yamllint - Man Page

On Fedora / CentOS (note: EPEL is required on CentOS):

sudo dnf install yamllint

On Debian 8+ / Ubuntu 16.04+:

sudo apt-get install yamllint

On Mac OS 10.11+:

brew install yamllint

On FreeBSD:

pkg install py36-yamllint

On OpenBSD:

doas pkg_add py3-yamllint

Alternatively using pip, the Python package manager:

pip install --user yamllint

If you prefer installing from source, you can run, from the source directory:

python -m build
pip install --user dist/yamllint-*.tar.gz

Basic usage:

yamllint file.yml other-file.yaml

You can also lint all YAML files in a whole directory:

yamllint .

Or lint a YAML stream from standard input:

echo -e 'this: is\nvalid: YAML' | yamllint -

The output will look like (colors are not displayed here):

file.yml
  1:4       error    trailing spaces  (trailing-spaces)
  4:4       error    wrong indentation: expected 4 but found 3  (indentation)
  5:4       error    duplication of key "id-00042" in mapping  (key-duplicates)
  6:6       warning  comment not indented like content  (comments-indentation)
  12:6      error    too many spaces after hyphen  (hyphens)
  15:12     error    too many spaces before comma  (commas)

other-file.yaml
  1:1       warning  missing document start "---"  (document-start)
  6:81      error    line too long (87 > 80 characters)  (line-length)
  10:1      error    too many blank lines (4 > 2)  (empty-lines)
  11:4      error    too many spaces inside braces  (braces)

By default, the output of yamllint is colored when run from a terminal, and pure text in other cases. Add the -f standard arguments to force non-colored output. Use the -f colored arguments to force colored output.

Add the -f parsable arguments if you need an output format parsable by a machine (for instance for syntax highlighting in text editors). The output will then look like:

file.yml:6:2: [warning] missing starting space in comment (comments)
file.yml:57:1: [error] trailing spaces (trailing-spaces)
file.yml:60:3: [error] wrong indentation: expected 4 but found 2 (indentation)

If you have a custom linting configuration file (see how to configure yamllint), it can be passed to yamllint using the -c option:

yamllint -c ~/myconfig file.yaml

NOTE:

If you have a .yamllint file in your working directory, it will be automatically loaded as configuration by yamllint.

yamllint uses a set of rules to check source files for problems. Each rule is independent from the others, and can be enabled, disabled or tweaked. All these settings can be gathered in a configuration file.

To use a custom configuration file, use the -c option:

yamllint -c /path/to/myconfig file-to-lint.yaml

If -c is not provided, yamllint will look for a configuration file in the following locations (by order of preference):

• a file named .yamllint, .yamllint.yaml, or .yamllint.yml in the current working directory, or a parent directory (the search for this file is terminated at the user's home or filesystem root)
• a filename referenced by $YAMLLINT_CONFIG_FILE, if set
• a file named $XDG_CONFIG_HOME/yamllint/config or ~/.config/yamllint/config, if present

Finally if no config file is found, the default configuration is applied.

Unless told otherwise, yamllint uses its default configuration:

---

yaml-files:
  - '*.yaml'
  - '*.yml'
  - '.yamllint'

rules:
  anchors: enable
  braces: enable
  brackets: enable
  colons: enable
  commas: enable
  comments:
    level: warning
  comments-indentation:
    level: warning
  document-end: disable
  document-start:
    level: warning
  empty-lines: enable
  empty-values: disable
  float-values: disable
  hyphens: enable
  indentation: enable
  key-duplicates: enable
  key-ordering: disable
  line-length: enable
  new-line-at-end-of-file: enable
  new-lines: enable
  octal-values: disable
  quoted-strings: disable
  trailing-spaces: enable
  truthy:
    level: warning

Details on rules can be found on the rules page.

There is another pre-defined configuration named relaxed. As its name suggests, it is more tolerant:

---

extends: default

rules:
  braces:
    level: warning
    max-spaces-inside: 1
  brackets:
    level: warning
    max-spaces-inside: 1
  colons:
    level: warning
  commas:
    level: warning
  comments: disable
  comments-indentation: disable
  document-start: disable
  empty-lines:
    level: warning
  hyphens:
    level: warning
  indentation:
    level: warning
    indent-sequences: consistent
  line-length:
    level: warning
    allow-non-breakable-inline-mappings: true
  truthy: disable

It can be chosen using:

yamllint -d relaxed file.yml

When writing a custom configuration file, you don't need to redefine every rule. Just extend the default configuration (or any already-existing configuration file).

