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# Can comments be used in JSON?

Michael Gundlach
1#
Michael Gundlach Published in 2008-10-28 20:39:03Z
 Can I use comments inside a JSON file? If so, how?
the Tin Man
2#
the Tin Man Reply to 2016-04-06 21:25:57Z
 I don't believe you can have an actual comment. The JSON should all be data, and if you include a comment, then it will be data too. You could have a designated data element called "_comment" (or something) that would be ignored by apps that use the JSON data. You would probably be better having the comment in the processes that generates/receives the JSON, as they are supposed to know what the JSON data will be in advance, or at least the structure of it. But if you decided to: { "_comment": "comment text goes here...", "glossary": { "title": "example glossary", "GlossDiv": { "title": "S", "GlossList": { "GlossEntry": { "ID": "SGML", "SortAs": "SGML", "GlossTerm": "Standard Generalized Markup Language", "Acronym": "SGML", "Abbrev": "ISO 8879:1986", "GlossDef": { "para": "A meta-markup language, used to create markup languages such as DocBook.", "GlossSeeAlso": ["GML", "XML"] }, "GlossSee": "markup" } } } } } 
Peter Mortensen
3#
Peter Mortensen Reply to 2017-01-19 17:20:33Z
 You can't. At least that's my experience from a quick glance at json.org. JSON has its syntax visualized on that page. There isn't any note about comments.
Peter Mortensen
4#
Peter Mortensen Reply to 2017-01-19 17:25:29Z
 The idea behind JSON is to provide simple data exchange between applications. These are typically web based and the language is JavaScript. It doesn't really allow for comments as such, however, passing a comment as one of the name/value pairs in the data would certainly work, although that data would obviously need to be ignored or handled specifically by the parsing code. All that said, it's not the intention that the JSON file should contain comments in the traditional sense. It should just be the data. Have a look at the JSON website for more detail.
Kasun Randika
5#
Kasun Randika Reply to 2015-08-29 17:51:26Z
 If your text file, which is a JSON string, is going to be read by some program, how difficult would it be to strip out either C or C++ style comments before using it? Answer: It would be a one liner. If you do that then JSON files could be used as configuration files.
Kyle Simpson
6#
Kyle Simpson Reply to 2017-01-20 13:40:10Z
 Include comments if you choose; strip them out with a minifier before parsing or transmitting. I just released JSON.minify() which strips out comments and whitespace from a block of JSON and makes it valid JSON that can be parsed. So, you might use it like: JSON.parse(JSON.minify(my_str));  When I released it, I got a huge backlash of people disagreeing with even the idea of it, so I decided that I'd write a comprehensive blog post on why comments make sense in JSON. It includes this notable comment from the creator of JSON: Suppose you are using JSON to keep configuration files, which you would like to annotate. Go ahead and insert all the comments you like. Then pipe it through JSMin before handing it to your JSON parser. - Douglas Crockford, 2012 Hopefully that's helpful to those who disagree with why JSON.minify() could be useful.
Peter Mortensen
7#
Peter Mortensen Reply to 2017-01-19 17:37:30Z
 You should write a JSON schema instead. JSON schema is currently a proposed Internet draft specification. Besides documentation, the schema can also be used for validating your JSON data. Example: { "description":"A person", "type":"object", "properties": { "name": { "type":"string" }, "age": { "type":"integer", "maximum":125 } } }  You can provide documentation by using the description schema attribute.
stakx
8#
 No, comments of the form //… or /*…*/ are not allowed in JSON. This answer is based on: http://www.json.org RFC 4627: The application/json Media Type for JavaScript Object Notation (JSON) RFC 7159 The JavaScript Object Notation (JSON) Data Interchange Format - Obsoletes: 4627, 7158
Peter Mortensen
9#
Peter Mortensen Reply to 2017-01-19 17:39:46Z
 The Dojo Toolkit JavaScript toolkit (at least as of version 1.4), allows you to include comments in your JSON. The comments can be of /* */ format. Dojo Toolkit consumes the JSON via the dojo.xhrGet() call. Other JavaScript toolkits may work similarly. This can be helpful when experimenting with alternate data structures (or even data lists) before choosing a final option.
