-form hexadecimal colors by setting the style option to short or long, respectively.

short

color: #f2e;

long

color: #ff22ee;

Configuration Option	Description
style	Prefer short or long (default short)

HexNotation

Checks if hexadecimal colors are written in lowercase. You can specify which case with the style option.

Configuration Option	Description
style	Prefer lowercase or uppercase (default lowercase)

HexValidation

Ensure hexadecimal colors are valid (either three or six digits).

Bad

p {
  background: #ab; // Clearly a typo
}

Good

p {
  background: #abc;
}

IdSelector

Avoid using ID selectors.

Bad: highly-specific styling for a single element via ID

#submit-button {
  ...
}

Good: reusable class

.submit-button {
  ...
}

While the CSS specification allows for multiple elements with the same ID to appear in a single document, in practice this is a smell. ID selectors should never be used for the purposes of styling an element, as it leads to overly specific styles that aren't easily shared with other elements.

ImportantRule

Avoid using !important in properties. It is usually indicative of a misunderstanding of CSS specificity and can lead to brittle code.

Bad

p {
  color: #f00 !important;
}

Good

p {
  color: #f00;
}

ImportPath

The basenames of @imported SCSS partials should not begin with an underscore and should not include the filename extension.

Bad

@import "foo/_bar.scss";
@import "_bar.scss";
@import "_bar";
@import "bar.scss";

Good

@import "foo/bar";
@import "bar";

You can configure this linter to instead ensure that you do include the leading underscore or the filename extension by setting either option to true. Being explicit might have its place, as long as you are consistent.

@import declarations that Sass compiles directly into CSS @import rules will be ignored.

Configuration Option	Description
leading_underscore	false or true (default false)
filename_extension	false or true (default false)

Indentation

Use two spaces per indentation level.

Bad: four spaces

p {
    color: #f00;
}

Good: two spaces

p {
  color: #f00;
}

You can configure this linter to prefer tabs if you like.

For projects that follow BEM, you may prefer to allow arbitrary indentation for rule sets that aren't nested in order to give the visual hints of hierarchy without actually nesting selectors (which has a performance cost). For example:

.component {}
  .component__image {}
  .component__text {}
    .component-subblock {}
    .component-subblock__text {}
  .component-category {}
    .component-other {}

You can set allow_non_nested_indentation to true if this convention is preferred.

Configuration Option	Description
allow_non_nested_indentation	Whether non-nested rule sets can be arbitrarily indented (default false)
character	tab or space (default space)
width	Number of characters per indentation level (default 2)

LeadingZero

Don't write leading zeros for numeric values with a decimal point.

Bad: unnecessary leading zero

margin: 0.5em;

Good: no leading zero

margin: .5em;

You can configure this to prefer including leading zeros.

Configuration Option	Description
style	exclude_zero or include_zero (default exclude_zero)

LengthVariable

Prefer length literals (numbers with units) to be used only in variable declarations. They should be referred to via variables, or calculations using variables, everywhere else.

Bad: literal length

div {
  width: 100px;
}

Good: refer to length by variable name

$column-width: 100px;

...

div {
  width: $column-width;
}

Most lengths in stylesheets are related to and dependant on other lengths. By only using variables you are forced to name these lengths and relate them to each other. This linter does not catch uses of percentages as those size relationships are already present. It encourages calculations: e.g -$input-height or $input-height - $input-line-weight * 2.

Defining length directly in properties usually leads to future magic-number detective work. For example, if you ever want to change the height of all form inputs then you'll have to update the heights and widths and margins of many things in a number of places, and finding all those places can be difficult if you use the same length for other things, or you have values that are related to other values (e.g. the height minus the border width). A simple find/ replace may not always work.

A better approach is to use global variables like $standard-input-height and refer to this variable everywhere you want to use it. This makes it easy to update the color, as you only need change it in one place. It is also more intention-revealing, as seeing the name $input-height is more descriptive than 40px or 1.5em.