For instance, if you just want to disable the comments-indentation rule, your file could look like this:

# This is my first, very own configuration file for yamllint!
# It extends the default conf by adjusting some options.

extends: default

rules:
  comments-indentation: disable  # don't bother me with this rule

Similarly, if you want to set the line-length rule as a warning and be less strict on block sequences indentation:

extends: default

rules:
  # 80 chars should be enough, but don't fail if a line is longer
  line-length:
    max: 80
    level: warning

  # accept both     key:
  #                   - item
  #
  # and             key:
  #                 - item
  indentation:
    indent-sequences: whatever

It is possible -- although not recommended -- to pass custom configuration options to yamllint with the -d (short for --config-data) option.

Its content can either be the name of a pre-defined conf (example: default or relaxed) or a serialized YAML object describing the configuration.

For instance:

yamllint -d "{extends: relaxed, rules: {line-length: {max: 120}}}" file.yaml

Problems detected by yamllint can be raised either as errors or as warnings. The CLI will output them (with different colors when using the colored output format, or auto when run from a terminal).

By default the script will exit with a return code 1 only when there is one or more error(s).

However if strict mode is enabled with the -s (or --strict) option, the return code will be:

• 0 if no errors or warnings occur
• 1 if one or more errors occur
• 2 if no errors occur, but one or more warnings occur

If the script is invoked with the --no-warnings option, it won't output warning level problems, only error level ones.

To configure what yamllint should consider as YAML files when listing directories, set yaml-files configuration option. The default is:

yaml-files:
  - '*.yaml'
  - '*.yml'
  - '.yamllint'

The same rules as for ignoring paths apply (.gitignore-style path pattern, see below).

If you need to know the exact list of files that yamllint would process, without really linting them, you can use --list-files:

yamllint --list-files .

It is possible to exclude specific files or directories, so that the linter doesn't process them. They can be provided either as a list of paths, or as a bulk string.

You can either totally ignore files (they won't be looked at):

extends: default

ignore: |
  /this/specific/file.yaml
  all/this/directory/
  *.template.yaml

# or:

ignore:
  - /this/specific/file.yaml
  - all/this/directory/
  - '*.template.yaml'

or ignore paths only for specific rules:

extends: default

rules:
  trailing-spaces:
    ignore: |
      /this-file-has-trailing-spaces-but-it-is-OK.yaml
      /generated/*.yaml

# or:

rules:
  trailing-spaces:
    ignore:
      - /this-file-has-trailing-spaces-but-it-is-OK.yaml
      - /generated/*.yaml

Note that this .gitignore-style path pattern allows complex path exclusion/inclusion, see the pathspec README file for more details. Here is a more complex example:

# For all rules
ignore: |
  *.dont-lint-me.yaml
  /bin/
  !/bin/*.lint-me-anyway.yaml

extends: default

rules:
  key-duplicates:
    ignore: |
      generated
      *.template.yaml
  trailing-spaces:
    ignore: |
      *.ignore-trailing-spaces.yaml
      ascii-art/*

You can also use the .gitignore file (or any list of files) through:

ignore-from-file: .gitignore

or:

ignore-from-file: [.gitignore, .yamlignore]

NOTE:

However, this is mutually exclusive with the ignore key.

If you need to know the exact list of files that yamllint would process, without really linting them, you can use --list-files:

yamllint --list-files .

It is possible to set the locale option globally. This is passed to Python's locale.setlocale, so an empty string "" will use the system default locale, while e.g. "en_US.UTF-8" will use that.

Currently this only affects the key-ordering rule. The default will order by Unicode code point number, while locales will sort case and accents properly as well.

extends: default

locale: en_US.UTF-8

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.

• anchors
• braces
• brackets
• colons
• commas
• comments
• comments-indentation
• document-end
• document-start
• empty-lines
• empty-values
• float-values
• hyphens
• indentation
• key-duplicates
• key-ordering
• line-length
• new-line-at-end-of-file
• new-lines
• octal-values
• quoted-strings
• trailing-spaces
• truthy

Use this rule to report duplicated anchors and aliases referencing undeclared anchors.

Options

• Set forbid-undeclared-aliases to true to avoid aliases that reference an anchor that hasn't been declared (either not declared at all, or declared later in the document).
• Set forbid-duplicated-anchors to true to avoid duplications of a same anchor.
• Set forbid-unused-anchors to true to avoid anchors being declared but not used anywhere in the YAML document via alias.

