yamllint man page

yamllint —

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, indentation, etc.

Screenshot

[image: yamllint screenshot] [image]

NOTE:

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

Table of Contents

Quickstart

Installing yamllint

On Fedora / CentOS:

sudo dnf install yamllint

On Debian 8+ / Ubuntu 16.04+:

sudo apt-get install yamllint

On older Debian / Ubuntu versions:

sudo add-apt-repository -y ppa:adrienverge/ppa && sudo apt-get update
sudo apt-get install yamllint

Alternatively using pip, the Python package manager:

sudo pip install yamllint

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

python setup.py sdist
sudo pip install dist/yamllint-*.tar.gz

Running yamllint

Basic usage:

yamllint file.yml other-file.yaml

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

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)

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.

Configuration

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):

·
.yamllint in the current working directory
·
$XDG_CONFIG_HOME/yamllint/config
·
~/.config/yamllint/config

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

Default configuration

Unless told otherwise, yamllint uses its default configuration:

---

rules:
  braces:
    min-spaces-inside: 0
    max-spaces-inside: 0
  brackets:
    min-spaces-inside: 0
    max-spaces-inside: 0
  colons:
    max-spaces-before: 0
    max-spaces-after: 1
  commas:
    max-spaces-before: 0
    min-spaces-after: 1
    max-spaces-after: 1
  comments:
    level: warning
    require-starting-space: true
    min-spaces-from-content: 2
  comments-indentation:
    level: warning
  document-end: disable
  document-start:
    level: warning
    present: true
  empty-lines:
    max: 2
    max-start: 0
    max-end: 0
  hyphens:
    max-spaces-after: 1
  indentation:
    spaces: consistent
    indent-sequences: true
    check-multi-line-strings: false
  key-duplicates: enable
  line-length:
    max: 80
    allow-non-breakable-words: true
    allow-non-breakable-inline-mappings: false
  new-line-at-end-of-file: enable
  new-lines:
    type: unix
  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

Extending the default configuration

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

Custom configuration without a config file

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

Errors and warnings

Problems detected by yamllint can be raised either as errors or as warnings. The CLI will output them (with different colors when using the standard output format).

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

Rules

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

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

This page describes the rules and their options.

List of rules

·
braces
·
brackets
·
colons
·
commas
·
comments
·
comments-indentation
·
document-end
·
document-start
·
empty-lines
·
hyphens
·
indentation
·
key-duplicates
·
line-length
·
new-line-at-end-of-file
·
new-lines
·
trailing-spaces
·
truthy

braces

Use this rule to control the number of spaces inside braces ({ and }). Options.INDENT 0.0

·
min-spaces-inside defines the minimal number of spaces required inside braces.
·
max-spaces-inside defines the maximal number of spaces allowed inside braces. Examples.INDENT 0.0
1.

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

the following code snippet would PASS:

object: {key1: 4, key2: 8}

the following code snippet would FAIL:

object: { key1: 4, key2: 8 }
2.

With braces: {min-spaces-inside: 1, max-spaces-inside: 3}

the following code snippet would PASS:

object: { key1: 4, key2: 8 }

the following code snippet would PASS:

object: { key1: 4, key2: 8   }

the following code snippet would FAIL:

object: {    key1: 4, key2: 8   }

the following code snippet would FAIL:

object: {key1: 4, key2: 8 }

brackets

Use this rule to control the number of spaces inside brackets ([ and ]). Options.INDENT 0.0

·
min-spaces-inside defines the minimal number of spaces required inside brackets.
·
max-spaces-inside defines the maximal number of spaces allowed inside brackets. Examples.INDENT 0.0
1.

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

the following code snippet would PASS:

object: [1, 2, abc]

the following code snippet would FAIL:

object: [ 1, 2, abc ]
2.

With brackets: {min-spaces-inside: 1, max-spaces-inside: 3}

the following code snippet would PASS:

object: [ 1, 2, abc ]

the following code snippet would PASS:

object: [ 1, 2, abc   ]

the following code snippet would FAIL:

object: [    1, 2, abc   ]

the following code snippet would FAIL:

object: [1, 2, abc ]

colons

Use this rule to control the number of spaces before and after colons (:). Options.INDENT 0.0

·
max-spaces-before defines the maximal number of spaces allowed before colons (use -1 to disable).
·
max-spaces-after defines the maximal number of spaces allowed after colons (use -1 to disable). Examples.INDENT 0.0
1.

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

the following code snippet would PASS:

object:
  - a
  - b
key: value
2.

With colons: {max-spaces-before: 1}

the following code snippet would PASS:

object :
  - a
  - b

the following code snippet would FAIL:

object  :
  - a
  - b
3.

With colons: {max-spaces-after: 2}

the following code snippet would PASS:

first:  1
second: 2
third:  3

the following code snippet would FAIL:

first: 1
2nd:   2
third: 3

commas

Use this rule to control the number of spaces before and after commas (,). Options.INDENT 0.0

·
max-spaces-before defines the maximal number of spaces allowed before commas (use -1 to disable).
·
min-spaces-after defines the minimal number of spaces required after commas.
·
max-spaces-after defines the maximal number of spaces allowed after commas (use -1 to disable). Examples.INDENT 0.0
1.