Limitations

• This doesn't catch width: $button-width + 2 where the 2 is implicitly 2px. SASS is too clever here.
• This doesn't flag length literals that are percentages: 1. because that already expresses how lengths are related to each other, and 2. because percentages are also used for non-length values. (e.g. fade-out(black, 70%))

Configuration Option	Description
allowed_lengths	A list of lengths (numbers with units) that aren't caught. e.g. [100vh, 100vw]
allowed_properties	A list of properties that can use literal lengths, e.g. [text-shadow, box-shadow]

MergeableSelector

Reports when you define the same selector twice in a single sheet.

Bad

h1 {
  margin: 10px;
}

.baz {
  color: red;
}

// Second copy of h1 rule
h1 {
  text-transform: uppercase;
}

Good

h1 {
  margin: 10px;
  text-transform: uppercase;
}

.baz {
  color: red;
}

Combining duplicate selectors can result in an easier to read sheet, but occasionally the rules may be purposely duplicated to set precedence after a rule with the same CSS specificity. However, coding your stylesheets in this way makes them more difficult to comprehend, and can usually be avoided.

You can specify that rule sets which can be nested within another rule set must be nested via the force_nesting option, e.g.

Bad

h1 {
  color: #fff;
}

h1.new {
  color: #000;
}

Good

h1 {
  color: #fff;

  &.new {
    color: #000;
  }
}

Configuration Option	Description
force_nesting	Ensure rule sets which can be nested are nested (default true)
whitelist	A list of selectors that can MergeableSelector, list those used in CSS Shims

NameFormat

Functions, mixins, variables, and placeholders should be declared with all lowercase letters and hyphens instead of underscores.

Bad: uppercase characters

$myVar: 10px;

@mixin myMixin() {
  ...
}

Good: all lowercase with hyphens

$my-var: 10px;

@mixin my-mixin() {
  ...
}

The Sass parser automatically treats underscores and hyphens the same, so even if you're using a library that declares a function with an underscore, you can refer to it using the hyphenated form instead.

Depending on whether you use underscores to denote private functions within your code, you can set the allow_leading_underscore option (enabled by default) which will ignore leading underscores in names if they exist, allowing declarations like @function _private-function() { ... }. If you want to further enforce a private naming convention, use PrivateNamingConvention.

Configuration Option	Description
allow_leading_underscore	Whether to allow names to start with a single underscore (default true)
convention	Name of convention to use (hyphenated_lowercase (default), camel_case, snake_case), or a regex the name must match (eg: ^[a-zA-Z]+$)
convention_explanation	Custom catch-all explanation if you do not want to use the built-in explanations
{type}_convention	Convention to use for {type}s, where {type} is on of function, mixin, variable, or placeholder
{type}_convention_explanation	Custom explanation for {type} convention, where {type} is one of function, mixin, variable, or placeholder

NestingDepth

Avoid nesting selectors too deeply.

Bad: deeply nested

.one {
  .two {
    .three {
      .four {
        ...
      }
    }
  }
}

Good

.three:hover {
}

.three {
  &:hover {
    ...
  }
}

Overly nested rules will result in over-qualified CSS that could prove hard to maintain, output unnecessary selectors and is generally considered bad practice.

This linter will not report an error if you have selectors with a large depth of applicability. Use SelectorDepth for this purpose.

No error

.one .two .three {
  ...
}

Error

.one {
  .two {
    .three {
      ...
    }
  }
}

Configuration Option	Description
max_depth	Maximum depth before reporting errors (default 3)
ignore_parent_selectors	Whether to report errors for parent selectors (default false)

PlaceholderInExtend

Always use placeholder selectors in @extend.

Bad: extending a class

.fatal {
  @extend .error;
}

Good: extending a placeholder

.fatal {
  @extend %error;
}

Using a class selector with the @extend directive usually results in more generated CSS than when using a placeholder selector. Furthermore, Sass specifically introduced placeholder selectors in order to be used with @extend.

