jyml

Zero-config YAML ↔ JSON converter. One command, no flags needed.

npx jyml config.yaml   # → config.json
npx jyml data.json      # → data.yaml

Why jyml

• Zero friction — pass a file, get the converted file. No flags required.
• Predictable — same filename, swapped extension, same directory.
• LLM-ready — --json structured output, documented exit codes, errors to stderr.
• Tiny — two dependencies, < 4 kB published.

Install

# Global install
npm install -g jyml

# Or run directly
npx jyml config.yaml

Usage

jyml <file> [options]

Arguments

| Argument | Description | |----------|-------------| | file | Path to the input file (.yaml, .yml, or .json) |

Options

| Option | Description | Default | |--------|-------------|---------| | -o, --output <path> | 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 | — |

Examples

# Convert an OpenAPI spec to JSON for code generators
jyml openapi.yaml
# → writes openapi.json

# Convert ESLint config from JSON to YAML
jyml .eslintrc.json
# → writes .eslintrc.yaml

# Grab a value from a GitHub Actions workflow in a script
jyml .github/workflows/ci.yml --json | jq '.content.jobs'

# Convert docker-compose for a tool that needs JSON
jyml docker-compose.yml -o docker-compose.json

# Convert a JSON API response to readable YAML with wider indent
jyml response.json --indent 4

I/O contract

| Stream | Content | |--------|---------| | stdout | Converted file content (only with --json) | | stderr | Progress messages, errors, diagnostics | | file | Converted output (default mode) |

--json output schema

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

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

License

MIT