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yamllint

Linter for YAML files A linter for YAML files. yamllint does not only check for syntax validity, but for weirdnesses like key repetition and cosmetic problems such as lines length, trailing spaces …

[image: yamllint screenshot] [image]

NOTE:

The default output format is inspired by eslint, a great linting tool for Javascript.


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.


The source code of yamllint is currently hosted on GitHub at https://github.com/adrienverge/yamllint/. Releases can be found on this page.

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.


NOTE:

Files on the ignore-from-file list should use either UTF-8, UTF-16 or UTF-32. See Character Encoding for details and workarounds.


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



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



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


4.
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.

Options

  • ignored-keys is a list of PCRE regexes to ignore some keys while checking order, if they match any regex.

Default values (when enabled)

rules:
  key-ordering:
    ignored-keys: []


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


3.
With rule key-ordering: {ignored-keys: ["name"]}

the following code snippet would PASS:

- a:
  b:
  name: ignored
  first-name: ignored
  c:
  d:



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.

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»�8Qii'
   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.config
import yamllint.linter
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)


Represents a linting problem found by yamllint.
Column on which the problem was found (starting at 1)

Human-readable description of the problem

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

Identifier of the rule that detected the problem


Lints a YAML source.

Returns a generator of LintProblem objects.

  • 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) 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>.*)\\)$/m",
      "include": "(\\.(yml|yaml)$)"
    }
  }
}


When yamllint reads a file (whether its a configuration file or a file to lint), yamllint will try to automatically detect that file’s character encoding. In order for the automatic detection to work properly, files must follow these two rules (see this section of the YAML specification for details):

  • The file must be encoded in UTF-8, UTF-16 or UTF-32.
  • The file must begin with either a byte order mark or an ASCII character.

Previous versions of yamllint did not try to autodetect the character encoding of files. Previous versions of yamllint assumed that files used the current locale’s character encoding. This meant that older versions of yamllint would sometimes correctly decode files that didn’t follow those two rules. For the sake of backwards compatibility, the current version of yamllint allows you to disable automatic character encoding detection by setting the YAMLLINT_FILE_ENCODING environment variable. If you set the YAMLLINT_FILE_ENCODING environment variable to the the name of one of Python’s standard character encodings, then yamllint will use that character encoding instead of trying to autodetect the character encoding.

The YAMLLINT_FILE_ENCODING environment variable should only be used as a stopgap solution. If you need to use YAMLLINT_FILE_ENCODING, then you should really update your YAML files so that their character encoding can automatically be detected, or else you may run into compatibility problems. Future versions of yamllint may remove support for the YAMLLINT_FILE_ENCODING environment variable, and other YAML processors may misinterpret your YAML files.

Adrien Vergé

2022, Adrien Vergé