JSON Formatter & Validator: Free Online Tool

JSON (JavaScript Object Notation) is the universal data format. APIs return it. Config files use it. Databases store it. And at some point, every developer stares at a wall of minified JSON trying to find a missing comma.

A JSON formatter takes compressed or messy JSON and turns it into clean, indented, readable output. A JSON validator checks whether your JSON is actually valid — and tells you exactly where the error is if it is not.

The 7 Most Common JSON Errors

These account for roughly 90% of all JSON parsing failures. Learn them once and you will debug JSON in seconds.

1. Trailing Commas

JSON does not allow trailing commas. This is valid JavaScript but invalid JSON.

{ "name": "Alex", "age": 30, }

{ "name": "Alex", "age": 30 }

2. Single Quotes Instead of Double Quotes

JSON requires double quotes for all strings and keys. Single quotes are not valid.

{ 'name': 'Alex' }

{ "name": "Alex" }

3. Unquoted Keys

Unlike JavaScript objects, JSON keys must always be strings wrapped in double quotes.

{ name: "Alex" }

{ "name": "Alex" }

4. Comments

JSON does not support comments of any kind — no //, no /* */. If you need comments in a config file, consider JSONC or YAML instead.

5. Missing Commas Between Properties

Easy to miss when editing JSON by hand. The parser will usually point to the line after the missing comma.

{
  "name": "Alex"
  "age": 30
}

{
  "name": "Alex",
  "age": 30
}

6. Unescaped Special Characters in Strings

Backslashes, double quotes, tabs, and newlines inside strings must be escaped. Raw newlines inside a JSON string will break parsing.

{ "path": "C:\new\folder" }

{ "path": "C:\\new\\folder" }

7. Wrong Value Types

JSON supports strings, numbers, booleans (true/false), null, arrays, and objects. It does not support undefined, NaN, Infinity, functions, or dates as native types.

JSON Formatting Best Practices

• Use 2-space indentation for JSON files. It is the most common convention and keeps nesting readable without excessive horizontal scrolling.
• Sort keys alphabetically in config files. It makes diffs cleaner and helps teams find properties quickly.
• Validate before committing. Add a JSON lint step to your CI pipeline. A malformed JSON config can take down an entire deployment.
• Use a schema. JSON Schema lets you define the expected structure, types, and constraints for your JSON data. It catches errors before they reach production.
• Minify for production, format for development. Minified JSON saves bandwidth in API responses. Formatted JSON is what you read and debug locally.

When to Use JSON vs. Other Formats

JSON is best for API responses, config files consumed by code, and data interchange between services. It is universally supported and fast to parse.

YAML is better for human-edited config files (like Docker Compose or GitHub Actions) because it supports comments and is less noisy with punctuation.

TOML is cleaner than both for flat configuration files. Rust's Cargo uses it, and it is gaining traction in the Python ecosystem.

CSV is still the best choice for tabular data that non-developers need to open in Excel or Google Sheets.