> If you assume that YAML 1.2 is the default, you don't need that nasty %YAML header.

Indeed the YAML 1.2 spec says a document without a YAML directive should be assumed to be 1.2[1]:

> A version 1.2 YAML processor must accept documents with an explicit “%YAML 1.2” directive, as well as documents lacking a “YAML” directive. Such documents are assumed to conform to the 1.2 version specification.

It's only the YAML 1.2 spec that says it's a superset of JSON. The YAML authors weren't aware of JSON when publishing version 1.1[2]:

> The YAML 1.1 specification was published in 2005. Around this time, the developers became aware of JSON. By sheer coincidence, JSON was almost a complete subset of YAML (both syntactically and semantically).

> In 2006, Kyrylo Simonov produced PyYAML and LibYAML. A lot of the YAML frameworks in various programming languages are built over LibYAML and many others have looked to PyYAML as a solid reference for their implementations.

> The YAML 1.2 specification was published in 2009. Its primary focus was making YAML a strict superset of JSON. It also removed many of the problematic implicit typing recommendations.

The middle paragraph there is the reason this is a problem people keep running into: Most implementations are based on LibYAML, which is an implementation of YAML 1.1 that does not really support 1.2[3]. Indeed the last example from the post doesn't actually work for me on Ruby 3.4.4 with LibYAML 0.2.5. It produces the exact same output as the one before it.

[1]: https://yaml.org/spec/1.2.2/#681-yaml-directives

[2]: https://yaml.org/spec/1.2.2/#12-yaml-history

[3]: https://github.com/yaml/libyaml/issues/20

Among ecosystems based on YAML-formatted configuration defaulting to YAML 1.1 is nearly universal. The heyday of YAML was during the YAML 1.1 era, and those projects can't change their YAML parsers' default version to 1.2 without breaking extant config files.

By the time YAML 1.2 had been published and implementations written, greenfield projects were using either JSON5 (a true superset of JSON) or TOML.

  > While JSON numbers are grammatically simple, they're almost always distinct
  > from how you'd implement numbers in any language that has JSON parsers,
  > syntactically, exactness and precision-wise.

For statically-typed languages the range and precision is determined by the type of the destination value passed to the parser; it's straightforward to reject (or clamp) a JSON number `12345` being parsed into a `uint8_t`.

For dynamically-typed languages there's less emphasis on performance, so using an arbitrary-precision numeric type (Python's Decimal, Go's "math/big" types) provide lossless decoding.

The only language I know of that really struggles with JSON numbers is, ironically, JavaScript -- its BigInt type is relatively new and not well integrated with its JSON API[0], and it doesn't have an arbitrary-precision type.

[0] See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... for the incantation needed to encode a BigInt as a number.

> those who want to parse a JSON document with a YAML parser.

I've done it. We already had a YAML parser in an internal library I maintain since we were already ingesting YAML files for other reasons, so when we later added new files for a different reason that someone decided should be in JSON instead, it was easier and cleaner to keep using the existing YAML parser we already had incorporated rather than add a separate JSON parser along side it.

Anyone who wants to convert a piece at a time to yaml, but would prefer to just use a single parse step (as suggested by one of the quoted bits in the article). It's a niche case, but sensical.

You want to use a machine to create a document for something that accepts JSON. e.g. Something I was playing around with was having a github workflow that generates a github workflow. Or generating docker compose files.

It works in most trivial cases, so I'm assuming it's widely done irl.

Imagine building some small app that reads external config file. You personally only care about yaml files, but your avid users ask for official json support as well because of a few of their files.

It's not high priority, but as you remember the old saying, json is just a subset, so you try a bunch of files, confirm it works well enough, and decide to pipe JSON files to your yaml parser as well. Done and done.

And it's not so big block of code or anything that jumps at the users, the dev just happens to share a parser between formats.

Ruby on Rails has a databases.yml that is preprocessed by ERB. I often do something like:

    field: <%= File.read('/foo/bar').to_json %>

Though I have myriad criticisms of YAML, this article's arguments are not a concern at all if you can ensure that your YAML parser always uses 1.2 regardless of any %YAML directive.

Kubernetes is a good example. Objects can be read / written as json or yaml interchangeably.

Configuration systems like Kubernetes and Docker Compose use YAML parsers that accept JSON as input, allowing users to write in either format without changing the tooling.

I don’t like writing YAML. I like writing Python. So I write Python that generates YAML config files. JSON is in the standard library but YAML isn’t. So I generate JSON and name the file “file.yaml”.

GitHub Actions, Dependabot, and Docker Compose never complain.

For real. You can find hardened, optimized JSON parsers for every runtime worth running. Hard to think of why you would want to avoid all those JSON parsers and use a YAML one to parse JSON.

YAML sucking is no excuse to keep using XML. JSON, JSON5 and TOML are all great alternatives for projects.