🥨 Yaml::Converter

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Transform annotated YAML blueprints into human-friendly documentation. This gem:

• Fences raw YAML content
• Injects a validation status line with date (deterministic via current_date option)
• Extracts inline #note: annotations into readable blockquotes (or PDF note sections)
• Truncates overly long YAML lines (configurable)
• Emits Markdown, HTML, PDF (native Prawn), DOCX/PDF/other via pandoc

Ideal for design documents stored as YAML, making them consumable in multiple formats.

Alternatives (none in Ruby, send a PR if you know of one):

• yaml2rst (Python, GPLv3+)
• yaml2doc (Python, GPLv3)

Tokens to Remember
Works with JRuby
Works with Truffle Ruby
Works with MRI Ruby 3
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Maintainer 🎖️
... 💖	🧊 🐙 🛖 🧪

Compatible with MRI Ruby 3.2.0+, and concordant releases of JRuby, and TruffleRuby.

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🧪 galtzo-floss/yaml-converter on GitLab	The Truth	💚	💚	💚	🐭 Tiny Matrix	➖
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🎮️ Discord Server		Let's	talk	about	this	library!

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Alternatively:

Install the gem and add to the application's Gemfile by executing:

bundle add yaml-converter

If bundler is not being used to manage dependencies, install the gem by executing:

gem install yaml-converter

This gem is cryptographically signed, and has verifiable SHA-256 and SHA-512 checksums by stone_checksums. Be sure the gem you install hasn’t been tampered with by following the instructions below.

Add my public key (if you haven’t already, expires 2045-04-29) as a trusted certificate:

gem cert --add <(curl -Ls https://raw.github.com/galtzo-floss/certs/main/pboling.pem)

You only need to do that once. Then proceed to install with:

gem install yaml-converter -P HighSecurity

The HighSecurity trust profile will verify signed gems, and not allow the installation of unsigned dependencies.

If you want to up your security game full-time:

bundle config set --global trust-policy MediumSecurity

MediumSecurity instead of HighSecurity is necessary if not all the gems you use are signed.

NOTE: Be prepared to track down certs for signed gems and add them the same way you added mine.

Pass options via API, CLI flags, or ENV variables.

Core Options:

• max_line_length (Integer, default 70)
• truncate (Boolean, default true)
• margin_notes (:auto | :inline | :ignore)
• validate (Boolean, default true)
• use_pandoc (Boolean, default false)
• pandoc_args (Array default ["-N", "--toc"])
• current_date (Date, default Date.today) for deterministic validation line
• pdf_page_size (e.g., LETTER)
• pdf_two_column_notes (Boolean)
• emit_footer (Boolean, default true)

ENV overrides (examples):

export YAML_CONVERTER_MAX_LINE_LEN=120
export YAML_CONVERTER_TRUNCATE=false
export YAML_CONVERTER_VALIDATE=false

Overwrite Warning: If the output file exists an informational warning is printed: "Overwriting existing file". Suppress by setting KETTLE_TEST_SILENT=true (used in CI/tests).

Deterministic Dates: Inject current_date: in options or stub time for tests; the state machine uses this value.

• Markdown (.md)
• HTML (.html) via kramdown
• PDF (.pdf) native (Prawn) or via pandoc when use_pandoc: true
• DOCX (.docx) via pandoc (auto-detects pandoc path)
• Other pandoc-supported formats (set output extension + --use-pandoc)

Inline #note: at end of a YAML line:

key: value #note: important detail

Will produce a blockquote note just after the YAML fenced block.

Override defaults using ENV (before process start):

export YAML_CONVERTER_MAX_LINE_LEN=120
export YAML_CONVERTER_TRUNCATE=false
export YAML_CONVERTER_VALIDATE=false

Any comment line that begins with # YAML validation: will be replaced with a status and date:

YAML validation:*OK* on dd/mm/YYYY

----
Produced by yaml-converter

The above production footer is appended by default. Disable via ENV:

export YAML_CONVERTER_EMIT_FOOTER=false

Or per-call:

Yaml::Converter.to_markdown(yaml_str, options: {emit_footer: false})

For very large YAML files, enable streaming to keep memory usage low. Streaming processes the input line-by-line and writes Markdown incrementally while preserving identical output to non-streaming mode.