Peter Mortensen
10#
Peter Mortensen Reply to 2017-01-19 17:42:10Z
 I just encountering this for configuration files. I don't want to use XML (verbose, graphically, ugly, hard to read), or "ini" format (no hierarchy, no real standard, etc.) or Java "Properties" format (like .ini). JSON can do all they can do, but it is way less verbose and more human readable - and parsers are easy and ubiquitous in many languages. It's just a tree of data. But out-of-band comments are a necessity often to document "default" configurations and the like. Configurations are never to be "full documents", but trees of saved data that can be human readable when needed. I guess one could use "#": "comment", for "valid" JSON.
Marnen Laibow-Koser
11#
Marnen Laibow-Koser Reply to 2011-08-31 02:24:26Z
 Consider using YAML. It's nearly a superset of JSON (virtually all valid JSON is valid YAML) and it allows comments.
Peter Mortensen
12#
Peter Mortensen Reply to 2017-01-19 17:46:32Z
 Comments are not an official standard. Although some parsers support C-style comments. One that I use is JsonCpp. In the examples there is this one: // Configuration options { // Default encoding for text "encoding" : "UTF-8", // Plug-ins loaded at start-up "plug-ins" : [ "python", "c++", "ruby" ], // Tab indent size "indent" : { "length" : 3, "use_space": true } }  jsonlint does not validate this. So comments are a parser specific extension and not standard. Another parser is JSON5. An alternative to JSON TOML.
hakre
13#
 Comments were removed from JSON by design. I removed comments from JSON because I saw people were using them to hold parsing directives, a practice which would have destroyed interoperability. I know that the lack of comments makes some people sad, but it shouldn't. Suppose you are using JSON to keep configuration files, which you would like to annotate. Go ahead and insert all the comments you like. Then pipe it through JSMin before handing it to your JSON parser. Source: Public statement by Douglas Crockford on G+
Community
14#
 It depends on your JSON library. Json.NET supports JavaScript-style comments, /* commment */. See another Stack Overflow question.
Peter Mortensen
15#
Peter Mortensen Reply to 2017-01-19 17:53:45Z
 Sorry, we can't use comments in JSON... See the syntax diagram for JSON on JSON.org. Douglas Crockford says "why he removed comments in JSON and providing an alternative way to do that": I removed comments from JSON because I saw people were using them to hold parsing directives, a practice which would have destroyed interoperability. I know that the lack of comments makes some people sad, but it shouldn't. Suppose you are using JSON to keep configuration files, which you would like to annotate. Go ahead and insert all the comments you like. Then pipe it through JSMin before handing it to your JSON parser.
Basel Shishani
16#
Basel Shishani Reply to 2013-01-25 14:45:56Z
gaborous
17#
 JSON does not support comments natively, but you can make your own decoder or at least preprocessor to strip out comments, that's perfectly fine (as long as you just ignore comments and don't use them to guide how your application should process the JSON data). JSON does not have comments. A JSON encoder MUST NOT output comments. A JSON decoder MAY accept and ignore comments. Comments should never be used to transmit anything meaningful. That is what JSON is for. Cf: Douglas Crockford, author of JSON spec.