Default values (when enabled)

rules:
  anchors:
    forbid-undeclared-aliases: true
    forbid-duplicated-anchors: false
    forbid-unused-anchors: false

Examples

1. With anchors: {forbid-undeclared-aliases: true}

   the following code snippet would PASS:

   ---
   - &anchor
     foo: bar
   - *anchor

   the following code snippet would FAIL:

   ---
   - &anchor
     foo: bar
   - *unknown

   the following code snippet would FAIL:

   ---
   - &anchor
     foo: bar
   - <<: *unknown
     extra: value

2. With anchors: {forbid-duplicated-anchors: true}

   the following code snippet would PASS:

   ---
   - &anchor1 Foo Bar
   - &anchor2 [item 1, item 2]

   the following code snippet would FAIL:

   ---
   - &anchor Foo Bar
   - &anchor [item 1, item 2]

3. With anchors: {forbid-unused-anchors: true}

   the following code snippet would PASS:

   ---
   - &anchor
     foo: bar
   - *anchor

   the following code snippet would FAIL:

   ---
   - &anchor
     foo: bar
   - items:
     - item1
     - item2

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

Options

• forbid is used to forbid the use of flow mappings which are denoted by surrounding braces ({ and }). Use true to forbid the use of flow mappings completely. Use non-empty to forbid the use of all flow mappings except for empty ones.
• 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.

Default values (when enabled)

rules:
  braces:
    forbid: false
    min-spaces-inside: 0
    max-spaces-inside: 0
    min-spaces-inside-empty: -1
    max-spaces-inside-empty: -1

Examples

1. With braces: {forbid: true}

   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: {forbid: non-empty}

   the following code snippet would PASS:

   object: {}

   the following code snippet would FAIL:

   object: { key1: 4, key2: 8 }

3. 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 }

4. 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 }

5. 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: { }

6. 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: {}

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

Options

• forbid is used to forbid the use of flow sequences which are denoted by surrounding brackets ([ and ]). Use true to forbid the use of flow sequences completely. Use non-empty to forbid the use of all flow sequences except for empty ones.
• 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.

Default values (when enabled)

rules:
  brackets:
    forbid: false
    min-spaces-inside: 0
    max-spaces-inside: 0
    min-spaces-inside-empty: -1
    max-spaces-inside-empty: -1

Examples

1. With brackets: {forbid: true}

   the following code snippet would PASS:

   object:
     - 1
     - 2
     - abc

   the following code snippet would FAIL:

   object: [ 1, 2, abc ]

2. With brackets: {forbid: non-empty}

   the following code snippet would PASS:

   object: []

   the following code snippet would FAIL:

   object: [ 1, 2, abc ]

3. 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 ]

4. 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 ]

5. 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: [ ]

6. 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: []

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).

Default values (when enabled)

rules:
  colons:
    max-spaces-before: 0
    max-spaces-after: 1

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

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).

Default values (when enabled)

rules:
  commas:
    max-spaces-before: 0
    min-spaces-after: 1
    max-spaces-after: 1

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}]

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.
• Use ignore-shebangs to ignore a shebang at the beginning of the file when require-starting-space is set.
• 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.

Default values (when enabled)

rules:
  comments:
    require-starting-space: true
    ignore-shebangs: true
    min-spaces-from-content: 2

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

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

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.

Default values (when enabled)

rules:
  document-end:
    present: true

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

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.

Default values (when enabled)

rules:
  document-start:
    present: true

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]
   ...

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.

Default values (when enabled)

rules:
  empty-lines:
    max: 2
    max-start: 0
    max-end: 0

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]

Use this rule to prevent nodes with empty content, that implicitly result in null values.

Options

• Use forbid-in-block-mappings to prevent empty values in block mappings.
• Use forbid-in-flow-mappings to prevent empty values in flow mappings.
• Use forbid-in-block-sequences to prevent empty values in block sequences.

