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¶
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}
). Usetrue
to forbid the use of flow mappings completely. Usenon-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
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 }
With
braces: {forbid: non-empty}
the following code snippet would PASS:
object: {}
the following code snippet would FAIL:
object: { key1: 4, key2: 8 }
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 }
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 }
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: { }
With
braces: {min-spaces-inside-empty: 1, max-spaces-inside-empty: -1}
the following code snippet would PASS:
object: { }
the following code snippet would FAIL:
object: {}
brackets¶
Use this rule to control the 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]
). Usetrue
to forbid the use of flow sequences completely. Usenon-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
With
brackets: {forbid: true}
the following code snippet would PASS:
object: - 1 - 2 - abc
the following code snippet would FAIL:
object: [ 1, 2, abc ]
With
brackets: {forbid: non-empty}
the following code snippet would PASS:
object: []
the following code snippet would FAIL:
object: [ 1, 2, abc ]
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 ]
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 ]
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: [ ]
With
brackets: {min-spaces-inside-empty: 1, max-spaces-inside-empty: -1}
the following code snippet would PASS:
object: [ ]
the following code snippet would FAIL:
object: []
colons¶
Use this rule to control the number of spaces before and after colons (:
).
Options
max-spaces-before
defines the maximal number of spaces allowed before colons (use-1
to disable).max-spaces-after
defines the maximal number of spaces allowed after colons (use-1
to disable).
Default values (when enabled)
rules:
colons:
max-spaces-before: 0
max-spaces-after: 1
Examples
With
colons: {max-spaces-before: 0, max-spaces-after: 1}
the following code snippet would PASS:
object: - a - b key: value
With
colons: {max-spaces-before: 1}
the following code snippet would PASS:
object : - a - b
the following code snippet would FAIL:
object : - a - b
With
colons: {max-spaces-after: 2}
the following code snippet would PASS:
first: 1 second: 2 third: 3
the following code snippet would FAIL:
first: 1 2nd: 2 third: 3
commas¶
Use this rule to control the number of spaces before and after commas (,
).
Options
max-spaces-before
defines the maximal number of spaces allowed before commas (use-1
to disable).min-spaces-after
defines the minimal number of spaces required after commas.max-spaces-after
defines the maximal number of spaces allowed after commas (use-1
to disable).
Default values (when enabled)
rules:
commas:
max-spaces-before: 0
min-spaces-after: 1
max-spaces-after: 1
Examples
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}]
With
commas: {max-spaces-before: 2}
the following code snippet would PASS:
strange var: [10 , 20 , 30, {x: 1 , y: 2}]
With
commas: {max-spaces-before: -1}
the following code snippet would PASS:
strange var: [10, 20 , 30 , {x: 1, y: 2}]
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}]
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}]
With
commas: {min-spaces-after: 0, max-spaces-after: 1}
the following code snippet would PASS:
strange var: [10, 20,30, {x: 1, y: 2}]
comments¶
Use this rule to control the position and formatting of comments.
Options
- Use
require-starting-space
to require a space character right after the#
. Set totrue
to enable,false
to disable. - Use
ignore-shebangs
to ignore a shebang at the beginning of the file whenrequire-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
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
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
With
comments-indentation: {}
the following code snippet would PASS:
# Fibonacci [0, 1, 1, 2, 3, 5]
the following code snippet would FAIL:
# Fibonacci [0, 1, 1, 2, 3, 5]
the following code snippet would PASS:
list: - 2 - 3 # - 4 - 5
the following code snippet would FAIL:
list: - 2 - 3 # - 4 - 5
the following code snippet would PASS:
# This is the first object obj1: - item A # - item B # This is the second object obj2: []
the following code snippet would PASS:
# This sentence # is a block comment
the following code snippet would FAIL:
# This sentence # is a block comment
document-end¶
Use this rule to require or forbid the use of document end marker (...
).
Options
- Set
present
totrue
when the document end marker is required, or tofalse
when it is forbidden.
Default values (when enabled)
rules:
document-end:
present: true
Examples
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 ...