See Mastering Sass extends and placeholders.

If you want to prevent the use of the @extend directive entirely, see the ExtendDirective linter.

PrivateNamingConvention

Disabled by default

Enforces that functions, mixins, and variables that follow the private naming convention (default to underscore-prefixed, e.g. $_foo) are defined and used within the same file.

Bad

$_foo: #f00;

p {
  color: #00f;
}

Bad

p {
  color: $_foo;
}

Bad

p {
  color: $_foo;
}

$_foo: #f00;

Good

$_foo: #f00;

p {
  color: $_foo;
}

Configuration Option	Description
prefix	Prefix used to denote "private" (default _)

PropertyCount

Disabled by default

Limit the number of properties in a rule set.

Specifying a large number of properties in a rule set is usually an opportunity to break down the rule set into smaller more reusable components. It is also a sign that you might not be leveraging the true power of the "cascade", as you are explicitly defining a large number of properties many times.

Bad: large number of properties

.class {
  color: #f00;
  font: 15px arial, sans-serif;
  margin: 0;
  padding: 0;
}

Good: small number of properties

.class {
  margin: 0;
  padding: 0;
}

You can specify that the count of properties include properties in nested rule sets via the include_nested option. This is useful if you care about the overall complexity of a generated rule set, rather than just each individual set.

Configuration Option	Description
include_nested	Whether to include the properties in nested rule sets in the count
max_properties	Maximum number of properties

PropertySortOrder

Sort properties in a strict order. By default, will require properties be sorted in alphabetical order, as it's brain dead simple (highlight lines and execute :sort in vim), and it can benefit gzip compression.

You can also specify an explicit ordering via the order option, which allows you to specify an explicit array of properties representing the preferred order, or the name of a preset order. If a property is not in your explicit list, it will be placed at the bottom of the list, disregarding its order relative to other unspecified properties.

For example, to define a custom sort order, you can write:

linters:
  PropertySortOrder:
    order:
      - display
      - margin
      - etc...

Or you can use a preset order by writing:

linters:
  PropertySortOrder:
    order: concentric

You can enforce that "groups" of properties be visually separated by setting the separate_groups option to true. When specifying a custom order, you can indicate that you want two groups of properties to be visually separate by inserting an empty item, e.g.

linters:
  PropertySortOrder:
    order:
      - display
      - position
      -            # This empty element signals a visual separation
      - margin
      - padding
    separate_groups: true

This would result in the following separation being enforced:

p {
  display: block;
  position: absolute;

  margin: 0;
  padding: 0;
}

Note that separate_groups is only enforced if a custom order is specified via the order option. Also note that if ignore_unspecified is true then properties which are "ignored" are considered as visual separators.

If you need to write vendor-prefixed properties, the linter will allow you to order the vendor-prefixed properties before the standard CSS property they apply to. For example:

border: 0;
-moz-border-radius: 3px;
-o-border-radius: 3px;
-webkit-border-radius: 3px;
border-radius: 3px;
color: #ccc;
margin: 5px;

In this case, this is usually avoided by using mixins from a framework like Compass or Bourbon so vendor-specific properties rarely need to be explicitly written by hand.

If you are specifying an explicit order for properties, note that vendor-prefixed properties will still be ordered based on the example above (i.e. you only need to specify normal properties in your list).

Configuration Option	Description
ignore_unspecified	Whether to ignore properties that are not explicitly specified in order (default false)
min_properties	Minimum number of sortable properties (i.e. properties which are defined by the given order) present in the rule set before linting takes place (default 2)
order	Array of properties, or the name of a preset order (default is nil, resulting in alphabetical ordering)
separate_groups	Whether gaps between groups of properties should be enforced.