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

the following code snippet would PASS:

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

the following code snippet would FAIL:

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

With commas: {max-spaces-before: 2}

the following code snippet would PASS:

strange var:
  [10  , 20 , 30,  {x: 1  , y: 2}]
3.

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

the following code snippet would PASS:

strange var:
  [10,
   20   , 30
   ,   {x: 1, y: 2}]
4.

With commas: {min-spaces-after: 1, max-spaces-after: 1}

the following code snippet would PASS:

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

the following code snippet would FAIL:

strange var:
  [10, 20,30,   {x: 1,   y: 2}]
5.

With commas: {min-spaces-after: 1, max-spaces-after: 3}

the following code snippet would PASS:

strange var:
  [10, 20,  30,  {x: 1,   y: 2}]
6.

With commas: {min-spaces-after: 0, max-spaces-after: 1}

the following code snippet would PASS:

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

comments

Use this rule to control the position and formatting of comments. Options.INDENT 0.0

·
Use require-starting-space to require a space character right after the #. Set to true to enable, false to disable.
·
min-spaces-from-content is used to visually separate inline comments from content. It defines the minimal required number of spaces between a comment and its preceding content. Examples.INDENT 0.0
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.INDENT 0.0

1.

With comments-indentation: {}

the following code snippet would PASS:

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

the following code snippet would FAIL:

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

the following code snippet would PASS:

list:
    - 2
    - 3
    # - 4
    - 5

the following code snippet would FAIL:

list:
    - 2
    - 3
#    - 4
    - 5

the following code snippet would PASS:

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

the following code snippet would PASS:

# This sentence
# is a block comment

the following code snippet would FAIL:

# This sentence
 # is a block comment

document-end

Use this rule to require or forbid the use of document end marker (...). Options.INDENT 0.0

·
Set present to true when the document end marker is required, or to false when it is forbidden. Examples.INDENT 0.0
1.

With document-end: {present: true}

the following code snippet would PASS:

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

the following code snippet would FAIL:

---
this:
  is: [a, document]
---
- this
- is: another one
...
2.

With document-end: {present: false}

the following code snippet would PASS:

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

the following code snippet would FAIL:

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

document-start

Use this rule to require or forbid the use of document start marker (---). Options.INDENT 0.0

·
Set present to true when the document start marker is required, or to false when it is forbidden. Examples.INDENT 0.0
1.

With document-start: {present: true}

the following code snippet would PASS:

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

the following code snippet would FAIL:

this:
  is: [a, document]
---
- this
- is: another one
2.

With document-start: {present: false}

the following code snippet would PASS:

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

the following code snippet would FAIL:

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

empty-lines

Use this rule to set a maximal number of allowed consecutive blank lines. Options.INDENT 0.0

·
max defines the maximal number of empty lines allowed in the document.
·
max-start defines the maximal number of empty lines allowed at the beginning of the file. This option takes precedence over max.
·
max-end defines the maximal number of empty lines allowed at the end of the file. This option takes precedence over max. Examples.INDENT 0.0
1.

With empty-lines: {max: 1}

the following code snippet would PASS:

- foo:
    - 1
    - 2

- bar: [3, 4]

the following code snippet would FAIL:

- foo:
    - 1
    - 2


- bar: [3, 4]

hyphens

Use this rule to control the number of spaces after hyphens (-). Options.INDENT 0.0

·
max-spaces-after defines the maximal number of spaces allowed after hyphens. Examples.INDENT 0.0
1.

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

the following code snippet would PASS:

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

the following code snippet would FAIL:

-  first list:
     - a
     - b

the following code snippet would FAIL:

- - 1
  -  2
  - 3
2.

With hyphens: {max-spaces-after: 3}

the following code snippet would PASS:

-   key
-  key2
- key42

the following code snippet would FAIL:

-    key
-   key2
-  key42

indentation

Use this rule to control the indentation. Options.INDENT 0.0

·
spaces defines the indentation width, in spaces. Set either to an integer (e.g. 2 or 4, representing the number of spaces in an indentation level) or to consistent to allow any number, as long as it remains the same within the file.
·
indent-sequences defines whether block sequences should be indented or not (when in a mapping, this indentation is not mandatory -- some people perceive the - as part of the indentation). Possible values: true, false, whatever and consistent. consistent requires either all block sequences to be indented, or none to be. whatever means either indenting or not indenting individual block sequences is OK.
·
check-multi-line-strings defines whether to lint indentation in multi-line strings. Set to true to enable, false to disable. Examples.INDENT 0.0
1.

With indentation: {spaces: 1}

the following code snippet would PASS:

history:
 - name: Unix
   date: 1969
 - name: Linux
   date: 1991
nest:
 recurse:
  - haystack:
     needle
2.