Default values (when enabled)

rules:
  empty-values:
    forbid-in-block-mappings: true
    forbid-in-flow-mappings: true
    forbid-in-block-sequences: true

Examples

1. With empty-values: {forbid-in-block-mappings: true}

   the following code snippets would PASS:

   some-mapping:
     sub-element: correctly indented

   explicitly-null: null

   the following code snippets would FAIL:

   some-mapping:
   sub-element: incorrectly indented

   implicitly-null:

2. With empty-values: {forbid-in-flow-mappings: true}

   the following code snippet would PASS:

   {prop: null}
   {a: 1, b: 2, c: 3}

   the following code snippets would FAIL:

   {prop: }

   {a: 1, b:, c: 3}

3. With empty-values: {forbid-in-block-sequences: true}

   the following code snippet would PASS:

   some-sequence:
     - string item

   some-sequence:
     - null

   the following code snippets would FAIL:

   some-sequence:
     -

   some-sequence:
     - string item
     -

Use this rule to limit the permitted values for floating-point numbers. YAML permits three classes of float expressions: approximation to real numbers, positive and negative infinity and "not a number".

Options

• Use require-numeral-before-decimal to require floats to start with a numeral (ex 0.0 instead of .0).
• Use forbid-scientific-notation to forbid scientific notation.
• Use forbid-nan to forbid NaN (not a number) values.
• Use forbid-inf to forbid infinite values.

Default values (when enabled)

rules:
  float-values:
    forbid-inf: false
    forbid-nan: false
    forbid-scientific-notation: false
    require-numeral-before-decimal: false

Examples

1. With float-values: {require-numeral-before-decimal: true}

   the following code snippets would PASS:

   anemometer:
     angle: 0.0

   the following code snippets would FAIL:

   anemometer:
     angle: .0

2. With float-values: {forbid-scientific-notation: true}

   the following code snippets would PASS:

   anemometer:
     angle: 0.00001

   the following code snippets would FAIL:

   anemometer:
     angle: 10e-6

3. With float-values: {forbid-nan: true}

   the following code snippets would FAIL:

   anemometer:
     angle: .NaN

   1.

   With float-values: {forbid-inf: true}

   the following code snippets would FAIL:

   anemometer:
     angle: .inf

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

Options

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

Default values (when enabled)

rules:
  hyphens:
    max-spaces-after: 1

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

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.

Default values (when enabled)

rules:
  indentation:
    spaces: consistent
    indent-sequences: true
    check-multi-line-strings: false

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");
       }

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

Options

• Use forbid-duplicated-merge-keys to forbid the usage of multiple merge keys <<.

Default values (when enabled)

rules:
  key-duplicates:
    forbid-duplicated-merge-keys: false

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

2. With key-duplicates: {forbid-duplicated-merge-keys: true}``

   the following code snippet would PASS:

   anchor_one: &anchor_one
     one: one
   anchor_two: &anchor_two
     two: two
   anchor_reference:
     <<: [*anchor_one, *anchor_two]

   the following code snippet would FAIL:

   anchor_one: &anchor_one
     one: one
   anchor_two: &anchor_two
     two: two
   anchor_reference:
     <<: *anchor_one
     <<: *anchor_two

Use this rule to enforce alphabetical ordering of keys in mappings. The sorting order uses the Unicode code point number as a default. As a result, the ordering is case-sensitive and not accent-friendly (see examples below). This can be changed by setting the global locale option.  This allows one to sort case and accents properly.

Examples

1. With key-ordering: {}

   the following code snippet would PASS:

   - key 1: v
     key 2: val
     key 3: value
   - {a: 1, b: 2, c: 3}
   - T-shirt: 1
     T-shirts: 2
     t-shirt: 3
     t-shirts: 4
   - hair: true
     hais: true
     haïr: true
     haïssable: true

   the following code snippet would FAIL:

   - key 2: v
     key 1: val

   the following code snippet would FAIL:

   - {b: 1, a: 2}

   the following code snippet would FAIL:

   - T-shirt: 1
     t-shirt: 2
     T-shirts: 3
     t-shirts: 4

   the following code snippet would FAIL:

   - haïr: true
     hais: true

2. With global option locale: "en_US.UTF-8" and rule key-ordering: {}

   as opposed to before, the following code snippet would now PASS:

   - t-shirt: 1
     T-shirt: 2
     t-shirts: 3
     T-shirts: 4
   - hair: true
     haïr: true
     hais: true
     haïssable: true

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.

Default values (when enabled)

rules:
  line-length:
    max: 80
    allow-non-breakable-words: true
    allow-non-breakable-inline-mappings: false

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

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.

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

Options

• Set type to unix to enforce UNIX-typed new line characters (\n), set type to dos to enforce DOS-typed new line characters (\r\n), or set type to platform to infer the type from the system running yamllint (\n on POSIX / UNIX / Linux / Mac OS systems or \r\n on DOS / Windows systems).

