📦 JSON Formatter & Validator

How to Format & Validate JSON Online

JSON (JavaScript Object Notation) is the undisputed lingua franca of modern web APIs, configuration files, and database exports. However, APIs often deliver minified one-line JSON without whitespace, making it nearly impossible to read or debug.

Paste any JSON payload into the box above. FixMyString instantly parses the structure, highlights syntax errors, and beautifies the output with clean indentation. You can also minify JSON to remove all unnecessary whitespace for production use, or sort object keys alphabetically for consistent comparisons.

Understanding the JSON Data Types

JSON supports exactly six data types. Every valid JSON value must be one of the following:

• String: A sequence of Unicode characters wrapped in double quotes. Examples: "hello", "fixmystring.com", "2025-01-15". Strings can contain escape sequences like \n (newline), \t (tab), and \" (literal double quote).
• Number: An integer or floating-point value, without quotes. Examples: 42, 3.14, -7, 1.5e10. JSON does not support NaN, Infinity, or hexadecimal literals.
• Boolean: Either true or false (lowercase only). Unlike JavaScript, uppercase True or False are not valid JSON.
• Null: Represented as null (lowercase). Represents the absence of a value.
• Array: An ordered list of values enclosed in square brackets, separated by commas: [1, "two", true, null]. Arrays can be nested and can contain mixed types.
• Object: An unordered collection of key-value pairs enclosed in curly braces: {"name": "Alex", "age": 30}. Keys must be strings. Values can be any of the six types, including other objects or arrays.

Common JSON Errors & How to Fix Them

• Trailing commas: Trailing commas like [1, 2, 3,] or {"a": 1,} violate the JSON specification (RFC 8259). Remove the final comma before closing braces or brackets. This is one of the most common copy-paste errors when adapting JavaScript object literals for use as JSON.
• Single quotes: JSON strictly requires double quotes ("key": "value"). Single quotes like 'key' will cause a parse error. Many developers coming from Python or JavaScript ES6 template literals make this mistake.
• Unquoted keys: JavaScript object literals allow unquoted keys like {name: "John"}, but valid JSON requires quotes around every property name: {"name": "John"}.
• Comments: JSON does not support comments. Neither // inline nor /* block */ comments are allowed. Use a configuration format like JSONC, YAML, or TOML if you need human-readable comments in your config files.
• Incorrect boolean/null casing: True, False, and Null are not valid JSON. The correct spellings are lowercase: true, false, null.
• Missing commas between pairs: Every key-value pair inside an object and every element in an array must be separated by a comma. Forgetting the comma between two sibling keys is a frequent error: {"a": 1 "b": 2} should be {"a": 1, "b": 2}.
• Unclosed braces or brackets: Every opening { or [ must have a matching closing } or ]. The formatter will report exactly which line the mismatch occurs on.

JSON Formatting Options Explained

Indent Size: Controls how many spaces are used per nesting level. A 2-space indent is the most popular convention for JSON in configuration files and APIs (used by npm, ESLint, and Prettier by default). A 4-space indent is common in Python-generated JSON and certain API documentation standards. Tab indentation is sometimes used in codebases that prefer tabs over spaces for all file types.

Sort Keys: When enabled, all object keys are sorted alphabetically before output. This is invaluable for comparing two JSON objects for differences — when both are sorted, a simple text diff will highlight only genuine data changes rather than property reordering noise. It is also useful for ensuring consistent serialization when hashing JSON for caching or signature verification.

Minify: Removes all whitespace (spaces, tabs, newlines) from the JSON output. Minified JSON is smaller and therefore faster to transmit over HTTP. For a 10,000-element JSON array, minification can reduce file size by 20–35%. Most production APIs serve minified JSON; formatted JSON is for developer-facing documentation and debugging tools.

Practical Developer Use Cases

• Debugging REST API responses: Paste the raw response from curl, Postman, or browser DevTools into the formatter to inspect the structure visually before writing parsing code.
• Validating webhook payloads: When building an integration that receives webhooks (Stripe, GitHub, Slack), paste the example payload from the vendor's documentation to understand the exact structure before writing deserialization code.
• Config file management: package.json, tsconfig.json, eslint.config.json, and countless other developer config files use JSON. Format them for readability during review; minify only if file size is critical.
• Comparing API versions: Paste two versions of the same JSON schema, sort the keys in both, then use a text diff tool to identify exactly what changed between API versions.
• Database exports: MongoDB exports, Firebase snapshots, and many NoSQL database dumps are in JSON Lines (JSONL) format — one JSON object per line. Use the formatter to inspect individual records.
• JWT inspection: The payload section of a JSON Web Token (the middle part between the two dots) is Base64-encoded JSON. First decode it with the String Encoder tool, then paste the decoded text here to read the claims.

JSON vs. Related Formats

Understanding when to use JSON versus other data formats is an important architectural decision:

• JSON vs. XML: JSON is lighter, more readable, and natively supported in JavaScript environments. XML supports attributes, mixed content, and namespaces, making it better for document-oriented data. For pure data exchange between web services, JSON is almost universally preferred.
• JSON vs. CSV: CSV is ideal for tabular, homogeneous data (spreadsheets, database exports). JSON handles nested, hierarchical data that cannot be flattened into rows and columns. Use the CSV to JSON converter to migrate between the formats.
• JSON vs. YAML: YAML is a superset of JSON and is more human-writable (supports comments, fewer quotes, multi-line strings). YAML is common in DevOps config files (Kubernetes, GitHub Actions, Docker Compose). JSON is more widely supported in programming language standard libraries.

Related Tools

• CSV to JSON Converter — Convert CSV files and spreadsheets to JSON arrays.
• String Encoder/Decoder — Escape or unescape strings and Base64 payloads.
• SQL IN Clause Builder — Turn lists of values into database queries.
• List & Delimiter Converter — Transform delimited lists before importing them into JSON arrays.