What is the difference between YAML and JSON

Question

What are the differences between YAML and JSON  specifically considering the following things   Performance  encode decode time  Memory consumption Expression clarity Library availability  ease of use  I prefer C   I was planning to use one of these two in our embedded system to store configure files  Related  Should I use YAML or JSON to store my Perl data

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Differences    YAML  depending on how you use it  can be more readable than JSON JSON is often faster and is probably still interoperable with more systems It s possible to write a  good enough  JSON parser very quickly Duplicate keys  which are potentially valid JSON  are definitely invalid YAML  YAML has a ton of features  including comments and relational anchors   YAML syntax is accordingly quite complex  and can be hard to understand  It is possible to write recursive structures in yaml   a   amp b   b    which will loop infinitely in some converters   Even with circular detection  a  yaml bomb  is still possible  see xml bomb   Because there are no references  it is impossible to serialize complex structures with object references in JSON    YAML serialization can therefore be more efficient  In some coding environments  the use of YAML can allow an attacker to execute arbitrary code      Observations    Python programmers are generally big fans of YAML  because of the use of indentation  rather than bracketed syntax  to indicate levels     Many programmers consider the attachment of  meaning  to indentation a poor choice  If the data format will be leaving an application s environment  parsed within a UI  or sent in a messaging layer  JSON might be a better choice  YAML can be used  directly  for complex tasks like grammar definitions  and is often a better choice than inventing a new language

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If you don t need any features which YAML has and JSON doesn t  I would prefer JSON because it is very simple and is widely supported  has a lot of libraries in many languages   YAML is more complex and has less support  I don t think the parsing speed or memory use will be very much different  and maybe not a big part of your program s performance

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Sometimes you don t have to decide for one over the other    In Go  for example  you can have both at the same time   type Person struct       Name string  json  name  yaml  name       Age int  json  age  yaml  age

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From  Arnaud Lauret  Book    The Design of Web APIs        The JSON data format  JSON is a text data format based on how the JavaScript programming language describes data but is  despite its name  completely language-independent  see https   www json org    Using JSON  you can describe objects containing unordered name value pairs and also arrays or lists containing ordered values  as shown in this figure     An object is delimited by curly braces       A name is a quoted string   name   and is sep- arated from its value by a colon      A value can be a string like  value   a number like 1 23  a Boolean  true or false   the null value null  an object  or an array  An array is delimited by brackets       and its values are separated by commas      The JSON format is easily parsed using any programming language  It is also relatively easy to read and write  It is widely adopted for many uses such as databases  configura- tion files  and  of course  APIs   YAML  YAML  YAML Ain   t Markup Language  is a human-friendly  data serialization format  Like JSON  YAML  http   yaml org  is a key value data format  The figure shows a comparison of the two     Note the following points    There are no double quotes       around property names and values in YAML  JSON   s structural curly braces      and commas     are replaced by newlines and indentation in YAML  Array brackets      and commas     are replaced by dashes  -  and newlines in YAML  Unlike JSON  YAML allows comments beginning with a hash mark      It is relatively easy to convert one of those formats into the other  Be forewarned though  you will lose comments when converting a YAML document to JSON

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I find YAML to be easier on the eyes  less parenthesis      etc   Although there is the annoyance of tabs in YAML    but one gets the hang of it   In terms of performance resources  I wouldn t expect big differences between the two   Futhermore  we are talking about configuration files and so I wouldn t expect a high frequency of encode decode activity  no

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GIT and YAML  The other answers are good  Read those first  But I ll add one other reason to use YAML sometimes  git   Increasingly  many programming projects use git repositories for distribution and archival  And  while a git repo s history can equally store JSON and YAML files  the  diff  method used for tracking and displaying changes to a file is line-oriented  Since YAML is forced to be line-oriented  any small changes in a YAML file are easier to see by a human   It is true  of course  that JSON files can be  made pretty  by sorting the strings keys and adding indentation  But this is not the default and I m lazy   Personally  I generally use JSON for system-to-system interaction  I often use YAML for config files  static files  and tracked files   I also generally avoid adding YAML relational anchors  Life is too short to hunt down loops    Also  if speed and space are really a concern  I don t use either  You might want to look at BSON

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Benchmark results Below are the results of a benchmark to compare YAML vs JSON loading times  on Python and Perl JSON is much faster  at the expense of some readability  and features such as comments Test method  100 sequential runs on a fast machine  average number of seconds The dataset was a 3 44MB JSON file  containing movie data scraped from Wikipedia https   raw githubusercontent com prust wikipedia-movie-data master movies json Linked to from   https   github com jdorfman awesome-json-datasets  Results Python 3 8 3 timeit     JSON             0 108     YAML CLoader     3 684     YAML            29 763  Perl 5 26 2-043 Benchmark  cmpthese     JSON XS          0 107     YAML XS          0 574     YAML Syck        1 050  Perl 5 26 2-043 Dumbbench  Brian D Foy  excludes outliers      JSON XS          0 102     YAML XS          0 514     YAML Syck        1 027

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Technically YAML is a superset of JSON  This means that  in theory at least  a YAML parser can understand JSON  but not necessarily the other way around    See the official specs  in the section entitled  YAML  Relation to JSON    In general  there are certain things I like about YAML that are not available in JSON     As  jdupont pointed out  YAML is visually easier to look at  In fact the YAML homepage is itself valid YAML  yet it is easy for a human to read   YAML has the ability to reference other items within a YAML file using  anchors   Thus it can handle relational information as one might find in a MySQL database   YAML is more robust about embedding other serialization formats such as JSON or XML within a YAML file     In practice neither of these last two points will likely matter for things that you or I do  but in the long term  I think YAML will be a more robust and viable data serialization format    Right now  AJAX and other web technologies tend to use JSON  YAML is currently being used more for offline data processes  For example  it is included by default in the C-based OpenCV computer vision package  whereas JSON is not    You will find C libraries for both JSON and YAML  YAML s libraries tend to be newer  but I have had no trouble with them in the past  See for example Yaml-cpp

