jt - JSONata Query Tool

jt is a powerful command-line tool for querying and transforming JSON data using JSONata, a lightweight query and transformation language for JSON.

Features

• 🔍 Query JSON, YAML, CSV, and JSON Lines data using JSONata expressions
• 🔄 Format conversion between JSON, YAML, JSON Lines, and CSV (no query required)
• 📝 Multiple output formats: JSON (with compact option), JSON Lines, YAML, and CSV
• 🚀 Fast and efficient processing with streaming support
• 💡 User-friendly error messages with helpful suggestions
• 📖 Support for both stdin and file input
• 🎯 TypeScript implementation with full type safety

Installation

Using npm

npm install -g @2017takeda/jt-cli

Using Homebrew (coming soon)

brew install jt

Usage

Basic Usage

# Query from file
jt '<jsonata-expression>' input.json

# Query from stdin
cat data.json | jt '<jsonata-expression>'

# With explicit input format
jt -i yaml '<jsonata-expression>' data.yaml

# Format conversion without JSONata query (new!)
jt data.json -o yaml
cat data.yaml | jt -c

The JSONata expression is now optional. When omitted, jt acts as a format converter, parsing the input and outputting it in the specified format.

Examples

Format Conversion (No Query)

# Convert JSON to YAML
jt data.json -o yaml

# Convert YAML to JSON
jt config.yaml -o json

# Convert JSON to compact format
cat data.json | jt -c

# Convert JSON Lines to YAML
jt events.jsonl -o yaml

Basic Query

# Extract all names from an array of objects
echo '[{"name": "Alice", "age": 30}, {"name": "Bob", "age": 25}]' | jt '$.name'
# Output: ["Alice", "Bob"]

Filtering

# Filter objects where age > 25
echo '[{"name": "Alice", "age": 30}, {"name": "Bob", "age": 25}]' | jt '$[age > 25]'
# Output: [{"name": "Alice", "age": 30}]

Transformation

# Transform data structure
echo '{"users": [{"first": "John", "last": "Doe"}]}' | jt 'users.{"fullName": first & " " & last}'
# Output: [{"fullName": "John Doe"}]

Aggregation

# Sum all values
echo '[{"value": 10}, {"value": 20}, {"value": 30}]' | jt '$sum(value)'
# Output: 60

Input Formats

jt supports multiple input formats:

• JSON (default): Standard JSON format
• YAML: YAML format (-i yaml or --input yaml)
• JSON Lines: Newline-delimited JSON (-i jsonl or --input jsonl)
• CSV: Comma-separated values with headers (-i csv or --input csv)

# YAML input
jt -i yaml '$.users.name' config.yaml

# JSON Lines input
jt -i jsonl '$.event' events.jsonl

# CSV input
jt -i csv '$[age > 25]' users.csv

Output Formats

Control output formatting with the -o or --output option:

• json (default): Formatted JSON with indentation
  • Use -c or --compact flag for minified JSON
• jsonl: JSON Lines (one JSON per line)
• yaml: YAML format
• csv: CSV format (for tabular data)

# Compact JSON output
jt -c '$.users' data.json

# YAML output
jt -o yaml '$.config' settings.json

# CSV output (for arrays of objects)
jt -o csv '$' users.json

Raw String Output

Use the -r or --raw-string flag to output raw strings without quotes:

# Extract string value without quotes
echo '{"name": "Alice", "age": 30}' | jt -r '$.name'
# Output: Alice (instead of "Alice")

# Works with numbers and booleans too
echo '{"count": 42, "active": true}' | jt -r '$.count'
# Output: 42 (as string)

# Multiline strings are output with actual newlines
echo '{"text": "Line 1\nLine 2"}' | jt -r '$.text'
# Output:
# Line 1
# Line 2

# Arrays and objects are still output as JSON
echo '{"list": [1, 2, 3]}' | jt -r '$.list'
# Output: [1, 2, 3]

This option is useful for:

• Shell scripting where you need unquoted values
• Extracting text content without JSON formatting
• Similar to jq -r for those familiar with that tool

Advanced Features

Using JSONata Functions

# String manipulation
echo '{"name": "john doe"}' | jt '{"name": $uppercase(name)}'
# Output: {"name": "JOHN DOE"}

# Date handling
echo '{"date": "2023-12-01"}' | jt '{"year": $substring(date, 0, 4)}'
# Output: {"year": "2023"}

Complex Queries

# Group and aggregate
echo '[{"dept": "sales", "salary": 50000}, {"dept": "sales", "salary": 60000}]' | \
  jt 'dept{dept: $sum(salary)}'
# Output: {"sales": 110000}

JSONata Expression Language

JSONata is a powerful query language designed specifically for JSON. Key features include:

• Path expressions: $.users[0].name
• Filtering: $.users[age > 21]
• Mapping: $.users.{"fullName": firstName & " " & lastName}
• Aggregation: $sum($.items.price)
• Functions: $uppercase(), $substring(), $now(), etc.

For complete JSONata documentation, visit jsonata.org.

Error Handling

jt provides clear, actionable error messages:

# Invalid JSON input
echo '{invalid}' | jt '$'
# Error: Invalid JSON input at position 1: Unexpected token 'i'

# Invalid JSONata expression
echo '{}' | jt '$undefined('
# Error: Invalid JSONata expression: Unexpected token '(' at position 11

Development

Prerequisites

• Node.js 20 or higher (Node.js 24 recommended)
• npm or yarn
• nvm (recommended for managing Node.js versions)

Setup

# Clone repository
git clone https://github.com/TAKEDA-Takashi/jt-cli.git
cd jt-cli

# Use the recommended Node.js version (if using nvm)
nvm use  # This will use the version specified in .nvmrc (Node.js 24)

# Install dependencies
npm install

# Run tests
npm test

# Build
npm run build

Testing

This project follows Test-Driven Development (TDD) practices:

# Run all tests
npm test

# Run tests in watch mode
npm run test:watch

# Run with coverage
npm run test:coverage

Contributing

We welcome contributions! Please see our Contributing Guide for details.

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Write tests for your changes
4. Implement your changes
5. Ensure all tests pass
6. Commit your changes (git commit -m 'feat: add amazing feature')
7. Push to the branch (git push origin feature/amazing-feature)
8. Open a Pull Request

Code Ownership

This project uses CODEOWNERS to define responsibilities for different parts of the codebase. Code owners are automatically requested for review when pull requests modify files they own.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

• JSONata - The powerful JSON query language
• Commander.js - CLI framework
• Biome - Fast formatter and linter

Support

• 📝 Report issues
• 💬 Discussions
• 📖 Documentation