PropertySpelling

Reports when you use an unknown or disabled CSS property (ignoring vendor-prefixed properties).

diplay: none; // "display" is spelled incorrectly

Since the list of available CSS properties is constantly changing, it's possible that you might get some false positives here, especially if you're using experimental CSS features. If that's the case, you can add additional properties to the whitelist by adding the following to your .scss-lint.yml configuration:

linters:
  PropertySpelling:
    extra_properties:
      - some-experimental-property
      - another-experimental-property
    disabled_properties:
      - some-existing-property
      - another-existing-property

If you're sure the property in question is valid, submit a request to add it to the default whitelist.

Configuration Option	Description
extra_properties	List of extra properties to allow
disabled_properties	List of existing properties to deny

PropertyUnits

Configure which units are allowed for property values.

By default a value may have any kind of unit. You can adjust which units are allowed globally by setting the global option. Alternately, you can specify a list of units for a single property by adding it to the properties option, e.g.

PropertyUnits:
  global: ['em', 'rem', '%'] # Allow relative units globally
  properties:
    border: ['px'] # Only pixels
    line-height: [] # No units allowed
    margin: ['em', 'rem']

With the above configuration, the following issues would be reported:

p {
  border: 1rem solid blue; // rem not in `border` list
  line-height: 55px; // px not in `line-height` list
  padding: 10px; // px not in `global` list
  margin: 10%; // % not in `margin` list
}

Configuration Option	Description
global	List of allowed units (by default any unit is allowed)
properties	Hash of property names and their list of allowed units. (empty by default)

PseudoElement

Pseudo-elements, like ::before, and ::first-letter, should be declared with two colons. Pseudo-classes, like :hover and :first-child, should be declared with one colon.

If you're sure the pseudo-element in question is valid, submit a request to add it to the default whitelist.

Bad: wrong colons

p:before {
  content: '>'
}

p::hover {
  color: red;
}

Good: correct colons

p::before {
  content: '>'
}

p:hover {
  color: red;
}

QualifyingElement

Avoid qualifying elements in selectors (also known as "tag-qualifying").

Bad: qualifying elements

div#thing {
  ...
}

ul.list {
  ...
}

ul li.item {
  ...
}

a[href="place"] {
  ...
}

Good

#thing {
  ...
}

.list {
  ...
}

ul .item {
  ...
}

[href="place"] {
  ...
}

Since IDs are unique, they will not apply to multiple elements, so there is no good reason to qualify an ID selector with an element.

In most cases, qualifying a class or attribute selector with an element adds unnecessary or undesirable specificity. Often the element qualifier is already superfluous; and if it is not, you will probably be better off refactoring so that it can be removed.

Use the options to allow certain qualifying elements.

Configuration Option	Description
allow_element_with_attribute	Allow elements to qualify attributes (default false)
allow_element_with_class	Allow elements to qualify classes (default false)
allow_element_with_id	Allow elements to qualify ids (default false)

SelectorDepth

Don't write selectors with a depth of applicability greater than 3.

Bad: selectors with depths of 4

.one .two .three > .four {
  ...
}

.one .two {
  .three > .four {
    ...
  }
}

Good

.one .two .three {
  ...
}

.one .two {
  .three {
    ...
  }
}

Selectors with a large depth of applicability lead to CSS tightly-coupled to your HTML structure, making it brittle to change.

Deep selectors also come with a performance penalty, which can affect rendering times, especially on mobile devices. While the default limit is 3, ideally it is better to use less than 3 whenever possible.

Configuration Option	Description
max_depth	Maximum depth before reporting errors (default 3)

SelectorFormat

It is good practice to choose a convention for naming selectors.

Good

// convention: 'hyphenated_lowercase'
.foo-bar-77, foo-bar, #foo-bar {}

// convention: 'snake_case'
.foo_bar77, foo_bar, #foo_bar {}

// convention: 'camel_case'
.fooBar77, fooBar, #fooBar {}
}

You can specify different conventions for different types of selectors using the [type]_convention options.

