Free JSON Formatter & Validator
The most complete JSON tool online. Format, validate, explore as a tree, view arrays as a table, generate TypeScript interfaces, diff two JSONs, and apply smart transforms — all in one place, all running privately in your browser.
Not Just a Formatter
Every feature a developer actually needs when working with JSON, in a single tool.
Format & Validate
Instantly pretty-print or minify any JSON. Clear error messages show the exact line and position of syntax errors so you can fix them immediately.
Interactive Tree View
Explore nested JSON as a collapsible tree. Click any key or value to instantly copy its full dot-notation path. Collapse entire branches to focus on what matters.
Table View
When your JSON is an array of objects, switch to Table view to see it as a spreadsheet with sortable columns. Perfect for API responses and data exports.
TypeScript Generator
Paste any JSON and get production-ready TypeScript interfaces in one click. Handles deeply nested objects, arrays, optional fields, and union types automatically.
JSON Diff
Paste two JSON objects and see exactly what changed. Added keys highlighted in green, removed in red, changed values in amber. Line-by-line comparison.
Smart Transforms
Sort all keys alphabetically, remove null and undefined values, flatten nested objects into dot-notation keys, or stringify the entire JSON in one click.
Stats Panel
See your JSON's depth, total key count, array sizes, type breakdown, and byte size at a glance. Useful for debugging large API payloads.
Instant Copy & Download
Copy formatted or minified JSON to your clipboard with one click, or download it as a .json file. No extra steps, no popups.
100% Private
All processing happens in your browser. Your JSON data — which may contain sensitive API keys, tokens, or personal data — never touches any server.
Who Uses This Tool?
JSON is everywhere in modern development. This tool covers every workflow.
Developers
Debug API responses, validate configs, generate TypeScript types from backend payloads, and compare JSON before and after changes.
API Testing
Paste raw API responses to format and explore them. Use table view to quickly scan arrays of records from REST endpoints.
DevOps & Config
Validate JSON config files, sort keys for consistent diffs in version control, and minify configs for production deployments.
Students & Learners
Use tree view to understand deeply nested JSON structures visually. Great for learning how APIs and data formats work.
Frequently Asked Questions
What JSON errors can the validator detect?
The validator detects all standard JSON syntax errors: trailing commas, missing quotes around keys, single quotes instead of double quotes, unescaped special characters, mismatched brackets and braces, and invalid values like undefined or NaN. Error messages include the line number and character position to help you locate issues immediately.
How does the TypeScript interface generator work?
The generator recursively traverses your JSON structure and infers TypeScript types for every field. String fields become string, numbers become number, booleans become boolean, null becomes null, arrays become typed arrays like string[], and nested objects become named interfaces. When an array contains mixed types, it generates union types. The output is production-ready and can be pasted directly into your TypeScript project.
What does the Flatten transform do?
Flatten converts a deeply nested JSON object into a single-level object where keys use dot notation to represent the original hierarchy. For example, { "user": { "name": "Alex" } } becomes { "user.name": "Alex" }. This is useful for mapping nested API responses to flat database schemas or spreadsheet columns.
Is my JSON data sent to a server?
No. Every operation — formatting, validation, tree rendering, TypeScript generation, diffing, and all transforms — runs entirely in your browser using JavaScript. Your JSON data never leaves your device. This is especially important when your JSON contains API keys, authentication tokens, personal data, or confidential business information.
How does the JSON diff work?
The diff formatter formats both JSON inputs, then compares them line by line. Lines that exist in the second JSON but not the first are highlighted green (added). Lines in the first but not the second are highlighted red (removed). Lines that are identical appear in the normal style. This gives you an instant visual overview of what changed between two versions.
What is the Table view and when should I use it?
Table view is available when your JSON is an array of objects, such as a list of users, products, or API records. It renders the data as a spreadsheet with each key as a column header and each object as a row. You can click column headers to sort the table. This is far more readable than raw JSON for tabular data and is useful for quickly scanning large API responses.
What does Sort Keys do?
Sort Keys recursively alphabetises all object keys throughout your entire JSON structure, including nested objects. This makes JSON easier to read, produces consistent diffs in version control when keys are added or reordered, and is commonly used to normalise configuration files.
Can I use this for large JSON files?
Yes. Because all processing is done natively in the browser with no server round-trips, performance is limited only by your device. Most modern browsers handle JSON files of several megabytes without issues. For very large files (50MB+) some features like tree view may be slower as they require rendering many DOM elements.
Working with JSON: A Developer Guide
JSON (JavaScript Object Notation) has become the universal language of data exchange on the web. Originally derived from JavaScript object syntax, it is now used by virtually every programming language and platform as the default format for APIs, configuration files, databases, and data pipelines. Understanding how to read, write, validate, and transform JSON efficiently is one of the most practical skills a developer can have.
Why JSON Formatting Matters
Raw JSON from APIs and databases is typically minified — all whitespace removed to reduce transfer size. While efficient for machines, this is essentially unreadable for humans. A well-formatted JSON file with consistent indentation and line breaks makes structure immediately visible. It becomes obvious where objects begin and end, which keys belong to which level, and how arrays are structured. This readability directly reduces debugging time. When a developer can scan a formatted JSON response in seconds rather than mentally parsing a single line of minified text, they find and fix issues significantly faster.
TypeScript and JSON: A Perfect Pair
One of the most common developer workflows is receiving a JSON API response and needing to create TypeScript interfaces that match its structure. Doing this manually is tedious and error-prone — it is easy to miss fields, get types wrong, or forget to handle nullable values. Automatic TypeScript interface generation from JSON structure eliminates this friction entirely. You paste the response, click generate, and get correct interfaces that you can immediately use in your codebase. This is particularly valuable when integrating with third-party APIs where TypeScript definitions may not be available or may be outdated.
JSON in Configuration Files
Beyond APIs, JSON is the dominant format for application configuration. Package.json in Node.js projects, tsconfig.json for TypeScript, .eslintrc for linting rules, and dozens of other tooling config files all use JSON. These files benefit enormously from consistent key ordering, which makes diffs in version control cleaner and reduces merge conflicts. The sort keys transform is specifically useful here — alphabetically sorted keys mean that two developers adding different keys to the same object will produce a diff that clearly shows both additions without any noise from key reordering.
Common JSON Mistakes and How to Avoid Them
The most common JSON syntax errors are trailing commas (valid in JavaScript objects but illegal in JSON), single-quoted strings (JSON requires double quotes), comments (JSON has no comment syntax despite many config tools supporting them through extensions), and unquoted keys. These mistakes are invisible to the naked eye in large files but cause immediate parse failures. A JSON validator catches all of these instantly and points you to the exact location of the problem. Getting into the habit of validating JSON before committing it to version control or deploying it to production prevents a surprisingly common class of runtime errors.