Rules

When linting a document with yamllint, a series of rules (such as line-length, trailing-spaces, etc.) are checked against.

A configuration file can be used to enable or disable these rules, to set their level (error or warning), but also to tweak their options.

This page describes the rules and their options.

braces

Use this rule to control the number of spaces inside braces ({ and }).

Options

  • min-spaces-inside defines the minimal number of spaces required inside braces.
  • max-spaces-inside defines the maximal number of spaces allowed inside braces.
  • min-spaces-inside-empty defines the minimal number of spaces required inside empty braces.
  • max-spaces-inside-empty defines the maximal number of spaces allowed inside empty braces.

Examples

  1. With braces: {min-spaces-inside: 0, max-spaces-inside: 0}

    the following code snippet would PASS:

    object: {key1: 4, key2: 8}
    

    the following code snippet would FAIL:

    object: { key1: 4, key2: 8 }
    
  2. With braces: {min-spaces-inside: 1, max-spaces-inside: 3}

    the following code snippet would PASS:

    object: { key1: 4, key2: 8 }
    

    the following code snippet would PASS:

    object: { key1: 4, key2: 8   }
    

    the following code snippet would FAIL:

    object: {    key1: 4, key2: 8   }
    

    the following code snippet would FAIL:

    object: {key1: 4, key2: 8 }
    
  3. With braces: {min-spaces-inside-empty: 0, max-spaces-inside-empty: 0}

    the following code snippet would PASS:

    object: {}
    

    the following code snippet would FAIL:

    object: { }
    
  4. With braces: {min-spaces-inside-empty: 1, max-spaces-inside-empty: -1}

    the following code snippet would PASS:

    object: {         }
    

    the following code snippet would FAIL:

    object: {}
    

brackets

Use this rule to control the number of spaces inside brackets ([ and ]).

Options

  • min-spaces-inside defines the minimal number of spaces required inside brackets.
  • max-spaces-inside defines the maximal number of spaces allowed inside brackets.
  • min-spaces-inside-empty defines the minimal number of spaces required inside empty brackets.
  • max-spaces-inside-empty defines the maximal number of spaces allowed inside empty brackets.

Examples

  1. With brackets: {min-spaces-inside: 0, max-spaces-inside: 0}

    the following code snippet would PASS:

    object: [1, 2, abc]
    

    the following code snippet would FAIL:

    object: [ 1, 2, abc ]
    
  2. With brackets: {min-spaces-inside: 1, max-spaces-inside: 3}

    the following code snippet would PASS:

    object: [ 1, 2, abc ]
    

    the following code snippet would PASS:

    object: [ 1, 2, abc   ]
    

    the following code snippet would FAIL:

    object: [    1, 2, abc   ]
    

    the following code snippet would FAIL:

    object: [1, 2, abc ]
    
  3. With brackets: {min-spaces-inside-empty: 0, max-spaces-inside-empty: 0}

    the following code snippet would PASS:

    object: []
    

    the following code snippet would FAIL:

    object: [ ]
    
  4. With brackets: {min-spaces-inside-empty: 1, max-spaces-inside-empty: -1}

    the following code snippet would PASS:

    object: [         ]
    

    the following code snippet would FAIL:

    object: []
    

colons

Use this rule to control the number of spaces before and after colons (:).

Options

  • max-spaces-before defines the maximal number of spaces allowed before colons (use -1 to disable).
  • max-spaces-after defines the maximal number of spaces allowed after colons (use -1 to disable).

Examples

  1. With colons: {max-spaces-before: 0, max-spaces-after: 1}

    the following code snippet would PASS:

    object:
      - a
      - b
    key: value
    
  2. With colons: {max-spaces-before: 1}

    the following code snippet would PASS:

    object :
      - a
      - b
    

    the following code snippet would FAIL:

    object  :
      - a
      - b
    
  3. With colons: {max-spaces-after: 2}

    the following code snippet would PASS:

    first:  1
    second: 2
    third:  3
    

    the following code snippet would FAIL:

    first: 1
    2nd:   2
    third: 3
    

commas

Use this rule to control the number of spaces before and after commas (,).

Options

  • max-spaces-before defines the maximal number of spaces allowed before commas (use -1 to disable).
  • min-spaces-after defines the minimal number of spaces required after commas.
  • max-spaces-after defines the maximal number of spaces allowed after commas (use -1 to disable).