Since you might need to overwrite selectors for third party stylesheets, you can specify ignored_names as an array of individual selectors to ignore. Another option is to specify ignored_types to globally ignore a certain type of selector.

Configuration Option	Description
convention	Name of convention to use (hyphenated_lowercase (default) or snake_case, camel_case, or strict_BEM, or hyphenated_BEM), or a regex the name must match. Note: If your project uses BEM, pay attention to the dialect of BEM you use. It may be strict_BEM or hyphenated_BEM.
convention_explanation	Custom catch-all explanation if you do not want to use the built-in explanations
ignored_names	Array of whitelisted names to not report lints for.
ignored_types	Array containing list of types of selectors to ignore (valid values are attribute, class, element, id, placeholder)
{type}_convention	Convention for {type} selectors only, where {type} is one of attribute, class, id, or placeholder. See the convention option for possible values.
{type}_convention_explanation	Custom explanation for {type} selector convention, where {type} is one of attribute, class, id, or placeholder.

Limitations

SelectorFormat will not resolve the parent selector reference (&), and will ignore selectors containing any parent references. This is because these references cannot be resolved without compiling the Sass into actual CSS. If you would like to see such functionality, we'd love to merge a pull request!

Shorthand

Prefer the shortest shorthand form possible for properties that support it.

Bad: all 4 sides specified with same value

margin: 1px 1px 1px 1px;

Good: equivalent to specifying 1px for all sides

margin: 1px;

If you don't want to allow all possible shorthands, you can limit them by setting the allowed_shorthands array option to a subset of [1, 2, 3, 4].

Configuration Option	Description
allowed_shorthands	Array of allowed shorthand lengths (default [1, 2, 3, 4])

SingleLinePerProperty

Properties within rule sets should each reside on their own line.

Bad

p {
  margin: 0; padding: 0;
}

Good

p {
  margin: 0;
  padding: 0;
}

A special exception is made for single line rule sets. For example the following is acceptable:

p { margin: 0; padding: 0; }

If you want to also report a lint for single line rule sets, set the allow_single_line_rule_sets option to false.

Configuration Option	Description
allow_single_line_rule_sets	true or false (default true)

SingleLinePerSelector

Split selectors onto separate lines after each comma, and have each individual selector occupy a single line.

Bad: comma-separated selectors not on their own lines

.error p, p.explanation {
  ...
}

Bad: descendent selector spread over multiple lines

.error
  p,
  p.explanation {
  ...
}

Good: each selector sequence is on its own individual line

.error p,
p.explanation {
  ...
}

Note that selectors containing interpolation are ignored, since the Sass parser cannot construct the selector parse tree at parse time, only at run time (which is too late for scss-lint to do anything with).

SpaceAfterComma

Commas in lists should be followed by a space.

Bad: no space after commas

@include box-shadow(0 2px 2px rgba(0,0,0,.2));
color: rgba(0,0,0,.1);

Good: commas followed by a space

@include box-shadow(0 2px 2px rgba(0, 0, 0, .2));
color: rgba(0, 0, 0, .1);

The style option allows you to specify a different preferred style.

Configuration Option	Description
style	one_space, or no_space or at_least_one_space (default one_space)

SpaceAfterPropertyColon

Properties should be formatted with a single space separating the colon from the property's value.

Bad: no space after colon

margin:0;

Bad: more than one space after colon

margin:  0;

Good

margin: 0;

The style option allows you to specify a different preferred style.

Configuration Option	Description
style	one_space, no_space, at_least_one_space, one_space_or_newline, or aligned (default one_space)

SpaceAfterPropertyName

Properties should be formatted with no space between the name and the colon.

Bad: space before colon

margin : 0;

Good

margin: 0;

SpaceAfterVariableColon

Variables should be formatted with a single space separating the colon from the variable's value.