Default values (when enabled)

rules:
  new-lines:
    type: unix

Use this rule to prevent values with octal numbers. In YAML, numbers that start with 0 are interpreted as octal, but this is not always wanted. For instance 010 is the city code of Beijing, and should not be converted to 8.

Options

• Use forbid-implicit-octal to prevent numbers starting with 0.
• Use forbid-explicit-octal to prevent numbers starting with 0o.

Default values (when enabled)

rules:
  octal-values:
    forbid-implicit-octal: true
    forbid-explicit-octal: true

Examples

1. With octal-values: {forbid-implicit-octal: true}

   the following code snippets would PASS:

   user:
     city-code: '010'

   the following code snippets would PASS:

   user:
     city-code: 010,021

   the following code snippets would FAIL:

   user:
     city-code: 010

2. With octal-values: {forbid-explicit-octal: true}

   the following code snippets would PASS:

   user:
     city-code: '0o10'

   the following code snippets would FAIL:

   user:
     city-code: 0o10

Use this rule to forbid any string values that are not quoted, or to prevent quoted strings without needing it. You can also enforce the type of the quote used.

Options

• quote-type defines allowed quotes: single, double or any (default).
• required defines whether using quotes in string values is required (true, default) or not (false), or only allowed when really needed (only-when-needed).
• extra-required is a list of PCRE regexes to force string values to be quoted, if they match any regex. This option can only be used with required: false and  required: only-when-needed.
• extra-allowed is a list of PCRE regexes to allow quoted string values, even if required: only-when-needed is set.
• allow-quoted-quotes allows (true) using disallowed quotes for strings with allowed quotes inside. Default false.
• check-keys defines whether to apply the rules to keys in mappings. By default, quoted-strings rules apply only to values. Set this option to true to apply the rules to keys as well.

Note: Multi-line strings (with | or >) will not be checked.

Default values (when enabled)

rules:
  quoted-strings:
    quote-type: any
    required: true
    extra-required: []
    extra-allowed: []
    allow-quoted-quotes: false
    check-keys: false

Examples

1. With quoted-strings: {quote-type: any, required: true}

   the following code snippet would PASS:

   foo: "bar"
   bar: 'foo'
   number: 123
   boolean: true

   the following code snippet would FAIL:

   foo: bar

2. With quoted-strings: {quote-type: single, required: only-when-needed}

   the following code snippet would PASS:

   foo: bar
   bar: foo
   not_number: '123'
   not_boolean: 'true'
   not_comment: '# comment'
   not_list: '[1, 2, 3]'
   not_map: '{a: 1, b: 2}'

   the following code snippet would FAIL:

   foo: 'bar'

3. With quoted-strings: {required: false, extra-required: [^http://, ^ftp://]}

   the following code snippet would PASS:

   - localhost
   - "localhost"
   - "http://localhost"
   - "ftp://localhost"

   the following code snippet would FAIL:

   - http://localhost
   - ftp://localhost

4. With quoted-strings: {required: only-when-needed, extra-allowed: [^http://, ^ftp://], extra-required: [QUOTED]}

   the following code snippet would PASS:

   - localhost
   - "http://localhost"
   - "ftp://localhost"
   - "this is a string that needs to be QUOTED"

   the following code snippet would FAIL:

   - "localhost"
   - this is a string that needs to be QUOTED

5. With quoted-strings: {quote-type: double, allow-quoted-quotes: false}

   the following code snippet would PASS:

   foo: "bar\"baz"

   the following code snippet would FAIL:

   foo: 'bar"baz'

6. With quoted-strings: {quote-type: double, allow-quoted-quotes: true}

   the following code snippet would PASS:

   foo: 'bar"baz'

7. With quoted-strings: {required: only-when-needed, check-keys: true, extra-required: ["[:]"]}

   the following code snippet would FAIL:

   foo:bar: baz

   the following code snippet would PASS:

   "foo:bar": baz

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

Use this rule to forbid non-explicitly typed truthy values other than allowed ones (by default: true and false), for example YES or off.

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

Depending on the YAML specification version used by the YAML document, the list of truthy values can differ. In YAML 1.2, only capitalized / uppercased combinations of true and false are considered truthy, whereas in YAML 1.1 combinations of yes, no, on and off are too. To make the YAML specification version explicit in a YAML document, a %YAML 1.2 directive can be used (see example below).

