Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD025 - Multiple top level headers in the same document

Tags: headers

Aliases: single-h1

Parameters: level (number; default 1)

This rule is triggered when a top level header is in use (the first line of the file is a h1 header), and more than one h1 header is in use in the document:

# Top level header

# Another top level header

To fix, structure your document so that there is a single h1 header that is the title for the document, and all later headers are h2 or lower level headers:

# Title

## Header

## Another header

Rationale: A top level header is a h1 on the first line of the file, and serves as the title for the document. If this convention is in use, then there can not be more than one title for the document, and the entire document should be contained within this header.

Note: The level parameter can be used to change the top level (ex: to h2) in cases where an h1 is added externally.

MD005 - Inconsistent indentation for list items at the same level

Tags: bullet, ul, indentation

Aliases: list-indent

This rule is triggered when list items are parsed as being at the same level, but don't have the same indentation:

* Item 1
    * Nested Item 1
    * Nested Item 2
   * A misaligned item

Usually this rule will be triggered because of a typo. Correct the indentation for the list to fix it:

* Item 1
  * Nested Item 1
  * Nested Item 2
  * Nested Item 3

This cop checks for unneeded usages of splat expansion

Example:

# bad

a = *[1, 2, 3]
a = *'a'
a = *1

begin
  foo
rescue *[StandardError, ApplicationError]
  bar
end

case foo
when *[1, 2, 3]
  bar
else
  baz
end

Example:

# good

c = [1, 2, 3]
a = *c
a, b = *c
a, *b = *c
a = *1..10
a = ['a']

begin
  foo
rescue StandardError, ApplicationError
  bar
end

case foo
when *[1, 2, 3]
  bar
else
  baz
end

This cop makes sure that accessor methods are named properly.

Example:

# bad
def set_attribute(value)
end

# good
def attribute=(value)
end

# bad
def get_attribute
end

# good
def attribute
end

MD025 - Multiple top level headers in the same document

Tags: headers

Aliases: single-h1

Parameters: level (number; default 1)

This rule is triggered when a top level header is in use (the first line of the file is a h1 header), and more than one h1 header is in use in the document:

# Top level header

# Another top level header

To fix, structure your document so that there is a single h1 header that is the title for the document, and all later headers are h2 or lower level headers:

# Title

## Header

## Another header

Rationale: A top level header is a h1 on the first line of the file, and serves as the title for the document. If this convention is in use, then there can not be more than one title for the document, and the entire document should be contained within this header.

Note: The level parameter can be used to change the top level (ex: to h2) in cases where an h1 is added externally.

MD007 - Unordered list indentation

Tags: bullet, ul, indentation

Aliases: ul-indent

Parameters: indent (number; default 2)

This rule is triggered when list items are not indented by the configured number of spaces (default: 2).

Example:

* List item
   * Nested list item indented by 3 spaces

Corrected Example:

* List item
  * Nested list item indented by 2 spaces

Rationale (2 space indent): indenting by 2 spaces allows the content of a nested list to be in line with the start of the content of the parent list when a single space is used after the list marker.

Rationale (4 space indent): Same indent as code blocks, simpler for editors to implement. See http://www.cirosantilli.com/markdown-styleguide/#indented-lists for more information.

In addition, this is a compatibility issue with multi-markdown parsers, which require a 4 space indents. See http://support.markedapp.com/discussions/problems/21-sub-lists-not-indenting for a description of the problem.

This cop checks for rescue blocks with no body.

Example:

# bad

def some_method
  do_something
rescue
  # do nothing
end

Example:

# bad

begin
  do_something
rescue
  # do nothing
end

Example:

# good

def some_method
  do_something
rescue
  handle_exception
end

Example:

# good

begin
  do_something
rescue
  handle_exception
end

MD034 - Bare URL used

Tags: links, url

Aliases: no-bare-urls

This rule is triggered whenever a URL is given that isn't surrounded by angle brackets:

For more information, see http://www.example.com/.

To fix this, add angle brackets around the URL:

For more information, see <http:></http:>.

Rationale: Without angle brackets, the URL isn't converted into a link in many markdown parsers.

Note: if you do want a bare URL without it being converted into a link, enclose it in a code block, otherwise in some markdown parsers it will be converted:

`http://www.example.com`

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.