📍 NOTE
RubyGems (the GitHub org, not the website) suffered a hostile takeover in September 2025.
Ultimately 4 maintainers were hard removed and a reason has been given for only 1 of those, while 2 others resigned in protest.
It is a complicated story which is difficult to parse quickly.
Simply put - there was active policy for adding or removing maintainers/owners of rubygems and bundler, and those policies were not followed.
I'm adding notes like this to gems because I don't condone theft of repositories or gems from their rightful owners.
If a similar theft happened with my repos/gems, I'd hope some would stand up for me.
Disenfranchised former-maintainers have started gem.coop.
Once available I will publish there exclusively; unless RubyCentral makes amends with the community.
The "Technology for Humans: Joel Draper" podcast episode by reinteractive is the most cogent summary I'm aware of.
See here, here and here for more info on what comes next.
What I'm doing: A (WIP) proposal for bundler/gem scopes, and a (WIP) proposal for a federated gem server.

☯️ Json::Merge

if ci_badges.map(&:color).detect { it != "green"} ☝️ let me know, as I may have missed the discord notification.

---

if ci_badges.map(&:color).all? { it == "green"} 👇️ send money so I can do more of this. FLOSS maintenance is now my full-time job.

🌻 Synopsis

Json::Merge is a standalone Ruby module that intelligently merges two versions of a JSON file using tree-sitter AST analysis. It's like a smart "git merge" specifically designed for JSON configuration files. Built on top of ast-merge, it shares the same architecture as prism-merge for Ruby source files.

For JSONC (JSON with Comments) support, see the jsonc-merge gem.

Key Features

• Tree-Sitter Powered: Uses tree-sitter-json for accurate AST parsing
• Intelligent: Matches objects and arrays by structural signatures
• Fuzzy Property Matching: ObjectMatchRefiner matches similar property names (e.g., databaseUrl ↔ database_url) using Levenshtein distance for naming convention differences
• Full Provenance: Tracks origin of every node
• Standalone: Minimal dependencies - just ast-merge and ruby_tree_sitter
• Customizable:
  • signature_generator - callable custom signature generators
  • preference - setting of :template, :destination, or a Hash for per-node-type preferences
  • node_splitter - Hash mapping node types to callables for per-node-type merge customization (see ast-merge docs)
  • add_template_only_nodes - setting to retain nodes that do not exist in destination
  • match_refiners - array of refiners for fuzzy matching (e.g., ObjectMatchRefiner)

Supported Node Types

Node Type	Signature Format	Matching Behavior
Object	[:object, key_signatures...]	Objects match by their key structure
Array	[:array, element_count]	Arrays match by position and type
Pair	[:pair, key_name]	Key-value pairs match by key name
String	[:string, value]	Strings match by value
Number	[:number, value]	Numbers match by value
Boolean	[:boolean, value]	Booleans match by value
Null	[:null]	Null values always match

Example

require "json/merge"

template = File.read("template.json")
destination = File.read("destination.json")

merger = Json::Merge::SmartMerger.new(template, destination)
result = merger.merge

File.write("merged.json", result.to_json)

The *-merge Gem Family

The *-merge gem family provides intelligent, AST-based merging for various file formats. At the foundation is tree_haver, which provides a unified cross-Ruby parsing API that works seamlessly across MRI, JRuby, and TruffleRuby.

Gem	Language / Format	Parser Backend(s)	Description
tree_haver	Multi	MRI C, Rust, FFI, Java, Prism, Psych, Commonmarker, Markly, Citrus	Foundation: Cross-Ruby adapter for parsing libraries (like Faraday for HTTP)
ast-merge	Text	internal	Infrastructure: Shared base classes and merge logic for all *-merge gems
bash-merge	Bash	tree-sitter-bash (via tree_haver)	Smart merge for Bash scripts
commonmarker-merge	Markdown	Commonmarker (via tree_haver)	Smart merge for Markdown (CommonMark via comrak Rust)
dotenv-merge	Dotenv	internal	Smart merge for .env files
json-merge	JSON	tree-sitter-json (via tree_haver)	Smart merge for JSON files
jsonc-merge	JSONC	tree-sitter-jsonc (via tree_haver)	⚠️ Proof of concept; Smart merge for JSON with Comments
markdown-merge	Markdown	Commonmarker / Markly (via tree_haver)	Foundation: Shared base for Markdown mergers with inner code block merging
markly-merge	Markdown	Markly (via tree_haver)	Smart merge for Markdown (CommonMark via cmark-gfm C)
prism-merge	Ruby	Prism (prism std lib gem)	Smart merge for Ruby source files
psych-merge	YAML	Psych (psych std lib gem)	Smart merge for YAML files
rbs-merge	RBS	tree-sitter-bash (via tree_haver), RBS (rbs std lib gem)	Smart merge for Ruby type signatures
toml-merge	TOML	Citrus + toml-rb (default, via tree_haver), tree-sitter-toml (via tree_haver)	Smart merge for TOML files