Options

• allowed-values defines the list of truthy values which will be ignored during linting. The default is ['true', 'false'], but can be changed to any list containing: 'TRUE', 'True',  'true', 'FALSE', 'False', 'false', 'YES', 'Yes', 'yes', 'NO', 'No', 'no', 'ON', 'On', 'on', 'OFF', 'Off', 'off'.
• check-keys disables verification for keys in mappings. By default, truthy rule applies to both keys and values. Set this option to false to prevent this.

Default values (when enabled)

rules:
  truthy:
    allowed-values: ['true', 'false']
    check-keys: true

Examples

1. With truthy: {}

   the following code snippet would PASS:

   boolean: true
   
   object: {"True": 1, 1: "True"}
   
   "yes":  1
   "on":   2
   "True": 3
   
    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:

   %YAML 1.1
   ---
   yes:  1
   on:   2
   True: 3

   the following code snippet would PASS:

   %YAML 1.2
   ---
   yes:  1
   on:   2
   true: 3

2. With truthy: {allowed-values: ["yes", "no"]}

   the following code snippet would PASS:

   - yes
   - no
   - "true"
   - 'false'
   - foo
   - bar

   the following code snippet would FAIL:

   - true
   - false
   - on
   - off

3. With truthy: {check-keys: false}

   the following code snippet would PASS:

   yes:  1
   on:   2
   true: 3

   the following code snippet would FAIL:

   yes:  Yes
   on:   On
   true: True

To prevent yamllint from reporting problems for a specific line, add a directive comment (# yamllint disable-line ...) on that line, or on the line above. For instance:

# The following mapping contains the same key twice,
# but I know what I'm doing:
- key: value 1
  key: value 2  # yamllint disable-line rule:key-duplicates

- This line is waaaaaaaaaay too long but yamllint will not report anything about it.  # yamllint disable-line rule:line-length
- This line will be checked by yamllint.

or:

# The following mapping contains the same key twice,
# but I know what I'm doing:
- key: value 1
  # yamllint disable-line rule:key-duplicates
  key: value 2

# yamllint disable-line rule:line-length
- This line is waaaaaaaaaay too long but yamllint will not report anything about it.
- This line will be checked by yamllint.

It is possible, although not recommend, to disabled all rules for a specific line:

# yamllint disable-line
-  {    all : rules ,are disabled   for this line}

You can't make yamllint ignore invalid YAML syntax on a line (which generates a syntax error), such as when templating a YAML file with Jinja. In some cases, you can workaround this by putting the templating syntax in a YAML comment. See Putting template flow control in comments.

If you need to disable multiple rules, it is allowed to chain rules like this: # yamllint disable-line rule:hyphens rule:commas rule:indentation.

To prevent yamllint from reporting problems for the whole file, or for a block of lines within the file, use # yamllint disable ... and # yamllint enable ... directive comments. For instance:

# yamllint disable rule:colons
- Lorem       : ipsum
  dolor       : sit amet,
  consectetur : adipiscing elit
# yamllint enable rule:colons

- rest of the document...

It is possible, although not recommend, to disabled all rules:

# yamllint disable
- Lorem       :
        ipsum:
          dolor : [   sit,amet]
-         consectetur : adipiscing elit
# yamllint enable

If you need to disable multiple rules, it is allowed to chain rules like this: # yamllint disable rule:hyphens rule:commas rule:indentation.

To prevent yamllint from reporting problems for a specific file, add the directive comment # yamllint disable-file as the first line of the file. For instance:

# yamllint disable-file
# The following mapping contains the same key twice, but I know what I'm doing:
- key: value 1
  key: value 2

- This line is waaaaaaaaaay too long but yamllint will not report anything about it.

or:

# yamllint disable-file
# This file is not valid YAML because it is a Jinja template
{% if extra_info %}
key1: value1
{% endif %}
key2: value2

Alternatively for templating you can wrap the template statements in comments to make it a valid YAML file. As long as the templating language doesn't use the same comment symbol, it should be a valid template and valid YAML (pre and post-template processing).

Example of a Jinja2 code that cannot be parsed as YAML because it contains invalid tokens {% and %}:

# This file IS NOT valid YAML and will produce syntax errors
{% if extra_info %}
key1: value1
{% endif %}
key2: value2

But it can be fixed using YAML comments:

# This file IS valid YAML because the Jinja is in a YAML comment
# {% if extra_info %}
key1: value1
# {% endif %}
key2: value2

yamllint provides both a script and a Python module. The latter can be used to write your own linting tools.

