JSONLint.com

The JSON Validator, Formatter, and Toolkit for Developers

Overview

JSONLint is an online JSON validator, formatter, converter, and learning toolkit. It combines a multi-diagnostic parser, more than 40 browser-based tools, JSON Schema support, error-code references, practical guides, and free datasets.

Chrome Extension: Check out our JSON Formatter Chrome Extension for formatting JSON directly in your browser. (GitHub Repo)

Open-source validation engine

The main validator is powered by @jsonlint/core, the open-source diagnostics engine extracted from JSONLint. One pass returns every error and warning with stable codes, precise offsets, and line/column locations.

npm install @jsonlint/core

JSONLint documents all 34 diagnostics at jsonlint.com/errors, with an explanation, invalid and corrected examples, and a suggested fix for each code.

Features

Core Tools (40+ Total)

Validators & Formatters

• JSON Validator — Reports every error and warning in one pass, with stable diagnostic codes, precise line/column locations, and linked explanations
• Pretty Print — Format JSON with customizable indentation (2/4 spaces, tabs)
• Minify — Compress JSON by removing all whitespace
• JSON Sorter — Sort object keys alphabetically (ascending/descending)
• Escape/Unescape — Escape JSON for embedding in strings or unescape stringified JSON
• Stringify — Convert JSON to escaped string format
• JSON Repair — Auto-fix broken JSON (trailing commas, single quotes, comments, truncated data)
• JSONC to JSON — Strip comments and trailing commas from JSONC/JSON5 files
• Error Analyzer — Detailed error explanations with suggestions and auto-fix

Viewers & Query Tools

• Tree Viewer — Interactive collapsible tree visualization with color-coded types
• Table Viewer — Display JSON arrays as sortable HTML tables
• JSON Diff — Compare two JSON objects with highlighted differences
• JSON Path Query — Extract data using JSONPath expressions
• JSON Search — Find keys and values with full-text search
• Size Analyzer — Analyze JSON size, depth, and structure complexity
• Flatten/Unflatten — Convert nested JSON to dot notation and back

LLM & AI Tools

• Token Counter — Count tokens for GPT-4, Claude, and other LLMs

Encoding Tools

• Base64 Encode/Decode — Encode JSON to Base64 or decode Base64 to JSON
• JWT Decoder — Decode and inspect JWT tokens (header, payload, signature)

Data Converters

From	To
JSON	CSV, Excel, YAML, XML, SQL, Markdown
CSV	JSON
Excel	JSON
YAML	JSON
XML	JSON
SQL (INSERT)	JSON

Code Generators Generate typed, production-ready code from JSON:

• TypeScript — Interfaces with optional/required properties
• Python — Dataclasses with type hints
• Java — POJOs with Jackson/Gson annotations
• C# — Classes with JsonProperty attributes
• Go — Structs with json tags
• Kotlin — Data classes with kotlinx.serialization/Moshi/Gson
• Swift — Codable structs with CodingKeys
• Rust — Serde-compatible structs with derive macros
• PHP — Classes with typed properties (PHP 8+)

Schema Tools

• Schema Validator — Validate against JSON Schema Draft 7, 2019-09, or 2020-12; the validator selects the matching Ajv implementation from $schema
• Schema Generator — Auto-generate JSON Schema from sample data

Free JSON Datasets

JSONLint provides 47 free, open-source JSON datasets for testing, learning, and development:

• Reference Data — Countries, languages, currencies, timezones, HTTP status codes
• Development — Programming languages, file extensions, config templates (package.json, tsconfig, ESLint)
• Mock Data — Users, products, orders, transactions, comments, notifications
• Geography — US states, continents, airports, mountains
• Fun — Emojis, emoticons, colors, lorem ipsum

Browse all datasets at jsonlint.com/datasets

Editor Features

• Monaco Editor (VS Code's editor engine) with Shiki syntax highlighting
• Syntax highlighting and bracket matching
• Error highlighting on specific lines
• Drag and drop file upload
• Copy to clipboard
• Keyboard shortcuts (Ctrl/Cmd+Enter to validate, Ctrl/Cmd+Shift+F to format)
• Dark/light theme with system detection
• Full-width toggle for larger workspaces
• IME support for Chinese (Bopomofo/Zhuyin), Japanese, and Korean input
• Mobile responsive

Smart Validation

The validator provides structured feedback beyond a single JSON.parse() exception:

• Multi-diagnostic parsing — Reports all detectable errors and warnings in one pass
• Stable error codes — Links each diagnostic to a dedicated /errors/{CODE} reference page
• Helpful hints — Covers uppercase literals, single quotes, unquoted keys, invalid escapes, missing separators, and more
• JSONC-aware guidance — Recognizes comments and trailing commas and suggests the appropriate conversion tools
• Warnings — Flags duplicate keys, precision loss, lone surrogates, and suspicious Windows-path escapes without marking otherwise-valid JSON as invalid
• Preserves formatting — Validation doesn't modify your input (no more 1.0 → 1 conversion)

Privacy

🔒 JSON documents are processed entirely in your browser. Document contents are never included in telemetry or sent to JSONLint's servers.

