yamllint - Online in the Cloud

PROGRAM:

NAME

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 9+ / 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 sources 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, either name it .yamllint in your working directory, or
use the -c option:

yamllint -c ~/myconfig file.yaml

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: yes
min-spaces-from-content: 2
comments-indentation:
level: warning
document-end: disable
document-start:
level: warning
present: yes
empty-lines:
max: 2
max-start: 0
max-end: 0
hyphens:
max-spaces-after: 1
indentation:
spaces: consistent
indent-sequences: yes
check-multi-line-strings: no
key-duplicates: enable
line-length:
max: 80
allow-non-breakable-words: yes
new-line-at-end-of-file: enable
new-lines:
type: unix
trailing-spaces: enable

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.

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.

In both cases, the script will output them (with different colors when using the standard
output format), but the exit code can be different. More precisely, the script will exit
will a failure code only when there is one or more error(s).

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

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.
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.
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).
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).
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 yes to
enable, no 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.
1. With comments: {require-starting-space: yes}

the following code snippet would PASS:

# This sentence
# is a block comment

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 yes when the document end marker is required, or to no when it is
forbidden.
1. With document-end: {present: yes}

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: no}

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 yes when the document start marker is required, or to no when it is
forbidden.
1. With document-start: {present: yes}

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: no}

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.
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.
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: yes, no, 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 yes to enable, no to disable.
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: no}

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: yes}

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 yes to allow, no
to forbid.
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: yes}

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 splitted...

3. With line-length: {max: 60, allow-non-breakable-words: no}

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

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).

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