How it works:

• Same parsing and state machine logic as non-streaming
• Injects validation status if validate is enabled
• Closes YAML fences correctly even at EOF
• Appends standard footer when enabled

When streaming is used:

• Streaming is applied only to direct .md outputs. Other formats still render via an intermediate Markdown string.
• The output is intended to be byte-for-byte equivalent to the non-streaming path (see tests).

Quick start (API):

require "yaml/converter"

# Force streaming regardless of file size
Yaml::Converter.convert(
  input_path: "big.yaml",
  output_path: "big.md",
  options: {streaming: true, validate: true},
)

# Auto-stream based on file size threshold (bytes)
Yaml::Converter.convert(
  input_path: "maybe_big.yaml",
  output_path: "maybe_big.md",
  options: {streaming_threshold_bytes: 10_000_000}, # 10 MB (default is 5 MB)
)

Quick start (CLI):

# Force streaming for markdown output
yaml-convert big.yaml big.md --streaming

# Auto-stream for inputs >= 10MB
yaml-convert big.yaml big.md --streaming-threshold 10000000

# Batch + streaming to .md
yaml-convert \
  --glob 'docs/**/*.yaml' \
  --out-ext md \
  --out-dir out/ \
  --streaming

Environment variables:

# Enable streaming globally
export YAML_CONVERTER_STREAMING=1

# Default size threshold for auto streaming (bytes)
export YAML_CONVERTER_STREAMING_THRESHOLD_BYTES=5000000   # 5 MB default

Advanced: custom IO target (pure streaming):

If you want to stream directly to any IO (file/socket/StringIO), use the low-level streaming API:

require "yaml/converter"

File.open("big.md", "w") do |io|
  Yaml::Converter.to_markdown_streaming(
    "big.yaml",
    io,
    options: {validate: true}, # same options as non-streaming
  )
end

Notes:

• For .html, .pdf, .docx (and other pandoc-driven formats), the implementation first produces a full Markdown string, so streaming is not applied to those outputs.
• If the destination file already exists, you’ll see: "Overwriting existing file" (suppress with KETTLE_TEST_SILENT=true).

Minimal conversion to Markdown:

require "yaml/converter"
markdown = Yaml::Converter.to_markdown(File.read("spec/fixtures/example.yaml"))
puts markdown

Convert directly to a file (extension decides behavior):

Yaml::Converter.convert(
  input_path: "spec/fixtures/example.yaml",
  output_path: "doc/example.html",
  options: {validate: true},
)

Deterministic date for tests (inject current_date):

Yaml::Converter.to_markdown(yaml_str, options: {current_date: Date.new(2025, 11, 8)})

Native PDF vs pandoc PDF:

# Native PDF using Prawn
Yaml::Converter.convert(
  input_path: "blueprint.yaml",
  output_path: "blueprint.pdf",
  options: {use_pandoc: false, pdf_two_column_notes: true},
)

# PDF via pandoc (requires pandoc in PATH)
Yaml::Converter.convert(
  input_path: "blueprint.yaml",
  output_path: "blueprint.pdf",
  options: {use_pandoc: true, pandoc_args: ["-N", "--toc"]},
)

DOCX via pandoc:

Yaml::Converter.convert(
  input_path: "blueprint.yaml",
  output_path: "blueprint.docx",
  options: {},
)

Install gem (development checkout already has exe script):

yaml-convert input.yaml output.md
yaml-convert input.yaml output.html
yaml-convert input.yaml output.pdf --use-pandoc

If pandoc is not installed, the command will exit with code 5 and a helpful message.