Backend Platform Compatibility

tree_haver supports multiple parsing backends, but not all backends work on all Ruby platforms:

Platform 👉️ TreeHaver Backend 👇️	MRI	JRuby	TruffleRuby	Notes
MRI (ruby_tree_sitter)	✅	❌	❌	C extension, MRI only
Rust (tree_stump)	✅	❌	❌	Rust extension via magnus/rb-sys, MRI only
FFI	✅	✅	❌	TruffleRuby's FFI doesn't support STRUCT_BY_VALUE
Java (jtreesitter)	❌	✅	❌	JRuby only, requires grammar JARs
Prism	✅	✅	✅	Ruby parsing, stdlib in Ruby 3.4+
Psych	✅	✅	✅	YAML parsing, stdlib
Citrus	✅	✅	✅	Pure Ruby, no native dependencies
Commonmarker	✅	❌	❓	Rust extension for Markdown
Markly	✅	❌	❓	C extension for Markdown

Legend: ✅ = Works, ❌ = Does not work, ❓ = Untested

Why some backends don't work on certain platforms:

• JRuby: Runs on the JVM; cannot load native C/Rust extensions (.so files)
• TruffleRuby: Has C API emulation via Sulong/LLVM, but it doesn't expose all MRI internals that native extensions require (e.g., RBasic.flags, rb_gc_writebarrier)
• FFI on TruffleRuby: TruffleRuby's FFI implementation doesn't support returning structs by value, which tree-sitter's C API requires

Example implementations for the gem templating use case:

Gem	Purpose	Description
kettle-dev	Gem Development	Gem templating tool using *-merge gems
kettle-jem	Gem Templating	Gem template library with smart merge support

💡 Info you can shake a stick at

Tokens to Remember
Works with JRuby
Works with Truffle Ruby
Works with MRI Ruby 3
Support & Community
Source
Documentation
Compliance
Style
Maintainer 🎖️
... 💖	🧊 🐙 🛖 🧪

Compatibility

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

🚚 Amazing test matrix was brought to you by	🔎 appraisal2 🔎 and the color 💚 green 💚
👟 Check it out!	✨ github.com/appraisal-rb/appraisal2 ✨

Federated DVCS

Find this repo on federated forges (Coming soon!)

Federated DVCS Repository	Status	Issues	PRs	Wiki	CI	Discussions
🧪 kettle-rb/json-merge on GitLab	The Truth	💚	💚	💚	🐭 Tiny Matrix	➖
🧊 kettle-rb/json-merge on CodeBerg	An Ethical Mirror (Donate)	💚	💚	➖	⭕️ No Matrix	➖
🐙 kettle-rb/json-merge on GitHub	Another Mirror	💚	💚	💚	💯 Full Matrix	💚
🎮️ Discord Server		Let's	talk	about	this	library!

Enterprise Support

Available as part of the Tidelift Subscription.

Need enterprise-level guarantees?

The maintainers of this and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source packages you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact packages you use.

• 💡Subscribe for support guarantees covering all your FLOSS dependencies

• 💡Tidelift is part of Sonar

• 💡Tidelift pays maintainers to maintain the software you depend on!
  📊@Pointy Haired Boss: An enterprise support subscription is "never gonna let you down", and supports open source maintainers Alternatively:

• 

• 

• 

✨ Installation

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

bundle add json-merge

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

gem install json-merge

🔒 Secure Installation

For Medium or High Security Installations

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 json-merge -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.

🌳 Tree-Sitter Parser Installation

This gem requires the tree-sitter-json parser library to be installed on your system. The parser is a native shared library (.so on Linux, .dylib on macOS) that provides JSON syntax parsing capabilities. For JSONC (JSON with Comments) support, use the jsonc-merge gem instead.