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Bypassing esoteric theory  This answers the title  not the details as most just read the title from a search result on google like me so I felt it was necessary to explain from a web developer perspective    YAML uses space indentation  which is familiar territory for Python developers  JavaScript developers love JSON because it is a subset of JavaScript and can be directly interpreted and written inside JavaScript  along with using a shorthand way to declare JSON  requiring no double quotes in keys when using typical variable names without spaces  There are a plethora of parsers that work very well in all languages for both YAML and JSON  YAML s space format can be much easier to look at in many cases because the formatting requires a more human-readable approach  YAML s form while being more compact and easier to look at can be deceptively difficult to hand edit if you don t have space formatting visible in your editor  Tabs are not spaces so that further confuses if you don t have an editor to interpret your keystrokes into spaces  JSON is much faster to serialize and deserialize because of significantly less features than YAML to check for  which enables smaller and lighter code to process JSON  A common misconception is that YAML needs less punctuation and is more compact than JSON but this is completely false  Whitespace is invisible so it seems like there are less characters  but if you count the actual whitespace which is necessary to be there for YAML to be interpreted properly along with proper indentation  you will find YAML actually requires more characters than JSON  JSON doesn t use whitespace to represent hierarchy or grouping and can be easily flattened with unnecessary whitespace removed for more compact transport    The Elephant in the room  The Internet itself  JavaScript so clearly dominates the web by a huge margin and JavaScript developers prefer using JSON as the data format overwhelmingly along with popular web APIs so it becomes difficult to argue using YAML over JSON when doing web programming in the general sense as you will likely be outvoted in a team environment  In fact  the majority of web programmers aren t even aware YAML exists  let alone consider using it   If you are doing any web programming  JSON is the default way to go because no translation step is needed when working with JavaScript so then you must come up with a better argument to use YAML over JSON in that case

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Technically YAML offers a lot more than JSON   YAML v1 2 is a superset of JSON     comments anchors and inheritance - example of 3 identical items   item1   amp anchor name   name  Test   title  Test title item2   anchor name item3     lt  lt    anchor name     You may add extra stuff         Most of the time people will not use those extra features and the main difference is that YAML uses indentation whilst JSON uses brackets  This makes YAML more concise and readable  for the trained eye    Which one to choose    YAML extra features and concise notation makes it a good choice for configuration files  non-user provided files   JSON limited features  wide support  and faster parsing makes it a great choice for interoperability and user provided data

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I find both YAML and JSON to be very effective  The only two things that really dictate when one is used over the other for me is one  what the language is used most popularly with  For example  if I m using Java  Javascript  I ll use JSON  For Java  I ll use their own objects  which are pretty much JSON but lacking in some features  and convert it to JSON if I need to or make it in JSON in the first place  I do that because that s a common thing in Java and makes it easier for other Java developers to modify my code  The second thing is whether I m using it for the program to remember attributes  or if the program is receiving instructions in the form of a config file  in this case I ll use YAML  because it s very easily human read  has nice looking syntax  and is very easy to modify  even if you have no idea how YAML works  Then  the program will read it and convert it to JSON  or whatever is preferred for that language   In the end  it honestly doesn t matter  Both JSON and YAML are easily read by any experienced programmer

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This question is 6 years old  but strangely  none of the answers really addresses all four points  speed  memory  expressiveness  portability    Speed  Obviously this is implementation-dependent  but because JSON is so widely used  and so easy to implement  it has tended to receive greater native support  and hence speed  Considering that YAML does everything that JSON does  plus a truckload more  it s likely that of any comparable implementations of both  the JSON one will be quicker   However  given that a YAML file can be slightly smaller than its JSON counterpart  due to fewer   and   characters   it s possible that a highly optimised YAML parser might be quicker in exceptional circumstances   Memory  Basically the same argument applies  It s hard to see why a YAML parser would ever be more memory efficient than a JSON parser  if they re representing the same data structure   Expressiveness  As noted by others  Python programmers tend towards preferring YAML  JavaScript programmers towards JSON  I ll make these observations    It s easy to memorise the entire syntax of JSON  and hence be very confident about understanding the meaning of any JSON file  YAML is not truly understandable by any human  The number of subtleties and edge cases is extreme  Because few parsers implement the entire spec  it s even harder to be certain about the meaning of a given expression in a given context   The lack of comments in JSON is  in practice  a real pain    Portability  It s hard to imagine a modern language without a JSON library  It s also hard to imagine a JSON parser implementing anything less than the full spec  YAML has widespread support  but is less ubiquitous than JSON  and each parser implements a different subset  Hence YAML files are less interoperable than you might think   Summary  JSON is the winner for performance  if relevant  and interoperability  YAML is better for human-maintained files  HJSON is a decent compromise although with much reduced portability  JSON5 is a more reasonable compromise  with well-defined syntax

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Since this question now features prominently when searching for YAML and JSON  it s worth noting one rarely-cited difference between the two  license  JSON purports to have a license which JSON users must adhere to  including the legally-ambiguous  shall be used for Good  not Evil    YAML carries no such license claim  and that might be an important difference  to your lawyer  if not to you

[json] What is the difference between YAML and JSON?

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