Basic example of running the linter from Python:

import yamllint

yaml_config = yamllint.config.YamlLintConfig("extends: default")
for p in yamllint.linter.run(open("example.yaml", "r"), yaml_config):
    print(p.desc, p.line, p.rule)

class yamllint.linter.LintProblem(line, column, desc='<no description>', rule=None)

Represents a linting problem found by yamllint.

column

Column on which the problem was found (starting at 1)

desc

Human-readable description of the problem

line

Line on which the problem was found (starting at 1)

rule

Identifier of the rule that detected the problem

yamllint.linter.run(input, conf, filepath=None)

Lints a YAML source.

Returns a generator of LintProblem objects.

Parameters

• input -- buffer, string or stream to read from
• conf -- yamllint configuration object

Most text editors support syntax checking and highlighting, to visually report syntax errors and warnings to the user. yamllint can be used to syntax-check YAML source, but a bit of configuration is required depending on your favorite text editor.

Assuming that the ALE plugin is installed, yamllint is supported by default. It is automatically enabled when editing YAML files.

If you instead use the syntastic plugin, add this to your .vimrc:

let g:syntastic_yaml_checkers = ['yamllint']

Assuming that the neomake plugin is installed, yamllint is supported by default. It is automatically enabled when editing YAML files.

If you are flycheck user, you can use flycheck-yamllint integration.

https://marketplace.visualstudio.com/items?itemName=fnando.linter

https://plugins.jetbrains.com/plugin/15349-yamllint

Help wanted!

Your favorite text editor is not listed here? Help us improve by adding a section (by opening a pull-request or issue on GitHub).

You can integrate yamllint in the pre-commit tool. Here is an example, to add in your .pre-commit-config.yaml

---
# Update the rev variable with the release version that you want, from the yamllint repo
# You can pass your custom .yamllint with args attribute.
repos:
  - repo: https://github.com/adrienverge/yamllint.git
    rev: v1.29.0
    hooks:
      - id: yamllint
        args: [--strict, -c=/path/to/.yamllint]

yamllint auto-detects when it's running inside of GitHub Actions and automatically uses the suited output format to decorate code with linting errors. You can also force the GitHub Actions output with yamllint --format github.

A minimal example workflow using GitHub Actions:

---
on: push  # yamllint disable-line rule:truthy

jobs:
  lint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3

      - name: Install yamllint
        run: pip install yamllint

      - name: Lint YAML files
        run: yamllint .

You can use the following GitLab CI/CD stage to run yamllint and get the results as a Code quality (Code Climate) <https://docs.gitlab.com/ee/ci/testing/code_quality.html> report.

---
lint:
  stage: lint
  script:
    - pip install yamllint
    - mkdir reports
    - >
      yamllint -f parsable . | tee >(awk '
      BEGIN {FS = ":"; ORS="\n"; first=1}
      {
          gsub(/^[ \t]+|[ \t]+$|"/, "", $4);
          match($4, /^\[(warning|error)\](.*)\((.*)\)$/, a);
          sev = (a[1] == "error" ? "major" : "minor");
          if (first) {
              first=0;
              printf("[");
          } else {
              printf(",");
          }
          printf("{\"location\":{\"path\":\"%s\",\"lines\":{\"begin\":%s",\
                 "\"end\":%s}},\"severity\":\"%s\",\"check_name\":\"%s\","\
                 "\"categories\":[\"Style\"],\"type\":\"issue\","\
                 "\"description\":\"%s\"}", $1, $2, $3, sev, a[3], a[2]);
      }
      END { if (!first) printf("]\n"); }' > reports/codequality.json)
  artifacts:
    when: always
    paths:
      - reports
    expire_in: 1 week
    reports:
      codequality: reports/codequality.json

You can configure yamllint to run on arc lint. Here is an example .arclint file that makes use of this configuration.

{
  "linters": {
    "yamllint": {
      "type": "script-and-regex",
      "script-and-regex.script": "yamllint",
      "script-and-regex.regex": "/^(?P<line>\\d+):(?P<offset>\\d+) +(?P<severity>warning|error) +(?P<message>.*) +\\((?P<name>.*)\\)$/m",
      "include": "(\\.(yml|yaml)$)"
    }
  }
}