Examples

  1. With commas: {max-spaces-before: 0}

    the following code snippet would PASS:

    strange var:
      [10, 20, 30, {x: 1, y: 2}]
    

    the following code snippet would FAIL:

    strange var:
      [10, 20 , 30, {x: 1, y: 2}]
    
  2. With commas: {max-spaces-before: 2}

    the following code snippet would PASS:

    strange var:
      [10  , 20 , 30,  {x: 1  , y: 2}]
    
  3. With commas: {max-spaces-before: -1}

    the following code snippet would PASS:

    strange var:
      [10,
       20   , 30
       ,   {x: 1, y: 2}]
    
  4. With commas: {min-spaces-after: 1, max-spaces-after: 1}

    the following code snippet would PASS:

    strange var:
      [10, 20,30, {x: 1, y: 2}]
    

    the following code snippet would FAIL:

    strange var:
      [10, 20,30,   {x: 1,   y: 2}]
    
  5. With commas: {min-spaces-after: 1, max-spaces-after: 3}

    the following code snippet would PASS:

    strange var:
      [10, 20,  30,  {x: 1,   y: 2}]
    
  6. With commas: {min-spaces-after: 0, max-spaces-after: 1}

    the following code snippet would PASS:

    strange var:
      [10, 20,30, {x: 1, y: 2}]
    

comments

Use this rule to control the position and formatting of comments.

Options

  • Use require-starting-space to require a space character right after the #. Set to true to enable, false to disable.
  • min-spaces-from-content is used to visually separate inline comments from content. It defines the minimal required number of spaces between a comment and its preceding content.

Examples

  1. With comments: {require-starting-space: true}

    the following code snippet would PASS:

    # This sentence
    # is a block comment
    

    the following code snippet would PASS:

    ##############################
    ## This is some documentation
    

    the following code snippet would FAIL:

    #This sentence
    #is a block comment
    
  2. With comments: {min-spaces-from-content: 2}

    the following code snippet would PASS:

    x = 2 ^ 127 - 1  # Mersenne prime number
    

    the following code snippet would FAIL:

    x = 2 ^ 127 - 1 # Mersenne prime number
    

comments-indentation

Use this rule to force comments to be indented like content.

Examples

  1. With comments-indentation: {}

    the following code snippet would PASS:

    # Fibonacci
    [0, 1, 1, 2, 3, 5]
    

    the following code snippet would FAIL:

      # Fibonacci
    [0, 1, 1, 2, 3, 5]
    

    the following code snippet would PASS:

    list:
        - 2
        - 3
        # - 4
        - 5
    

    the following code snippet would FAIL:

    list:
        - 2
        - 3
    #    - 4
        - 5
    

    the following code snippet would PASS:

    # This is the first object
    obj1:
      - item A
      # - item B
    # This is the second object
    obj2: []
    

    the following code snippet would PASS:

    # This sentence
    # is a block comment
    

    the following code snippet would FAIL:

    # This sentence
     # is a block comment
    

document-end

Use this rule to require or forbid the use of document end marker (...).

Options

  • Set present to true when the document end marker is required, or to false when it is forbidden.

Examples

  1. With document-end: {present: true}

    the following code snippet would PASS:

    ---
    this:
      is: [a, document]
    ...
    ---
    - this
    - is: another one
    ...
    

    the following code snippet would FAIL:

    ---
    this:
      is: [a, document]
    ---
    - this
    - is: another one
    ...
    
  2. With document-end: {present: false}

    the following code snippet would PASS:

    ---
    this:
      is: [a, document]
    ---
    - this
    - is: another one
    

    the following code snippet would FAIL:

    ---
    this:
      is: [a, document]
    ...
    ---
    - this
    - is: another one
    

document-start

Use this rule to require or forbid the use of document start marker (---).

Options

  • Set present to true when the document start marker is required, or to false when it is forbidden.

Examples

  1. With document-start: {present: true}

    the following code snippet would PASS:

    ---
    this:
      is: [a, document]
    ---
    - this
    - is: another one
    

    the following code snippet would FAIL:

    this:
      is: [a, document]
    ---
    - this
    - is: another one
    
  2. With document-start: {present: false}

    the following code snippet would PASS:

    this:
      is: [a, document]
    ...
    

    the following code snippet would FAIL:

    ---
    this:
      is: [a, document]
    ...
    

empty-lines

Use this rule to set a maximal number of allowed consecutive blank lines.