thanksd
18#
 DISCLAIMER: YOUR WARRANTY IS VOID As has been pointed out, this hack takes advantage of the implementation of the spec. Not all JSON parsers will understand this sort of JSON. Streaming parsers in particular will choke. It's an interesting curiosity, but you should really not be using it for anything at all. Below is the original answer. I've found a little hack that allows you to place comments in a JSON file that will not affect the parsing, or alter the data being represented in any way. It appears that when declaring an object literal you can specify two values with the same key, and the last one takes precedence. Believe it or not, it turns out that JSON parsers work the same way. So we can use this to create comments in the source JSON that will not be present in a parsed object representation. ({a: 1, a: 2}); // => Object {a: 2} Object.keys(JSON.parse('{"a": 1, "a": 2}')).length; // => 1  If we apply this technique, your commented JSON file might look like this: { "api_host" : "The hostname of your API server. You may also specify the port.", "api_host" : "hodorhodor.com", "retry_interval" : "The interval in seconds between retrying failed API calls", "retry_interval" : 10, "auth_token" : "The authentication token. It is available in your developer dashboard under 'Settings'", "auth_token" : "5ad0eb93697215bc0d48a7b69aa6fb8b", "favorite_numbers": "An array containing my all-time favorite numbers", "favorite_numbers": [19, 13, 53] }  The above code is valid JSON. If you parse it, you'll get an object like this: { "api_host": "hodorhodor.com", "retry_interval": 10, "auth_token": "5ad0eb93697215bc0d48a7b69aa6fb8b", "favorite_numbers": [19,13,53] }  Which means there is no trace of the comments, and they won't have weird side-effects. Happy hacking!
Peter Mortensen
19#
Peter Mortensen Reply to 2017-01-19 18:00:16Z
 You can have comments in JSONP, but not in pure JSON. I've just spent an hour trying to make my program work with this example from Highcharts: http://www.highcharts.com/samples/data/jsonp.php?filename=aapl-c.json&callback=? If you follow the link, you will see ?(/* AAPL historical OHLC data from the Google Finance API */ [ /* May 2006 */ [1147651200000,67.79], [1147737600000,64.98], ... [1368057600000,456.77], [1368144000000,452.97] ]);  Since I had a similar file in my local folder, there were no issues with the Same-origin policy, so I decided to use pure JSON... and, of course, $.getJSON was failing silently because of the comments. Eventually I just sent a manual HTTP request to the address above and realized that the content-type was text/javascript since, well, JSONP returns pure JavaScript. In this case comments are allowed. But my application returned content-type application/json, so I had to remove the comments. Peter Mortensen 20# Peter Mortensen Reply to 2017-01-19 18:01:59Z  To cut a JSON item into parts I add "dummy comment" lines: { "#############################" : "Part1", "data1" : "value1", "data2" : "value2", "#############################" : "Part2", "data4" : "value3", "data3" : "value4" }  Steve Thomas 21# Steve Thomas Reply to 2013-11-28 13:48:59Z  Sigh. Why not just add fields, e.g. { "note1" : "This demonstrates the provision of annotations within a JSON file", "field1" : 12, "field2" : "some text", "note2" : "Add more annotations as necessary" }  Just make sure your "notex" names don't conflict with any real fields. Joshua Richardson 22# Joshua Richardson Reply to 2013-12-11 23:59:51Z  The author of JSON wants us to include comments in the JSON, but strip them out before parsing them (see link provided by Michael Burr.) If JSON should have comments, why not standardize them, and let the JSON parser do the job? I don't agree with the logic there, but, alas, that's the standard. Using YAML solution as suggested by others is good, but requires library dependency. If you want to strip out comments, but don't want to have a library dependency, here is a two-line solution, which works for C++-style comments, but can be adapted to others: var comments=new RegExp("//.