JSON5 validator for syntax and format checks
JSON5 Validator checks JSON5 documents for proper syntax, comment formatting, trailing comma support, and structural compliance. Paste code, review line-by-line errors, and fix issues before deployment. Everything runs in the browser so your data stays private.
JSON5 validation process
Code input
Paste JSON5 code into the editor. The validator accepts single-line comments, multi-line comments, trailing commas, and unquoted keys.
Comment removal
Single-line comments starting with // and multi-line comments between are stripped before parsing. Nested comments trigger errors.
Structure analysis
The parser checks bracket matching, brace pairing, string closure, and trailing comma placement. Property names validate against JSON5 rules.
Error reporting
Validation results display with line numbers and error types. Valid JSON5 shows a success message. Invalid code lists specific issues to fix.
Common JSON5 validation errors
Syntax Errors
Unclosed brackets, mismatched braces, invalid characters
Comment Issues
Nested comments, unclosed comment blocks, invalid comment syntax
Structure Issues
Improper nesting, missing commas, invalid property names
Quote Problems
Unclosed strings, mismatched quotes, invalid escape sequences
Real-world validation scenarios
Config file validation before deployment
Verify a config.json5 file has no syntax errors before pushing to production. Open config.json5, copy contents, paste into validator, click Validate JSON5, fix any reported errors like unclosed comments or missing commas, validate again, and deploy once clean.
{appName: 'MyApp',version: '1.0.0',debug: true,database: {host: 'localhost',port: 5432,name: 'myapp_db',},features: ['auth','logging','monitoring', // trailing comma allowed
],}API response validation with comments
Confirm an API returns valid JSON5 before parsing in production. Copy the response body, paste into the validator, click Validate JSON5, review errors, fix unclosed brackets or malformed comments, re-validate, and proceed with integration once valid.
{status: 'success',data: {users: [{ id: 1, name: 'John' },{ id: 2, name: 'Jane' },],},timestamp: 1642684800,}Package.json5 validation for npm projects
Ensure package.json5 meets format requirements for npm tooling. Generate package file, paste JSON5 into validator, click Validate JSON5, check for comment issues or invalid property names, fix problems, re-validate, and commit once valid.
{name: 'my-package',version: '1.0.0',description: 'A sample package',scripts: {start: 'node index.js',test: 'jest',},dependencies: {express: '^4.18.0',},}Quick validation guide
Who benefits from this JSON5 validator
Backend Developers
Validate configuration files and API responses before deployment
Frontend Developers
Check JSON5 data structures received from web services
QA Engineers
Test JSON5 parsing in applications and report format issues
Data Analysts
Verify exported JSON5 files meet format requirements
DevOps Engineers
Validate infrastructure configuration files and deployment manifests
Features and considerations
Browser-only processing
Keeps JSON5 data private and secure. No server uploads or data transmission.
Instant validation
Line-by-line error reporting speeds debugging. Auto-validation on typing provides real-time feedback.
Comment support
Validates single-line and multi-line comments according to JSON5 specifications.
Syntax only
Schema validation against JSON Schema requires separate tools after confirming basic structure.
File size limits
Large files over 1MB slow browser performance. Split large documents into smaller chunks.
Comment nesting
Nested comments are not supported in JSON5. Ensure comments are properly closed before opening new ones.
Best practices and common pitfalls
Use comments for documentation
Include single-line (//) or multi-line () comments to document configuration values and structure.
Trailing commas are allowed
Use trailing commas in objects and arrays to make diffs cleaner when adding new items.
Unquoted keys when safe
Use unquoted property names for simple identifiers. Quote keys containing special characters or reserved words.
Single quotes for strings
Use single quotes for string values to reduce escaping when strings contain double quotes.
Avoid nested comments
Nested comments are not supported. Ensure each comment block is properly closed before starting another.
Don't mix quote types incorrectly
Ensure string quotes match. Single-quoted strings must close with single quotes, double-quoted strings with double quotes.
How this JSON5 validator works
Front-end JavaScript uses a JSON5 parser to validate JSON5 strings and detect syntax errors. The parser checks for well-formedness according to JSON5 specifications. It handles comment removal, trailing comma validation, unquoted key checking, and single-quoted string parsing. Manual validation routines scan for unclosed brackets, mismatched braces, invalid comment syntax, unclosed strings, and structural issues. Error detection includes line number tracking, error type classification, and detailed message generation. The Ace editor provides syntax highlighting with JSON mode, making code easier to read and edit. Auto-validation triggers after a one-second delay when typing stops, providing real-time feedback. All processing occurs in the browser, so no data leaves your device.
Accuracy notes and limitations
- Validation follows JSON5 specification rules. Schema validation against JSON Schema requires external tools.
- Large files over 1MB cause browser performance issues. Split large documents into smaller chunks for validation.
- Comment parsing handles single-line (//) and multi-line () comments. Nested comments are not supported.
- Error line numbers are approximate for multi-line elements. Use error messages as guides rather than exact positions.
- Trailing comma validation checks for proper placement but does not validate semantic correctness of values.
About Toolexe team
Toolexe builds lightweight validation utilities for developers, QA engineers, and data analysts. The team reviews this validator weekly and updates error detection logic when JSON5 standards evolve. Last reviewed: February 6, 2026 by Toolexe QA (JH). For support or suggestions, use the Contact Us page.
Trust cues: browser-only processing, visible validation rules, and clear error reporting. For feedback or issues, send a note through the Contact Us page.