Option 1: Pre-built Binaries (Recommended)

Download pre-built parsers from Faveod/tree-sitter-parsers:

Linux (x64):

# Download and extract
curl -Lo parsers.tar.gz https://github.com/Faveod/tree-sitter-parsers/releases/download/v4.10/tree-sitter-parsers-4.10-linux-x64.tar.gz
tar -xzf parsers.tar.gz

# Install system-wide (requires sudo)
sudo cp libtree-sitter-json.so /usr/lib/
sudo ldconfig

# Or install locally and set environment variable
mkdir -p ~/.local/lib/tree-sitter
cp libtree-sitter-json.so ~/.local/lib/tree-sitter/
export TREE_SITTER_JSON_PATH="$HOME/.local/lib/tree-sitter/libtree-sitter-json.so"

Debian/Ubuntu (amd64):

curl -Lo parsers.deb https://github.com/Faveod/tree-sitter-parsers/releases/download/v4.10/tree-sitter-parsers-4.10-amd64.deb
sudo dpkg -i parsers.deb

macOS (Apple Silicon):

curl -Lo parsers.tar.gz https://github.com/Faveod/tree-sitter-parsers/releases/download/v4.10/tree-sitter-parsers-4.10-macos-arm64.tar.gz
tar -xzf parsers.tar.gz

# Install to a location and set environment variable
mkdir -p ~/.local/lib/tree-sitter
cp libtree-sitter-json.dylib ~/.local/lib/tree-sitter/
export TREE_SITTER_JSON_PATH="$HOME/.local/lib/tree-sitter/libtree-sitter-json.dylib"

Option 2: Build from Source

git clone https://github.com/tree-sitter/tree-sitter-json.git
cd tree-sitter-json
make
sudo cp libtree-sitter-json.so /usr/lib/  # Linux
# or
sudo cp libtree-sitter-json.dylib /usr/local/lib/  # macOS

Option 3: Package Manager

Some package managers provide tree-sitter parsers:

Fedora Atomic (Silverblue, Kinoite, Bazzite, Aurora, etc.):

# Install via rpm-ostree (requires reboot)
rpm-ostree install libtree-sitter-json

# The library will be installed to /usr/lib64/libtree-sitter-json.so
# You may need to set the environment variable:
export TREE_SITTER_JSON_PATH="/usr/lib64/libtree-sitter-json.so"

Fedora (traditional):

sudo dnf install libtree-sitter-json

Arch Linux:

# Check AUR for tree-sitter-json
yay -S tree-sitter-json

Environment Variable

If the parser is not in a standard location (/usr/lib/, /usr/lib64/, /usr/local/lib/), set the TREE_SITTER_JSON_PATH environment variable to point to the parser library:

export TREE_SITTER_JSON_PATH="/path/to/libtree-sitter-json.so"

Note: Some distributions install the library with a version number suffix (e.g., libtree-sitter-json.so.14 instead of libtree-sitter-json.so). If the gem can't find the parser, check for versioned files and either:

• Set TREE_SITTER_JSON_PATH to the full versioned path, or
• Create a symlink: sudo ln -s /usr/lib64/libtree-sitter-json.so.14 /usr/lib64/libtree-sitter-json.so Add this to your shell profile (.bashrc, .zshrc, etc.) for persistence.

💎 Ruby Interface Gems

In addition to the tree-sitter parser library, you need a Ruby gem that provides bindings to tree-sitter. Choose one of the following based on your Ruby implementation:

Gem	Ruby Support	Description
ruby_tree_sitter	MRI only	C extension bindings (recommended for MRI)
tree_stump	MRI (maybe JRuby)	Rust-based bindings via Rutie
ffi	MRI, JRuby, TruffleRuby	Generic FFI bindings (used by tree_haver's FFI backend)

For MRI Ruby (Recommended)

gem install ruby_tree_sitter

Or add to your Gemfile:

gem "ruby_tree_sitter", "~> 2.0"

For JRuby or TruffleRuby

gem install ffi

Or add to your Gemfile:

gem "ffi"

The tree_haver gem (a dependency of json-merge) will automatically detect and use the appropriate backend based on which gems are available.

Note: The ruby_tree_sitter gem only compiles on MRI Ruby. For JRuby or TruffleRuby, you must use the FFI backend.

⚙️ Configuration

Signature Match Preference

Control which version to use when nodes have matching signatures but different content:

# Use template version (for config updates)
merger = Json::Merge::SmartMerger.new(
  template,
  destination,
  preference: :template,
)

# Use destination version (default - preserve customizations)
merger = Json::Merge::SmartMerger.new(
  template,
  destination,
  preference: :destination,
)

Template-Only Nodes

Control whether to add nodes that only exist in the template:

# Add template-only nodes
merger = Json::Merge::SmartMerger.new(
  template,
  destination,
  add_template_only_nodes: true,
)

Object Match Refiner

When JSON object properties (key-value pairs) don't match by exact key name, the ObjectMatchRefiner uses fuzzy matching to pair entries with:

• Similar key names (e.g., databaseUrl vs database_url)
• Keys with typos or different naming conventions (camelCase vs snake_case)
• Array elements with similar structure or content

