jyml

This skill should be used when the user asks to "convert YAML to JSON", "convert JSON to YAML", "transform YAML file", "transform JSON file", "convert config file format", or needs to switch between YAML and JSON formats.

jyml - YAML ↔ JSON Converter

Zero-config CLI for converting between YAML and JSON formats. Pass a file, get the converted file. No flags required.

Prerequisites

Ensure jyml is available:

# Check if installed
which jyml

# Install globally if needed
npm install -g jyml

# Or use npx for one-off conversions
npx jyml <file>

Requires Node.js 18 or later.

Basic Usage

jyml <file> [options]

The CLI auto-detects the input format based on file extension and converts to the opposite format:

Input Extension	Output Extension
.yaml, .yml	.json
.json	.yaml

Output is written to the same directory with the swapped extension.

Options

Option	Description	Default
-o, --output <path>	Custom output file path	Input file with swapped extension
--json	Print structured JSON to stdout (no file written)	—
--indent <n>	Indentation spaces	2
-h, --help	Show help	—
-V, --version	Show version	—

Common Workflows

Convert a single file

# YAML to JSON
jyml config.yaml
# → writes config.json

# JSON to YAML
jyml settings.json
# → writes settings.yaml

Convert with custom output path

jyml docker-compose.yml -o ./output/docker-compose.json

Convert with custom indentation

jyml response.json --indent 4

Extract data programmatically

Use --json to get structured output for piping to other tools:

# Get parsed content
jyml workflow.yml --json | jq '.content'

# Extract specific values
jyml .github/workflows/ci.yml --json | jq '.content.jobs'

Batch conversion

Convert multiple files using shell patterns:

# Convert all YAML files in a directory
for f in configs/*.yaml; do jyml "$f"; done

# Convert all JSON files
for f in data/*.json; do jyml "$f"; done

Output Modes

Default mode (file output)

Writes converted content to a file, prints progress to stderr:

jyml config.yaml
# stderr: Converting config.yaml → config.json
# Creates: config.json

Structured mode (--json)

Prints structured JSON to stdout, no file written:

{
  "input": "/path/to/input.yaml",
  "format": "json",
  "output": "/path/to/input.json",
  "content": { ... }
}

Field	Type	Description
input	string	Absolute path to the source file
format	string	Output format: "json" or "yaml"
output	string	Path where the file would be written
content	object	The parsed and converted data

Exit Codes

Code	Meaning
0	Success
1	Conversion error (invalid YAML/JSON, I/O failure)
2	Invalid usage (missing file, bad arguments, unsupported extension)

Error Handling

Errors are printed to stderr with actionable context:

Error: File not found: config.yaml
Error: Unsupported file extension ".txt". Supported: .yaml, .yml, .json
Error: Invalid YAML: bad indentation of a mapping entry (1:11)
Error: Invalid JSON: Expected property name or '}' in JSON at position 2

When conversion fails, check:

1. File exists and is readable
2. File extension is .yaml, .yml, or .json
3. File contains valid YAML or JSON syntax

Use Cases

OpenAPI/Swagger specs

Convert specs between formats for different tools:

# Convert OpenAPI spec to JSON for code generators
jyml openapi.yaml

# Convert back to YAML for documentation
jyml openapi.json

Configuration files

Switch config formats based on tool requirements:

# ESLint config to YAML
jyml .eslintrc.json

# Docker Compose to JSON
jyml docker-compose.yml

GitHub Actions workflows

Parse workflow files for scripting:

# Extract job names from a workflow
jyml .github/workflows/ci.yml --json | jq '.content.jobs | keys'

API response inspection

Convert JSON responses to readable YAML:

curl -s https://api.example.com/data > response.json
jyml response.json --indent 4
cat response.yaml