JSONata Validator Extension

A lightweight VS Code extension for validating JSONata templates without requiring a language server. This extension provides real-time validation of JSONata expressions using the official JSONata library.

Features

• Real-time validation: Validates JSONata expressions as you type
• Precise error reporting: Shows exact error positions with JSONata error codes (e.g., S0201, S0203)
• Detailed error messages: Includes expected vs. actual tokens for better debugging
• Multi-line expression support: Handles complex JSONata expressions spanning multiple lines
• Multiple file support: Works with .jsonata files and detects JSONata expressions in JSON files
• Context menu commands: Right-click to validate documents or selections
• Configurable: Customize validation behavior through VS Code settings
• Lightweight: No language server required - everything runs locally using the official JSONata library

Validation Features

The extension provides comprehensive JSONata validation by leveraging the official JSONata parser:

Error Detection

• Syntax errors: Invalid JSONata syntax with precise error locations
• Missing brackets/parentheses: Detects unclosed [, (, { with exact positions
• Invalid operators: Catches invalid operator usage like .. double dots
• Function call errors: Validates function syntax and parameter structure

Error Reporting

• Error codes: Shows JSONata error codes (S0201, S0203, etc.)
• Precise positioning: Highlights exact character where error occurs
• Helpful messages: "Expected ']', got '}'" style messages
• Token information: Shows actual vs. expected tokens

Expression Types Supported

• Simple property access: $.firstName
• Array filtering: $.products[price > 100]
• Complex transformations: $.orders[status = "shipped"].{name: customer, total: total}
• Function calls: $sum($.items.price)
• Multi-line expressions with proper bracket matching

Usage

File Types Supported

1. .jsonata files: Dedicated JSONata template files with full multi-line support
2. JSON files: Automatically detects JSONata expressions within JSON strings

Commands

• Validate JSONata Document: Validates the entire active document
• Validate JSONata Selection: Validates only the selected text

Access these commands via:

• Command Palette (Ctrl+Shift+P / Cmd+Shift+P)
• Right-click context menu (when editing .jsonata files)

Configuration

Configure the extension through VS Code settings:

{
  "jsonataValidator.validateOnType": true,        // Validate as you type
  "jsonataValidator.validateOnSave": true,        // Validate when saving
  "jsonataValidator.maxNumberOfProblems": 100     // Maximum errors to show
}

Examples

Valid JSONata Expressions

$.firstName
$.address.city
$.products[price > 100]
$.orders[status = "shipped"].total ~> $sum()

// Multi-line expressions
$.products[
  price > 100 and
  category = "electronics"
].{
  "name": name,
  "discountedPrice": price * 0.9
}

Error Examples with Improved Reporting

// Error S0201: Syntax error: ".."
$.firstName..invalid

// Error S0203: Expected "]" before end of expression
$.products[price > 100

// Error S0202: Expected ")", got "syntax"
$count(invalid syntax here

// Error S0203: Expected "}" before end of expression
$.{unclosed: "object"

The extension now shows:

• Error codes (S0201, S0203, etc.)
• Exact positions where errors occur
• Expected vs. actual tokens for clearer debugging

Development

To build and run the extension locally:

npm install
npm run compile

Press F5 in VS Code to launch the extension in a new Extension Development Host window.

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Test thoroughly
5. Submit a pull request

License

MIT License - see LICENSE file for details.