Options

  • max defines the maximal number of empty lines allowed in the document.
  • max-start defines the maximal number of empty lines allowed at the beginning of the file. This option takes precedence over max.
  • max-end defines the maximal number of empty lines allowed at the end of the file. This option takes precedence over max.

Examples

  1. With empty-lines: {max: 1}

    the following code snippet would PASS:

    - foo:
        - 1
        - 2
    
    - bar: [3, 4]
    

    the following code snippet would FAIL:

    - foo:
        - 1
        - 2
    
    
    - bar: [3, 4]
    

hyphens

Use this rule to control the number of spaces after hyphens (-).

Options

  • max-spaces-after defines the maximal number of spaces allowed after hyphens.

Examples

  1. With hyphens: {max-spaces-after: 1}

    the following code snippet would PASS:

    - first list:
        - a
        - b
    - - 1
      - 2
      - 3
    

    the following code snippet would FAIL:

    -  first list:
         - a
         - b
    

    the following code snippet would FAIL:

    - - 1
      -  2
      - 3
    
  2. With hyphens: {max-spaces-after: 3}

    the following code snippet would PASS:

    -   key
    -  key2
    - key42
    

    the following code snippet would FAIL:

    -    key
    -   key2
    -  key42
    

indentation

Use this rule to control the indentation.

Options

  • spaces defines the indentation width, in spaces. Set either to an integer (e.g. 2 or 4, representing the number of spaces in an indentation level) or to consistent to allow any number, as long as it remains the same within the file.
  • indent-sequences defines whether block sequences should be indented or not (when in a mapping, this indentation is not mandatory – some people perceive the - as part of the indentation). Possible values: true, false, whatever and consistent. consistent requires either all block sequences to be indented, or none to be. whatever means either indenting or not indenting individual block sequences is OK.
  • check-multi-line-strings defines whether to lint indentation in multi-line strings. Set to true to enable, false to disable.

Examples

  1. With indentation: {spaces: 1}

    the following code snippet would PASS:

    history:
     - name: Unix
       date: 1969
     - name: Linux
       date: 1991
    nest:
     recurse:
      - haystack:
         needle
    
  2. With indentation: {spaces: 4}

    the following code snippet would PASS:

    history:
        - name: Unix
          date: 1969
        - name: Linux
          date: 1991
    nest:
        recurse:
            - haystack:
                  needle
    

    the following code snippet would FAIL:

    history:
      - name: Unix
        date: 1969
      - name: Linux
        date: 1991
    nest:
      recurse:
        - haystack:
            needle
    
  3. With indentation: {spaces: consistent}

    the following code snippet would PASS:

    history:
       - name: Unix
         date: 1969
       - name: Linux
         date: 1991
    nest:
       recurse:
          - haystack:
               needle
    

    the following code snippet would FAIL:

    some:
      Russian:
          dolls
    
  4. With indentation: {spaces: 2, indent-sequences: false}

    the following code snippet would PASS:

    list:
    - flying
    - spaghetti
    - monster
    

    the following code snippet would FAIL:

    list:
      - flying
      - spaghetti
      - monster
    
  5. With indentation: {spaces: 2, indent-sequences: whatever}

    the following code snippet would PASS:

    list:
    - flying:
      - spaghetti
      - monster
    - not flying:
        - spaghetti
        - sauce
    
  6. With indentation: {spaces: 2, indent-sequences: consistent}

    the following code snippet would PASS:

    - flying:
      - spaghetti
      - monster
    - not flying:
      - spaghetti
      - sauce
    

    the following code snippet would FAIL:

    - flying:
        - spaghetti
        - monster
    - not flying:
      - spaghetti
      - sauce
    
  7. With indentation: {spaces: 4, check-multi-line-strings: true}

    the following code snippet would PASS:

    Blaise Pascal:
        Je vous écris une longue lettre parce que
        je n'ai pas le temps d'en écrire une courte.
    

    the following code snippet would PASS:

    Blaise Pascal: Je vous écris une longue lettre parce que
                   je n'ai pas le temps d'en écrire une courte.
    

    the following code snippet would FAIL:

    Blaise Pascal: Je vous écris une longue lettre parce que
      je n'ai pas le temps d'en écrire une courte.
    

    the following code snippet would FAIL:

    C code:
        void main() {
            printf("foo");
        }
    

    the following code snippet would PASS:

    C code:
        void main() {
        printf("bar");
        }
    

key-duplicates

Use this rule to prevent multiple entries with the same key in mappings.

