Reorganize YAML licensing post with comprehensive table format
Replace scattered sections with single table covering all 42 languages. Table shows language, library, license, and notes in scannable format. Condense pattern analysis to reference table. Reduce post length by 40% while preserving all key information.
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@ -21,285 +21,98 @@ the question
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Every programming language needs a YAML parser. But who controls the code? What licenses apply? Can you use them commercially? What restrictions exist?
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After researching YAML implementations across 42 languages (the same count as in the `webwords project </webwords-reaches-42-languages-the-ultimate-programming-kata>`_), patterns emerged.
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After researching YAML implementations across 42 languages (the same count as in the `webwords project </webwords-reaches-42-languages-the-ultimate-programming-kata>`_), clear patterns emerged.
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the foundation: libyaml
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========================
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the foundation
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==============
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Most YAML parsers trace back to **libyaml** - the canonical C implementation.
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Most YAML parsers trace back to **libyaml** - the canonical C implementation written by Kirill Simonov & maintained by the YAML community.
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**License: MIT**
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libyaml was written by Kirill Simonov & is now maintained by the YAML community. The MIT license means you can use it anywhere, modify it freely, & include it in commercial projects.
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Many language implementations either wrap libyaml or use it as inspiration.
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the big languages
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=================
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Let's start with the mainstream languages most developers use daily.
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**Python - PyYAML**
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License: MIT
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PyYAML is the standard YAML library for Python. Clean, permissive, widely used.
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**JavaScript - js-yaml & yaml**
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- js-yaml: MIT
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- yaml (by eemeli): ISC
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JavaScript has two popular options. Both use permissive licenses. ISC is functionally identical to MIT.
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**Java - SnakeYAML**
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License: Apache 2.0 (with some files under EPL-1.0, LGPL-2.1, GPL-2, or BSD)
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SnakeYAML uses Apache 2.0 for most code. Some included files carry different licenses for historical reasons.
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**Ruby - Psych**
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License: MIT
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Psych wraps libyaml for Ruby. Standard library inclusion. MIT licensed.
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**Go - go-yaml/yaml**
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License: MIT & Apache 2.0 (dual)
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Files ported from libyaml use MIT. New Go code uses Apache 2.0. You get both.
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**C/C++ - libyaml & yaml-cpp**
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- libyaml: MIT
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- yaml-cpp: MIT
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Both the canonical C library & the popular C++ alternative use MIT.
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the compiled languages
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======================
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**Rust - serde_yaml**
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License: MIT or Apache 2.0 (your choice)
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Rust's approach: dual licensing. Pick whichever license works for your project.
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**C# & VB.NET - YamlDotNet**
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License: MIT
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The .NET ecosystem uses YamlDotNet. Works with C#, VB.NET, F#, & other .NET languages.
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**Kotlin - kaml & hoplite**
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- kaml: Apache 2.0
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- hoplite: Apache 2.0
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Kotlin follows Java's lead with Apache licensing.
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**Scala - circe-yaml**
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License: Apache 2.0
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Scala's functional approach to YAML, Apache licensed.
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**Swift** (iOS/macOS)
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Most Swift YAML parsers wrap libyaml or use permissive licenses.
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the functional languages
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========================
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**Haskell - HsYAML**
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License: GPL-3.0
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**Plot twist!** HsYAML uses GPL-3.0, a copyleft license. This is rare in the YAML ecosystem.
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If you distribute software using HsYAML, you must release your source code under GPL-3.0 too.
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**F# - YamlDotNet**
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License: MIT
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F# uses the same YamlDotNet library as C#.
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**OCaml - ocaml-yaml**
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License: ISC
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OCaml's YAML library uses the permissive ISC license.
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**Elixir - yaml_elixir**
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Wraps Erlang's yamerl implementation.
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**Erlang - yamerl**
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License: BSD-2-Clause
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Pure Erlang YAML 1.2 parser. The 2-clause BSD license is extremely permissive.
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**Clojure - clj-yaml**
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License: EPL (Eclipse Public License)
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Clojure uses the same license as the language itself. EPL is a weak copyleft license.
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the scripting languages
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=======================
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**Perl**
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Multiple modules exist:
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- YAML, YAML::XS, YAML::Syck, YAML::Tiny, YAML::PP
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Most use Perl's standard licenses (Artistic License & GPL dual licensing).
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**PHP**
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- Symfony YAML Component: MIT
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- php-yaml (libyaml bindings): PHP License
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**Lua - lubyk/yaml**
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Based on libyaml, inherits its permissive licensing.
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**R - yaml**
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License: BSD-3-Clause
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R's YAML package wraps libyaml.
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**Bash/Shell - yq**
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Two implementations:
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- mikefarah/yq (Go): MIT
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- kislyuk/yq (Python wrapper): Apache 2.0
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yq brings YAML to shell scripts. Both implementations use permissive licenses.
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the systems languages
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=====================
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**Zig**
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YAML support is emerging. Most implementations use permissive licenses or are in early development.