# Enable object fuzzy matching
merger = Json::Merge::SmartMerger.new(
  template,
  destination,
  match_refiners: [
    Json::Merge::ObjectMatchRefiner.new(threshold: 0.5),
  ],
)

ObjectMatchRefiner Options

Option	Default	Description
threshold	0.5	Minimum similarity score (0.0-1.0) to accept a match
key_weight	0.7	Weight for key name similarity
value_weight	0.3	Weight for value similarity

# Custom weights for key-centric matching
refiner = Json::Merge::ObjectMatchRefiner.new(
  threshold: 0.6,
  key_weight: 0.8,   # Focus more on key names
  value_weight: 0.2,  # Less focus on values
)

Debug Logging

Enable debug logging to see merge decisions:

export JSON_MERGE_DEBUG=1

🔧 Basic Usage

Merging Two JSON Files

require "json/merge"

template_content = File.read("template.json")
dest_content = File.read("destination.json")

merger = Json::Merge::SmartMerger.new(template_content, dest_content)
result = merger.merge

File.write("merged.json", result.to_json)

Analyzing a JSON File

require "json/merge"

source = File.read("config.json")
analysis = Json::Merge::FileAnalysis.new(source)

# Iterate over all top-level nodes
analysis.statements.each do |node|
  sig = analysis.generate_signature(node)
  puts "#{node.class}: #{sig.inspect}"
end

Fuzzy Property Matching

When property names differ between template and destination (e.g., naming convention changes), use the ObjectMatchRefiner:

require "json/merge"

template = <<~JSON
  {
    "databaseUrl": "postgres://localhost/app",
    "cacheTimeout": 3600,
    "apiEndpoint": "https://api.example.com"
  }
JSON

destination = <<~JSON
  {
    "database_url": "postgres://localhost/custom",
    "cache_ttl": 7200,
    "api_endpoint": "https://custom.example.com"
  }
JSON

# Default merge won't match keys (names differ - camelCase vs snake_case)
# Use ObjectMatchRefiner for fuzzy matching
merger = Json::Merge::SmartMerger.new(
  template,
  destination,
  match_refiners: [
    Json::Merge::ObjectMatchRefiner.new(threshold: 0.5),
  ],
)
result = merger.merge

# Properties are matched despite naming convention differences:
# - databaseUrl ↔ database_url (similar when normalized)
# - cacheTimeout ↔ cache_ttl (similar: "cache")
# - apiEndpoint ↔ api_endpoint (similar when normalized)

Array Element Matching

The ObjectMatchRefiner also handles array elements with similar structure:

template = <<~JSON
  {
    "users": [
      { "id": 1, "userName": "alice" },
      { "id": 2, "userName": "bob" }
    ]
  }
JSON

destination = <<~JSON
  {
    "users": [
      { "id": 1, "user_name": "alice_custom" },
      { "id": 3, "user_name": "charlie" }
    ]
  }
JSON

merger = Json::Merge::SmartMerger.new(
  template,
  destination,
  match_refiners: [
    Json::Merge::ObjectMatchRefiner.new(threshold: 0.5),
  ],
)
# Array elements with matching IDs or similar structure are paired

🦷 FLOSS Funding

While kettle-rb 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 kettle-rb tools we'd appreciate it if you suggest to your company to become a kettle-rb sponsor.

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

📍 NOTE
If doing a sponsorship in the form of donation is problematic for your company from an accounting standpoint, we'd recommend the use of Tidelift, where you can get a support-like subscription instead.

Open Collective for Individuals

Support us with a monthly donation and help us continue our activities. [Become a backer]

NOTE: kettle-readme-backers updates this list every day, automatically.

No backers yet. Be the first!

Open Collective for Organizations

Become a sponsor and get your logo on our README on GitHub with a link to your site. [Become a sponsor]

NOTE: kettle-readme-backers updates this list every day, automatically.

No sponsors yet. Be the first!

Another way to support open-source

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

🔐 Security

See SECURITY.md.

🤝 Contributing

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.

🚀 Release Instructions

See CONTRIBUTING.md.

Code Coverage

🪇 Code of Conduct

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

🌈 Contributors

Made with contributors-img.

Also see GitLab Contributors: https://gitlab.com/kettle-rb/json-merge/-/graphs/main

⭐️ Star History

📌 Versioning

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("json-merge", "~> 1.0")

📌 Is "Platform Support" part of the public API? More details inside.

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.

📄 License

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

© Copyright

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

🤑 A request for help

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.

💌 💌 💌

Please give the project a star ⭐ ♥.

Thanks for RTFM. ☺️