With indentation: {spaces: 4}

the following code snippet would PASS:

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

the following code snippet would FAIL:

history:
  - name: Unix
    date: 1969
  - name: Linux
    date: 1991
nest:
  recurse:
    - haystack:
        needle
3.

With indentation: {spaces: consistent}

the following code snippet would PASS:

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

the following code snippet would FAIL:

some:
  Russian:
      dolls
4.

With indentation: {spaces: 2, indent-sequences: false}

the following code snippet would PASS:

list:
- flying
- spaghetti
- monster

the following code snippet would FAIL:

list:
  - flying
  - spaghetti
  - monster
5.

With indentation: {spaces: 2, indent-sequences: whatever}

the following code snippet would PASS:

list:
- flying:
  - spaghetti
  - monster
- not flying:
    - spaghetti
    - sauce
6.

With indentation: {spaces: 2, indent-sequences: consistent}

the following code snippet would PASS:

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

the following code snippet would FAIL:

- flying:
    - spaghetti
    - monster
- not flying:
  - spaghetti
  - sauce
7.

With indentation: {spaces: 4, check-multi-line-strings: true}

the following code snippet would PASS:

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

the following code snippet would PASS:

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

the following code snippet would FAIL:

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

the following code snippet would FAIL:

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

the following code snippet would PASS:

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

key-duplicates

Use this rule to prevent multiple entries with the same key in mappings. Examples.INDENT 0.0

1.

With key-duplicates: {}

the following code snippet would PASS:

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

the following code snippet would FAIL:

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

the following code snippet would FAIL:

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

the following code snippet would FAIL:

duplicated key: 1
"duplicated key": 2

other duplication: 1
? >-
    other
    duplication
: 2

line-length

Use this rule to set a limit to lines length. Options.INDENT 0.0

·
max defines the maximal (inclusive) length of lines.
·
allow-non-breakable-words is used to allow non breakable words (without spaces inside) to overflow the limit. This is useful for long URLs, for instance. Use true to allow, false to forbid.
·
allow-non-breakable-inline-mappings implies allow-non-breakable-words and extends it to also allow non-breakable words in inline mappings. Examples.INDENT 0.0
1.

With line-length: {max: 70}

the following code snippet would PASS:

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

the following code snippet would FAIL:

long sentence:
  Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
  tempor incididunt ut labore et dolore magna aliqua.
2.

With line-length: {max: 60, allow-non-breakable-words: true}

the following code snippet would PASS:

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

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

the following code snippet would FAIL:

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

and the following code snippet would also FAIL:

- foobar: http://localhost/very/very/very/very/very/very/very/very/long/url
3.

With line-length: {max: 60, allow-non-breakable-words: true, allow-non-breakable-inline-mappings: true}

the following code snippet would PASS:

- foobar: http://localhost/very/very/very/very/very/very/very/very/long/url
4.

With line-length: {max: 60, allow-non-breakable-words: false}

the following code snippet would FAIL:

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

new-line-at-end-of-file

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

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

new-lines

Use this rule to force the type of new line characters. Options.INDENT 0.0

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

trailing-spaces

Use this rule to forbid trailing spaces at the end of lines. Examples.INDENT 0.0

1.

With trailing-spaces: {}

the following code snippet would PASS:

this document doesn't contain
any trailing
spaces

the following code snippet would FAIL:

this document contains     
trailing spaces
on lines 1 and 3

truthy

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

This would prevent YAML parsers from transforming [yes, FALSE, Off] into [true, false, false] or {y: 1, yes: 2, on: 3, true: 4, True: 5} into {y: 1, true: 5}. Examples.INDENT 0.0

1.

With truthy: {}

the following code snippet would PASS:

boolean: true

object: {"True": 1, 1: "True"}

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

 explicit:
   string1: !!str True
   string2: !!str yes
   string3: !!str off
   encoded: !!binary |
              True
              OFF
              pad==  # this decodes as 'N»ž8Qii'
   boolean1: !!bool true
   boolean2: !!bool "false"
   boolean3: !!bool FALSE
   boolean4: !!bool True
   boolean5: !!bool off
   boolean6: !!bool NO

the following code snippet would FAIL:

object: {True: 1, 1: True}

the following code snippet would FAIL:

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

Disable with comments

Disabling checks for a specific line

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

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

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

Disabling checks for all (or part of) the file

To prevent yamllint from reporting problems for the whoe file, or for a block of lines within the file, use # yamllint disable ... and # yamllint enable

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

- rest of the document...

It it 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.

Development

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

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

Represents a linting problem found by yamllint.

column = None
Column on which the problem was found (starting at 1)
desc = None
Human-readable description of the problem
line = None
Line on which the problem was found (starting at 1)
rule = None
Identifier of the rule that detected the problem
yamllint.linter.run(input, conf)

Lints a YAML source.

Returns a generator of LintProblem objects.

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

Integration with text editors

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.

Vim

Assuming that the syntastic plugin is installed, add to your .vimrc:

let g:syntastic_yaml_checkers = ['yamllint']

Neovim

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

Other text editors

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).

Author

Adrien Vergé

Info

Nov 30, 2016 1.6.0 yamllint