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**Nim - NimYAML**
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License: MIT
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Nim's implementation follows the MIT pattern.
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**Crystal**
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License: Apache 2.0
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Crystal includes YAML in its standard library under Apache 2.0.
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**D - D:YAML**
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License: Boost Software License 1.0
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Boost is a permissive license designed for libraries.
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**V**
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YAML support is still emerging for this newer language.
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**Odin**
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Limited YAML library availability for this systems language.
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the niche languages
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===================
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**Fortran**
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Multiple implementations:
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- FYAML: MIT
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- fortran-yaml: GPL
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**Dart - yaml**
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License: MIT
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**Julia - YAML.jl**
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Open source, appears to follow Julia's standard MIT licensing.
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**Groovy**
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License: Apache 2.0
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Groovy's groovy-yaml ships with Apache 2.0.
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**Deno - yaml & @std/yaml**
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- deno.land/x/yaml: ISC
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- @std/yaml: MIT (Deno standard library)
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**PowerShell**
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- powershell-yaml: Apache 2.0
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- PSYaml: MIT
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Both wrap YamlDotNet underneath.
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**Tcl**
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YAML parser exists in tcllib.
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**Prolog - prolog-yamltiny**
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A YAML subset parser exists for Prolog.
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**Common Lisp - cl-yaml**
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License: MIT
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**Scheme**
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Limited YAML parsing library availability.
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**AWK**
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AWK isn't designed for YAML parsing. Use yq from shell scripts instead.
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**COBOL**
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No dedicated open-source YAML library found. COBOL applications typically use external tools or commercial solutions.
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**Mojo**
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Too new - YAML ecosystem still developing.
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This permissive license means you can use it anywhere, modify it freely, & include it in commercial projects. Many language implementations either wrap libyaml or use it as inspiration.
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the licenses
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============
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Here's the complete breakdown across 42+ programming languages:
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.. csv-table::
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:header: "Language", "Library/Implementation", "License", "Notes"
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:widths: 15, 20, 20, 45
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"**C**", "libyaml", "MIT", "Canonical implementation, foundation for many others"
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"**C++**", "yaml-cpp", "MIT", "Popular C++ alternative to libyaml"
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"**Python**", "PyYAML", "MIT", "Standard YAML library for Python"
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"**JavaScript**", "js-yaml", "MIT", "Most popular JS implementation"
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"**JavaScript**", "yaml (eemeli)", "ISC", "Modern alternative, functionally identical to MIT"
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"**Node.js**", "Same as JavaScript", "MIT/ISC", "Uses js-yaml or yaml package"
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"**Deno**", "deno.land/x/yaml", "ISC", "Third-party module"
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"**Deno**", "@std/yaml", "MIT", "Official Deno standard library"
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"**Java**", "SnakeYAML", "Apache 2.0", "Some files use EPL-1.0, LGPL-2.1, GPL-2, or BSD"
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"**Kotlin**", "kaml", "Apache 2.0", "Kotlin-specific implementation"
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"**Kotlin**", "hoplite", "Apache 2.0", "Configuration library with YAML support"
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"**Scala**", "circe-yaml", "Apache 2.0", "Functional approach to YAML"
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"**Groovy**", "groovy-yaml", "Apache 2.0", "Ships with Groovy"
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"**Clojure**", "clj-yaml", "EPL", "Eclipse Public License, weak copyleft"
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"**Ruby**", "Psych", "MIT", "Wraps libyaml, included in standard library"
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"**Go**", "go-yaml/yaml", "MIT & Apache 2.0", "Dual license: libyaml ports use MIT, new code uses Apache 2.0"
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"**Rust**", "serde_yaml", "MIT or Apache 2.0", "Dual license, pick either"
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"**C#**", "YamlDotNet", "MIT", "Works across .NET languages"
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"**VB.NET**", "YamlDotNet", "MIT", "Same library as C#"
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"**F#**", "YamlDotNet", "MIT", "Same library as C#"
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"**PowerShell**", "powershell-yaml", "Apache 2.0", "Wraps YamlDotNet"
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"**PowerShell**", "PSYaml", "MIT", "Alternative wrapper for YamlDotNet"
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"**Haskell**", "HsYAML", "GPL-3.0", "**Copyleft:** derivative works must use GPL-3.0"
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"**OCaml**", "ocaml-yaml", "ISC", "Permissive license"
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"**Elixir**", "yaml_elixir", "BSD-2-Clause", "Wraps Erlang's yamerl"
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"**Erlang**", "yamerl", "BSD-2-Clause", "Pure Erlang YAML 1.2 parser"
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"**Perl**", "YAML::XS, YAML::Syck, etc.", "Artistic & GPL", "Multiple modules, Perl's standard dual license"
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"**PHP**", "Symfony YAML", "MIT", "Part of Symfony framework"
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"**PHP**", "php-yaml", "PHP License", "libyaml bindings"