DOCX example (CLI):

yaml-convert blueprint.yaml output.docx --use-pandoc

Batch mode with glob:

yaml-convert --glob 'docs/**/*.yaml' --out-ext md --out-dir out/

While galtzo-floss tools are free software and will always be, the project would benefit immensely from some funding. Raising a monthly budget of... "dollars" would make the project more sustainable.

We welcome both individual and corporate sponsors! We also offer a wide array of funding channels to account for your preferences (although currently Open Collective is our preferred funding platform).

If you're working in a company that's making significant use of galtzo-floss tools we'd appreciate it if you suggest to your company to become a galtzo-floss sponsor.

You can support the development of galtzo-floss tools via GitHub Sponsors, Liberapay, PayPal, Open Collective and Tidelift.

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I’m driven by a passion to foster a thriving open-source community – a space where people can tackle complex problems, no matter how small. Revitalizing libraries that have fallen into disrepair, and building new libraries focused on solving real-world challenges, are my passions. I was recently affected by layoffs, and the tech jobs market is unwelcoming. I’m reaching out here because your support would significantly aid my efforts to provide for my family, and my farm (11 🐔 chickens, 2 🐶 dogs, 3 🐰 rabbits, 8 🐈‍ cats).

If you work at a company that uses my work, please encourage them to support me as a corporate sponsor. My work on gems you use might show up in bundle fund.

I’m developing a new library, floss_funding, designed to empower open-source developers like myself to get paid for the work we do, in a sustainable way. Please give it a look.

Floss-Funding.dev: 👉️ No network calls. 👉️ No tracking. 👉️ No oversight. 👉️ Minimal crypto hashing. 💡 Easily disabled nags

See SECURITY.md.

If you need some ideas of where to help, you could work on adding more code coverage, or if it is already 💯 (see below) check reek, issues, or PRs, or use the gem and think about how it could be better.

We so if you make changes, remember to update it.

See CONTRIBUTING.md for more detailed instructions.

See CONTRIBUTING.md.

Everyone interacting with this project's codebases, issue trackers, chat rooms and mailing lists agrees to follow the .

Made with contributors-img.

Also see GitLab Contributors: https://gitlab.com/galtzo-floss/yaml-converter/-/graphs/main

This Library adheres to . Violations of this scheme should be reported as bugs. Specifically, if a minor or patch version is released that breaks backward compatibility, a new version should be immediately released that restores compatibility. Breaking changes to the public API will only be introduced with new major versions.

dropping support for a platform is both obviously and objectively a breaking change
—Jordan Harband (@ljharb, maintainer of SemVer) in SemVer issue 716

I understand that policy doesn't work universally ("exceptions to every rule!"), but it is the policy here. As such, in many cases it is good to specify a dependency on this library using the Pessimistic Version Constraint with two digits of precision.

For example:

spec.add_dependency("yaml-converter", "~> 0.1")

SemVer should, IMO, but doesn't explicitly, say that dropping support for specific Platforms is a breaking change to an API, and for that reason the bike shedding is endless.

To get a better understanding of how SemVer is intended to work over a project's lifetime, read this article from the creator of SemVer:

• "Major Version Numbers are Not Sacred"

See CHANGELOG.md for a list of releases.

The gem is available as open source under the terms of the MIT License . See LICENSE.txt for the official Copyright Notice.

• Copyright (c) 2025 Peter H. Boling, of Galtzo.com , and yaml-converter contributors.

Maintainers have teeth and need to pay their dentists. After getting laid off in an RIF in March, and encountering difficulty finding a new one, I began spending most of my time building open source tools. I'm hoping to be able to pay for my kids' health insurance this month, so if you value the work I am doing, I need your support. Please consider sponsoring me or the project.

To join the community or get help 👇️ Join the Discord.

To say "thanks!" ☝️ Join the Discord or 👇️ send money.

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Thanks for RTFM. ☺️