To improve the validator, JSONLint records a document-free 10% sample containing only aggregate signals: document length, diagnostic count and codes, validation result, mode, and engine latency. The collector clamps and allowlists every field before writing to Cloudflare Analytics Engine. See lib/shadow-telemetry.ts and workers/shadow/README.md.

Tech Stack

• Framework: Next.js 15 (App Router)
• Language: TypeScript
• Styling: Tailwind CSS
• Editor: Monaco Editor with Shiki syntax highlighting
• JSON syntax validation: @jsonlint/core
• JSON Schema validation: Ajv 8 with draft-specific 7, 2019-09, and 2020-12 builds
• Utilities: jsonpath-plus, fast-xml-parser, diff, and jsonrepair

Local Development

# Clone the repository
git clone https://github.com/circlecell/jsonlint.git
cd jsonlint
# Install dependencies
npm install
# Start development server
npm run dev
# Build for production
npm run build
# Start production server
npm start

Visit http://localhost:3000 to see the app.

Environment Variables

Create a .env.local file:

NEXT_PUBLIC_BASE_URL=https://jsonlint.com

Project Structure

jsonlint/
├── app/ # Next.js App Router pages
│ ├── page.tsx # Home (JSON Validator)
│ ├── tools/ # Tools directory page
│ ├── datasets/ # Datasets directory page
│ ├── learn/ # Learning resources
│ ├── errors/ # Diagnostic index and 34 error-code pages
│ ├── json-to-csv/ # Converter tools
│ ├── json-to-typescript/ # Code generators
│ ├── json-schema/ # Schema tools
│ ├── json-formatter/ # Formatter and Chrome-extension landing page
│ ├── jwt-decoder/ # JWT decoder tool
│ ├── json-base64/ # Base64 encode/decode
│ ├── about/ # About page
│ ├── sitemap.ts # Dynamic sitemap generator
│ └── [...slug]/ # Dynamic content pages
├── components/ # React components
│ ├── Header.tsx # Site header with navigation
│ ├── Footer.tsx # Site footer
│ ├── JsonEditor.tsx # Monaco editor wrapper
│ ├── JsonValidator.tsx # Main validator
│ ├── ToolNav.tsx # Tool navigation bar
│ ├── DatasetCard.tsx # Dataset preview card
│ └── ArticleLayout.tsx # Learn article layout
├── docs/ # Documentation & content
│ ├── content/ # Article markdown files
│ └── datasets/ # Dataset documentation (47 datasets)
├── lib/ # Utility functions
│ ├── jsonlint-core-integration.ts # Main validator adapter
│ ├── error-codes.ts # Diagnostic reference catalog
│ ├── shadow-telemetry.ts # Document-free sampled metrics
│ ├── json-utils.ts # Secondary parsing/formatting operations
│ ├── dataset-utils.ts # Dataset loading utilities
│ └── themes/ # Custom Shiki themes
├── public/ # Static assets
│ ├── datasets/ # JSON dataset files (47 datasets)
│ └── images/ # Logos, favicons, screenshots
├── workers/shadow/ # Cloudflare telemetry collector and query helpers
└── styles/
└── globals.css # Global styles & theme variables

URL Parameters

Pre-populate the editor using URL parameters:

• ?json={encoded-json} — Load JSON directly
• ?url={url} — Fetch JSON from a URL

Example:

https://jsonlint.com/?json=%7B%22hello%22%3A%22world%22%7D

Contributing

We welcome contributions! If you have suggestions, feature requests, or found a bug:

1. Create an Issue
2. Submit a Pull Request

Adding a New Tool

1. Create a new folder in app/ with the route name
2. Add the converter/tool component
3. Add the page to navigation in components/ToolNav.tsx and components/Footer.tsx
4. Add SEO content below the tool

Adding Content Pages

1. Create a .md file in docs/content/completed/
2. Include frontmatter with title and description
3. The page will be available at the corresponding URL and added to Learn and the sitemap automatically

Adding Datasets

1. Create a JSON file in public/datasets/
2. Create a corresponding .md file in docs/datasets/ with frontmatter
3. The dataset will appear at /datasets/{name} and in the datasets directory

License

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

Author

Created by Todd Garland — Founder of BuySellAds

Credits

• @jsonlint/core — Multi-diagnostic JSON parser used by the main validator
• Monaco Editor by Microsoft
• Douglas Crockford — JSON creator
• Zach Carter — Original jsonlint implementation

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jsonlint.com — Making JSON easier since 2010.