*", 'mg'); data = JSON.parse(fs.readFileSync(sample_file, 'utf8').replace(comments, ''));  Note that this solution can only be used in cases where you can be sure that the JSON data does not contain the comment initiator, e.g. ('//'). Another way to achieve JSON parsing, stripping of comments, and no extra library, is to evaluate the JSON in a JS interpreter. The caveat with that approach, of course, is that you would only want to evaluate untainted data (no untrusted user-input.) Here is an example of this approach in node.js -- another caveat, following example will only read the data once and then it will be cached: data = require(fs.realpathSync(doctree_fp));  Ondrej 23# Ondrej Reply to 2017-10-24 09:25:48Z  There is a good solution (hack), which is valid JSON. Just make the same key twice (or more). For example: { "param" : "This is the comment place", "param" : "This is value place", }  So JSON will understand this as: { "param" : "This is value place", }  Andrejs 24# Andrejs Reply to 2017-02-21 12:48:15Z  If you are using Jackson as your JSON parser then this is how you enable it to allow comments: ObjectMapper mapper = new ObjectMapper().configure(Feature.ALLOW_COMMENTS, true);  Then you can have comments like this: { key: "value" // comment }  And you can also have comments starting with # by setting: mapper.configure(Feature.ALLOW_YAML_COMMENTS, true);  But in general (as answered before) the spec does not allow comments. laktak 25# laktak Reply to 2016-08-09 21:20:28Z  JSON does not support comments. It was also never intended to be used for configuration files where comments would be needed. Hjson is a configuration file format for humans. Relaxed syntax, fewer mistakes, more comments. See hjson.org for JavaScript, Java, Python, PHP, Rust, Go, Ruby and C# libraries. Full Decent 26# Full Decent Reply to 2015-12-15 05:53:41Z  This is a "can you" question. And here is a "yes" answer. No, you shouldn't use duplicative object members to stuff side channel data into a JSON encoding. (See "The names within an object SHOULD be unique" in the RFC). And yes, you could insert comments around the JSON, which you could parse out. But if you want a way of inserting and extracting arbitrary side-channel data to a valid JSON, here is an answer. We take advantage of the non-unique representation of data in a JSON encoding. This is allowed* in section two of the RFC under "whitespace is allowed before or after any of the six structural characters". *The RFC only states "whitespace is allowed before or after any of the six structural characters", not explicitly mentioning strings, numbers, "false", "true", and "null". This omission is ignored in ALL implementations. First, canonicalize your JSON by minifying it: $jsonMin = json_encode(json_decode($json));  Then encode your comment in binary: $hex = unpack('H*', $comment);$commentBinary = base_convert($hex[1], 16, 2);  Then steg your binary: $steg = str_replace('0', ' ', $commentBinary);$steg = str_replace('1', "\t", $steg);  Here is your output: $jsonWithComment = $steg .$jsonMin; 
Peter Mortensen
27#
Peter Mortensen Reply to 2017-01-19 18:17:26Z
 I just found "grunt-strip-json-comments". “Strip comments from JSON. It lets you use comments in your JSON files!” { // Rainbows "unicorn": /* ❤ */ "cake" } 
Peter Mortensen
28#
Peter Mortensen Reply to 2017-01-19 18:19:01Z
 Yes, you can, but your parse will probably fail (there is no standard). To parse it you should remove those comments, or by hand, or using a regular expression: It replaces any comments, like: /**** * Hey */ /\/\*([^*]|[\r\n]|(\*+([^*/]|[\r\n])))*\*\/+/  It replaces any comments, like: // Hey /\/\/.*/  In JavaScript, you could do something like this: jsonString = jsonString.replace(/\/\*([^*]|[\r\n]|(\*+([^*/]|[\r\n])))*\*\/+/, "").replace(/\/\/.*/,"") var object = JSON.parse(jsonString); 
toolbear
29#
 If your context is Node.js configuration, you might consider JavaScript via module.exports as an alternative to JSON: module.exports = { "key": "value", // And with comments! "key2": "value2" };  The require syntax will still be the same. Being JavaScript, the file extension should be .js.
 We are using strip-json-comments for our project. It supports something like: /* * Description */ { // rainbows "unicorn": /* ❤ */ "cake" }  Simply npm install --save strip-json-comments to install and use it like: var strip_json_comments = require('strip-json-comments') var json = '{/*rainbows*/"unicorn":"cake"}'; JSON.parse(strip_json_comments(json)); //=> {unicorn: 'cake'}