Bad: no space after colon

$my-color:#fff;

Bad: more than one space after colon

$my-color:  #fff;

Good

$my-color: #fff;

The style option allows you to specify a different preferred style.

Configuration Option	Description
style	one_space, no_space, at_least_one_space or one_space_or_newline (default one_space)

SpaceAfterVariableName

Variables should be formatted with no space between the name and the colon.

Bad: space before colon

$my-var : 0;

Good

$my-var: 0;

SpaceAroundOperator

Operators should be formatted with a single space on both sides of an infix operator. These include +, -, *, /, %, ==, !=, >, >=, <, and <=.

Bad: no space around operator

margin: 5px+5px;

Bad: more than one space around operator

margin: 5px   +   5px;

Good

margin: 5px + 5px;

Note that this linter only applies to actual, evaluated operators. So values like nth-child(2n+1), 10px/12px, and my-font will not be linted, as they are valid CSS.

The style option allows you to specify a different preferred style.

Configuration Option	Description
style	one_space, at_least_one_space, no_space (default one_space)

SpaceBeforeBrace

Opening braces should be preceded by a single space.

Bad: no space before brace

p{
  ...
}

Bad: more than one space before brace

p  {
  ...
}

Good

p {
  ...
}

Setting allow_single_line_padding to true allows you to use extra spaces to nicely align single line blocks, so you can write:

.icon-chevron-up    { &:before { content: "\e030"; } }
.icon-chevron-down  { &:before { content: "\e031"; } }
.icon-chevron-left  { &:before { content: "\e032"; } }
.icon-chevron-right { &:before { content: "\e033"; } }

Set style to new_line if you prefer to use a new line before braces, rather than a single space.

p
{
  ...
}

Configuration Option	Description
allow_single_line_padding	Allow single line blocks to have extra spaces for nicer formatting (default false)
style	space or new_line (default space)

SpaceBetweenParens

Parentheses should not be padded with spaces.

Bad

@include box-shadow( 0 2px 2px rgba( 0, 0, 0, .2 ) );
color: rgba( 0, 0, 0, .1 );

Good

@include box-shadow(0 2px 2px rgba(0, 0, 0, .2));
color: rgba(0, 0, 0, .1);

Configuration Option	Description
spaces	Spaces to require between parentheses (default 0)

StringQuotes

String literals should be written with single quotes unless using double quotes would save on escape characters.

Bad: double quotes

content: "hello";

Good: single quotes

content: 'hello';

Good: double quotes prevent the need for escaping single quotes

content: "'hello'";

Single quotes are easier to type by virtue of not requiring the Shift key on most popular keyboard layouts.

Configuration Option	Description
style	single_quotes or double_quotes (default single_quotes)

TrailingSemicolon

Property values; @extend, @include, and @import directives; and variable declarations should always end with a semicolon.

Bad: no semicolon

p {
  color: #fff
}

Bad: space between value and semicolon

p {
  color: #fff ;
}

Good

p {
  color: #fff;
}

CSS allows you to omit the semicolon if the statement is the last statement in the rule set. However, this introduces inconsistency and requires anyone adding a property after that property to remember to append a semicolon.

TrailingWhitespace

Reports lines containing trailing whitespace.

TrailingZero

Disabled by default

Don't write trailing zeros for numeric values with a decimal point.

Bad: unnecessary trailing zero

margin: .500em;

Good: no trailing zero

margin: .5em;

The extra zeros are unnecessary and just add additional bytes to the resulting generated CSS.

TransitionAll

Disabled by default

Don't use the all keyword to specify transition properties.

Bad: use of transition all

transition: all .5s ease-in;

Good: explicitly specify properties to transition

transition: color .5s ease-in, margin-bottom .5s ease-in;

UnnecessaryMantissa

Numeric values should not contain unnecessary fractional portions.