Examples

  1. With key-duplicates: {}

    the following code snippet would PASS:

    - key 1: v
      key 2: val
      key 3: value
    - {a: 1, b: 2, c: 3}
    

    the following code snippet would FAIL:

    - key 1: v
      key 2: val
      key 1: value
    

    the following code snippet would FAIL:

    - {a: 1, b: 2, b: 3}
    

    the following code snippet would FAIL:

    duplicated key: 1
    "duplicated key": 2
    
    other duplication: 1
    ? >-
        other
        duplication
    : 2
    

line-length

Use this rule to set a limit to lines length.

Options

  • max defines the maximal (inclusive) length of lines.
  • allow-non-breakable-words is used to allow non breakable words (without spaces inside) to overflow the limit. This is useful for long URLs, for instance. Use true to allow, false to forbid.
  • allow-non-breakable-inline-mappings implies allow-non-breakable-words and extends it to also allow non-breakable words in inline mappings.

Examples

  1. With line-length: {max: 70}

    the following code snippet would PASS:

    long sentence:
      Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do
      eiusmod tempor incididunt ut labore et dolore magna aliqua.
    

    the following code snippet would FAIL:

    long sentence:
      Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
      tempor incididunt ut labore et dolore magna aliqua.
    
  2. With line-length: {max: 60, allow-non-breakable-words: true}

    the following code snippet would PASS:

    this:
      is:
        - a:
            http://localhost/very/very/very/very/very/very/very/very/long/url
    
    # this comment is too long,
    # but hard to split:
    # http://localhost/another/very/very/very/very/very/very/very/very/long/url
    

    the following code snippet would FAIL:

    - this line is waaaaaaaaaaaaaay too long but could be easily split...
    

    and the following code snippet would also FAIL:

    - foobar: http://localhost/very/very/very/very/very/very/very/very/long/url
    
  3. With line-length: {max: 60, allow-non-breakable-words: true, allow-non-breakable-inline-mappings: true}

    the following code snippet would PASS:

    - foobar: http://localhost/very/very/very/very/very/very/very/very/long/url
    
  4. With line-length: {max: 60, allow-non-breakable-words: false}

    the following code snippet would FAIL:

    this:
      is:
        - a:
            http://localhost/very/very/very/very/very/very/very/very/long/url
    

new-line-at-end-of-file

Use this rule to require a new line character (\n) at the end of files.

The POSIX standard requires the last line to end with a new line character. All UNIX tools expect a new line at the end of files. Most text editors use this convention too.

new-lines

Use this rule to force the type of new line characters.

Options

  • Set type to unix to use UNIX-typed new line characters (\n), or dos to use DOS-typed new line characters (\r\n).

trailing-spaces

Use this rule to forbid trailing spaces at the end of lines.

Examples

  1. With trailing-spaces: {}

    the following code snippet would PASS:

    this document doesn't contain
    any trailing
    spaces
    

    the following code snippet would FAIL:

    this document contains     
    trailing spaces
    on lines 1 and 3         
    

truthy

Use this rule to forbid truthy values that are not quoted nor explicitly typed.

This would prevent YAML parsers from transforming [yes, FALSE, Off] into [true, false, false] or {y: 1, yes: 2, on: 3, true: 4, True: 5} into {y: 1, true: 5}.

Examples

  1. With truthy: {}

    the following code snippet would PASS:

    boolean: true
    
    object: {"True": 1, 1: "True"}
    
    "yes":  1
    "on":   2
    "true": 3
    "True": 4
    
     explicit:
       string1: !!str True
       string2: !!str yes
       string3: !!str off
       encoded: !!binary |
                  True
                  OFF
                  pad==  # this decodes as 'N»ž8Qii'
       boolean1: !!bool true
       boolean2: !!bool "false"
       boolean3: !!bool FALSE
       boolean4: !!bool True
       boolean5: !!bool off
       boolean6: !!bool NO
    

    the following code snippet would FAIL:

    object: {True: 1, 1: True}
    

    the following code snippet would FAIL:

    yes:  1
    on:   2
    true: 3
    True: 4