With
document-end: {present: false}
the following code snippet would PASS:
--- this: is: [a, document] --- - this - is: another one
the following code snippet would FAIL:
--- this: is: [a, document] ... --- - this - is: another one
document-start¶
Use this rule to require or forbid the use of document start marker (---
).
Options
- Set
present
totrue
when the document start marker is required, or tofalse
when it is forbidden.
Default values (when enabled)
rules:
document-start:
present: true
Examples
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
With
document-start: {present: false}
the following code snippet would PASS:
this: is: [a, document] ...
the following code snippet would FAIL:
--- this: is: [a, document] ...
empty-lines¶
Use this rule to set a maximal number of allowed consecutive blank lines.
Options
max
defines the maximal number of empty lines allowed in the document.max-start
defines the maximal number of empty lines allowed at the beginning of the file. This option takes precedence overmax
.max-end
defines the maximal number of empty lines allowed at the end of the file. This option takes precedence overmax
.
Default values (when enabled)
rules:
empty-lines:
max: 2
max-start: 0
max-end: 0
Examples
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]
empty-values¶
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.
Default values (when enabled)
rules:
empty-values:
forbid-in-block-mappings: true
forbid-in-flow-mappings: true
Examples
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:
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}
hyphens¶
Use this rule to control the number of spaces after hyphens (-
).
Options
max-spaces-after
defines the maximal number of spaces allowed after hyphens.
Default values (when enabled)
rules:
hyphens:
max-spaces-after: 1
Examples
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
With
hyphens: {max-spaces-after: 3}
the following code snippet would PASS:
- key - key2 - key42
the following code snippet would FAIL:
- key - key2 - key42
indentation¶
Use this rule to control the indentation.
Options
spaces
defines the indentation width, in spaces. Set either to an integer (e.g.2
or4
, representing the number of spaces in an indentation level) or toconsistent
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
andconsistent
.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 totrue
to enable,false
to disable.
Default values (when enabled)
rules:
indentation:
spaces: consistent
indent-sequences: true
check-multi-line-strings: false
Examples
With
indentation: {spaces: 1}
the following code snippet would PASS:
history: - name: Unix date: 1969 - name: Linux date: 1991 nest: recurse: - haystack: needle
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
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
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
With
indentation: {spaces: 2, indent-sequences: whatever}
the following code snippet would PASS:
list: - flying: - spaghetti - monster - not flying: - spaghetti - sauce
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
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
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
key-ordering¶
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 to
sort case and accents properly.
Examples
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
With global option
locale: "en_US.UTF-8"
and rulekey-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
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. Usetrue
to allow,false
to forbid.allow-non-breakable-inline-mappings
impliesallow-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
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.
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
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
With
line-length: {max: 60, allow-non-breakable-words: false}
the following code snippet would FAIL:
this: is: - a: http://localhost/very/very/very/very/very/very/very/very/long/url
new-line-at-end-of-file¶
Use this rule to require a new line character (\n
) at the end of files.
The POSIX standard requires the last line to end with a new line character. All UNIX tools expect a new line at the end of files. Most text editors use this convention too.
new-lines¶
Use this rule to force the type of new line characters.
Options
- Set
type
tounix
to use UNIX-typed new line characters (\n
), ordos
to use DOS-typed new line characters (\r\n
).
Default values (when enabled)
rules:
new-lines:
type: unix
octal-values¶
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 with0
. - Use
forbid-explicit-octal
to prevent numbers starting with0o
.
Default values (when enabled)
rules:
octal-values:
forbid-implicit-octal: true
forbid-explicit-octal: true
Examples
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
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
quoted-strings¶
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
orany
(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 withrequired: false
andrequired: only-when-needed
.extra-allowed
is a list of PCRE regexes to allow quoted string values, even ifrequired: only-when-needed
is set.
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: []
Examples
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
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'
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
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
trailing-spaces¶
Use this rule to forbid trailing spaces at the end of lines.
Examples
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 non-explictly 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}
.
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 tofalse
to prevent this.
Default values (when enabled)
rules:
truthy:
allowed-values: ['true', 'false']
check-keys: true
Examples
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:
yes: 1 on: 2 True: 3
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
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