1 yr. ago • 100%

What is the best file format for configuration file?

.yaml, .toml, etc?

47 comments

I usually use Json5. It's JSON, but with all the weird quirks fixed (comments added, you can use hex numbers, you can have trailing commas etc.)

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- Oh that's interesting. Wonder how many libraries out there support it...
  
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  I don't know if it's actual json5, but eslint and some other libraries use extended, commentable json in their config files.
  
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A lot of good answers but I would add one note:

use a format that supports comments, and JSON is not one of those...
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- Permanently Deleted
  
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  You disgust me
  
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  This is actually pretty genius, why haven't ever thought of that?
  
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  How do you comment multiple properties separately?
  
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- I believe the JSON deserializer .NET ships with has options to allow C#-style comments in JSON files.
  
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- JSON5 is a superset of JSON that supports comments.
  
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- json with comments can be parsed by a yaml parser. It's how I write yaml, in fact (yaml is a superset of json. any valid json is valid yaml, but it also supports comments)
  
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JSON by a mile. I hate the YAML plague, it’s some of the most unintuitive syntax I’ve seen and yet it’s everywhere in DevOps/SysOps.

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- The only thing that really annoys me about JSON is that it doesn't allow comments.
  
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  JSON5, bay-beee
  
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- GitHub Actions and Azure DevOps had me hating on YAML pretty quickly
  
  6
- Yeah, any language in which whitespace count is semantically significant can go suck fat nards.
  
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  I mean, a valid JSON is a valid YAML
  
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  Not sure whether fantastic troll or just no exposure to Python.
  
  Either way....I'm here for it.
  
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- YAML works better with git than JSON, but so much config work is copy and pasting and YAML is horrible at that.
  
  Having something where changing one line doesn't turn into changing three lines, but you could also copy it off a website would be great.
  
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It depends what you need your configuration file to be:

Need a well defined easy to understand concrete configuration file?

Use .toml. It was made to be both human and computer friendly while taking special attention to avoid the pitfalls commonly found in other configuration files by explicitly stating expected types around commonly confused areas.

Need a simple to implement configuration file?

Use .json. It's famous for being so simple it's ~~creator~~ "discoverer" could define it on a business card.

Need an abstract configuration file for more complicated setups?

Use .ncl. Nickle allows you to define functions so that you can generate/compute the correct configuration by changing a few variables/flags.
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.ini

ducks

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- Give the windows registry a shot.
  
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Permanently Deleted

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Yaml for me, I really like it. And the fact that every valid JSON is also a valid YAML is nice.

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- YAML here as well.
  
  Configuration many levels deep gets so much harder for me to read and write in JSON with all [], {} and ""
  
  Also the lack of comments... And YAML still is more used in software I'm using than JSON5, so I'd rather skip yet another format/library to keep track of.
  
  3
- Please do not use YAML. It's a syntactic minefield. It also doesn't allow tab indentation, which is supremely irritating.
  
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  As I said, I like it the most, so I will use it. I like its syntax (except for yes and no for booleans, but nothing's perfect). I don't care much for tabs vs spaces, I use tab in my IDE and whatever it does, it does.
  
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https://nestedtext.org/

It's like yaml but simple, consistent, untyped, and you never need to escape any characters, ever.

Types and validation aren't going to be great unless they're in the actual code anyway.

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- Agreed.
  
  I honestly don't understand anyone who likes json over it. Json is fine for certain things but manually typing that is pain ten times over. It's better than XML surely but not by terribly much.
  
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The one with a validator provided to the user.

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No reason to go beyond simple key-value format like dotenv or just env variables. If you need more structure then maybe you are confusing configuration with state and this is not really the same thing.

7
It really depends. I usually prefer json. It's easily understandable from humans and from machines, it doesn't depends on indentation and above everything else I like it very much 🤣

6
Depends on what you mean exactly with "file format".

If declarative functional programming falls under that, I think something like Nickel, the already mentioned Dhall or Nix. Though Nix more so for packaging and some kind of system management (NixOS?), it's not easily embeddable into a runtime (your app?). Nickel or Dhall is better for that, as they are built from ground up with that in mind, Nickel is maybe the successor of Nix as it is inspired by Dhall and Nix (one goal is to use Nickel as frontend).

The reason why I recommend a simple declarative language, is that they are IMHO much better composable as it lets the user hide boilerplate via functions. I almost always feel limited by static configuration formats like yaml, json etc..

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Dhall

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- Bruh. I want to use this for my dotfiles. Thanks for sharing it!
  
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  You might want to checkout NixOS (or home-manager if you don't want a cold deep dive into a rabbit-hole).
  
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.xml

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- XML would be great if it wasn't for the extended XML universe of namespaces and imports.
  
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Need it to be user editable in a text editor? YAML. Otherwise, JSON.

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I think it's YAML.

I'm not happy that it's YAML but it's become ubiquitous. Sure, there are lots of other formats that others have mentioned, but I'm sorry most of them are positioned as "it's better than YAML!" and the fact that everyone is mentioning YAML, even if it's about the things it does wrong (and boy does it do things wrong) still means that YAML is on everyone's mind.

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Whatever. Comments are helpful, which makes pure JSON a poor choice. JSON5 or JSON-C are better, but linting and static analysis are important to every form of code, so make sure that what you use for that will understand your syntax.

My current preference is generally TOML, but I've started dabbling with custom HCL2 DSLs. (I write a lot of Go and Terraform.)

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Might be somewhat partial to CueLang but that needs an external tool to fiddle with.

I mostly use YAML or TOML depending on what's being configured.

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Tyson is nice - esp. if you are already using TS/JS.

https://github.com/jetpack-io/tyson

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