Bad

margin: 1.0em;

Good

margin: 1em;

Sass will automatically convert integers to floats when necessary, making the use of a fractional component in a value to "force" it to be a floating point number unnecessary. For example, the following code:

$margin: 1;
p { margin: $margin / 2; }

...will compile to:

p { margin: 0.5; }

UnnecessaryParentReference

Do not use parent selector references (&) when they would otherwise be unnecessary.

Bad

.foo {
  & > .bar {
    ...
  }
}

Good

.foo {
  > .bar {
  }
}

UrlFormat

URLs should be valid and not contain protocols or domain names.

Including protocols or domains in URLs makes them brittle to change, and also unnecessarily increases the size of your CSS documents, reducing performance.

Bad: protocol and domain present

background: url('https://example.com/assets/image.png');

Good

background: url('assets/image.png');

UrlQuotes

URLs should always be enclosed within quotes.

Bad: no enclosing quotes

background: url(example.png);

Good

background: url('example.png');

Using quoted URLs is consistent with using other Sass asset helpers, which also expect quoted strings. It also works better with most syntax highlighters, and makes it easier to escape characters, as the escape rules for strings apply, rather than the different set of rules for literal URLs.

See the URL type documentation for more information.

VariableForProperty

Disabled by default

Properties, like color and font, are easier to read and maintain when defined using variables rather than literals.

Bad

p {
  color: red;
}

.warning {
  color: #ff0;
}

Good

p {
  color: $body-text;
}

.warning {
  color: $body-warning;
}

By using variables, you can describe the semantics of the property value rather than just using the literal value (improving readability) and also make it easier to perform side-wide changes as you only need to change the value in one place, rather than several.

By default, this linter does not enforce the use of variables for any property. To enable it, set the properties option in your configuration, e.g.

linters:
  VariableForProperty:
    enabled: true
    properties:
      - color
      - font

Note that values like currentColor, inherit, and transparent will not be reported, as they are special kinds of values that convey additional meaning.

Configuration Option	Description
properties	Array of property names to check

VendorPrefix

Avoid vendor prefixes. That is, don't write them yourself.

Instead, you can use Autoprefixer or mixins -- such as Compass or Bourbon -- to add vendor prefixes to your code. (If using your own mixins, make sure to exempt their source from this linter.)

At-rules, selectors, properties, and values are all checked. (See the examples below.)

The default identifier_list, base, should include everything that Autoprefixer addresses. You could also use a list covering Bourbon's CSS3 mixins: bourbon. If neither of those suit you, you can write your own identifier list.

Additionally, you can manually include or exclude identifiers from the identifier list -- if, for example, you want to use pretty much all of the base list but also want to allow yourself to use vendor prefixed transform properties, for one reason or another.

All identifiers used by the identifier_list, additional_identifiers, or excluded_identifiers are stripped of vendor prefixes. See the predefined lists for examples.

Bad: vendor prefixes

@-webkit-keyframes anim {
  0% { opacity: 0; }
}

::-moz-placeholder {
  color: red;
}

.foo {
  -webkit-transition: none;
}

.bar {
  position: -moz-sticky;
}

Good

// With Autoprefixer ...
@keyframes anim {
  0% { opacity: 0; }
}

::placeholder {
  color: red;
}

.foo {
  transition: none;
}

.bar {
  position: sticky;
}

// With Bourbon mixin
@include placeholder {
  color: red;
}

Configuration Option	Description
identifier_list	Name of predefined identifier list to use (base or bourbon) or an array of identifiers (default base)
additional_identifiers	Identifiers to lint, in addition to the identifier_list (default [])
excluded_identifiers	Identifers in the identifier_list and additional_identifiers to exclude from linting (default [])

ZeroUnit

Omit length units on zero values.

Bad: unnecessary units

margin: 0px;

Good

margin: 0;

Zero is zero regardless of the units of length.

Note that this only applies to lengths, since it is invalid to omit units for other types such as angles or times.