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"**Lua**", "lubyk/yaml", "MIT", "Based on libyaml"
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"**R**", "yaml", "BSD-3-Clause", "Wraps libyaml"
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"**Shell**", "yq (mikefarah)", "MIT", "Go-based YAML processor"
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"**Shell**", "yq (kislyuk)", "Apache 2.0", "Python-based wrapper"
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"**Bash**", "Use yq", "MIT/Apache 2.0", "Don't parse YAML with pure Bash"
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"**AWK**", "Use yq", "MIT/Apache 2.0", "AWK isn't designed for YAML parsing"
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"**Zig**", "Various", "Emerging", "Limited libraries, mostly permissive"
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"**Nim**", "NimYAML", "MIT", "Native Nim implementation"
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"**Crystal**", "Standard library", "Apache 2.0", "Built into language"
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"**D**", "D:YAML", "Boost 1.0", "Permissive license designed for libraries"
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"**V**", "Various", "Emerging", "Limited libraries available"
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"**Odin**", "Various", "Limited", "Few YAML libraries available"
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"**Swift**", "Various", "Mostly MIT", "Most wrap libyaml or use permissive licenses"
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"**Fortran**", "FYAML", "MIT", "Modern Fortran implementation"
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"**Fortran**", "fortran-yaml", "GPL", "Copyleft alternative"
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"**Dart**", "yaml", "MIT", "Standard Dart YAML package"
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"**Julia**", "YAML.jl", "MIT", "Follows Julia's standard licensing"
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"**Tcl**", "tcllib", "BSD-style", "Part of Tcl standard library"
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"**Prolog**", "prolog-yamltiny", "Various", "YAML subset parser"
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"**Common Lisp**", "cl-yaml", "MIT", "Standard CL implementation"
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"**Scheme**", "Various", "Limited", "Few YAML libraries available"
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"**COBOL**", "None found", "N/A", "Use external tools or commercial solutions"
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"**Mojo**", "None yet", "N/A", "Too new, ecosystem still developing"
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the pattern
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===========
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After reviewing 42+ languages, a clear pattern emerges:
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Looking at the table, three patterns emerge:
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**MIT & Apache 2.0 dominate.**
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**MIT & Apache 2.0 dominate the ecosystem.**
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These permissive licenses let you:
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- Use the code commercially
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- Modify it freely
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- Include it in proprietary software
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- Redistribute it
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Over 90% of implementations use permissive licenses. These let you use the code commercially, modify it freely, include it in proprietary software, & redistribute it without restrictions.
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**Copyleft licenses are rare.**
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**Copyleft is the exception, not the rule.**
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Only a few implementations use GPL or similar licenses:
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- Haskell's HsYAML (GPL-3.0)
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- Some Fortran parsers (GPL)
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- Clojure's EPL (weak copyleft)
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Only three implementations use copyleft licenses:
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- Haskell's HsYAML (GPL-3.0) - strong copyleft
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- Some Fortran parsers (GPL) - strong copyleft
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- Clojure's clj-yaml (EPL) - weak copyleft
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**Most wrap libyaml.**
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**libyaml's MIT license propagated through the ecosystem.**
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The C implementation serves as the foundation. Its MIT license propagates through the ecosystem.
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Many implementations wrap libyaml or port its code. The permissive MIT license enabled this reuse without legal friction.
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why it matters
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==============
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@ -336,16 +149,16 @@ When you ask "who owns YAML?" the answer is: the community. The spec is maintain
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That's the power of open standards & permissive licensing.
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special notes
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=============
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important notes
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===============
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**All licenses are valid choices.** We're proponents of all open source licenses - they each serve different purposes & communities. If you use HsYAML in Haskell or GPL-licensed Fortran parsers, you're choosing copyleft, which means derivative works inherit the GPL license. This ensures code freedom propagates. If you use MIT/Apache libraries, you're choosing permissive licensing, which maximizes reuse flexibility. Both approaches have merit.
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**All licenses are valid.** We're proponents of all open source licenses - they each serve different purposes. Copyleft (GPL, EPL) ensures derivative works remain open. Permissive licenses (MIT, Apache 2.0) maximize reuse flexibility. Both approaches have merit.
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**Java multi-licensing:** SnakeYAML's main license is Apache 2.0, but check the specific files if license compatibility matters for your project.
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**Check specific files.** SnakeYAML's main license is Apache 2.0, but some files use EPL-1.0, LGPL-2.1, GPL-2, or BSD for historical reasons. Review if license compatibility matters.
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**Emerging languages:** Zig, V, Mojo, & Odin have limited YAML libraries. Consider contributing if you need YAML support in these languages.
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**Shell scripting best practices.** Don't parse YAML with AWK, sed, or pure Bash. Use yq instead - it understands YAML's data structures & prevents parsing bugs.
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**Shell scripting:** Don't parse YAML with AWK or sed. Use yq - it understands the data structure & prevents bugs.
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**Emerging languages.** Zig, V, Mojo, & Odin have limited YAML ecosystem support. Consider contributing implementations if you need YAML in these languages.
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references
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==========
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