How to Format, Validate, and Debug JSON Online

JSON Formatter Guide: Validate, Debug, and Format JSON Online

JSON (JavaScript Object Notation) is the universal language of modern web APIs. Every REST API call, webhook, and most configuration files use JSON. But raw API responses come minified — all on one line, impossible to read. A JSON formatter transforms them into readable, navigable structures.

JSON Syntax: The Six Rules

JSON has exactly six rules. Breaking any one makes the document invalid.

Rule 1 — Keys must be double-quoted: {"name": "Ravi"} is correct; {name: "Ravi"} and {'name': "Ravi"} are both wrong.

Rule 2 — String values use double quotes only: {"city": "Delhi"} is correct; {"city": 'Delhi'} is wrong.

Rule 3 — No trailing commas: {"a": 1, "b": 2} is correct; {"a": 1, "b": 2,} is wrong. Arrays: [1, 2, 3] correct; [1, 2, 3,] wrong.

Rule 4 — No comments: JSON supports no comment syntax. Use JSONC or JSON5 for human-edited config files where comments help.

Rule 5 — null not undefined: JSON has null but no undefined. Use null for absent values.

Rule 6 — Lowercase booleans and null: true and false lowercase always; True and False are Python, not JSON.

Common JSON Errors and Fixes

Error Message

Root Cause

Fix

|---|---|---|

Unexpected token	Missing comma or extra comma	Check between properties and after last item
Expected property name	Key without quotes	Wrap key in double quotes
Unexpected end of JSON	Unclosed bracket or brace	Count opening and closing delimiters
Unexpected token at position N	Trailing comma or syntax error	Check character at that position
Invalid character	Smart quotes or special characters	Replace curly quotes with straight double quotes

JSON Data Types Reference

JSON supports exactly seven value types: strings (double-quoted text), numbers (integer or decimal, no quotes), booleans (true or false, lowercase), null, arrays (ordered lists in square brackets), and objects (key-value pairs in curly braces). These types can be nested infinitely.

Numbers support integers (42), decimals (3.14), and scientific notation (6.022e23). JSON has no Date type — use ISO 8601 strings ("2024-01-15T10:30:00Z"). JSON has no binary type — use Base64 strings.

JSON in Different Contexts

API debugging: Copy a response body from browser DevTools Network tab, paste into Lazyblink JSON Formatter, instantly see the structure. Identify the exact field path you need for your code.

Configuration files: package.json, tsconfig.json, and .eslintrc all use JSON. Format before committing to make code reviews easier.

MongoDB and NoSQL: MongoDB uses BSON internally but JSON for queries and aggregations. Format complex aggregation pipelines before running.

AWS IAM policies: Cloud permission policies are JSON. Formatting is essential for spotting security configuration errors in nested policy structures.

JSON vs Related Formats

JSON is strict and machine-optimised. For human-editable config files, alternatives exist: JSON5 allows comments and trailing commas; JSONC allows // comments (used by VSCode settings.json); YAML uses indentation instead of brackets and supports comments with #; TOML is designed for config files with a natural key = value syntax.

Rule: For API communication and data exchange, always use strict JSON. For config files humans edit regularly, JSON5 or YAML are better choices.

Using Lazyblink JSON Formatter

Paste your JSON in the left panel. Errors highlight immediately with the problematic line and column. Valid JSON appears formatted with syntax highlighting on the right. Use Minify to compress back to one line before sending to APIs. Use Validate to check validity without reformatting. The formatter also supports converting JSON to other formats including YAML and handles JSONPath queries for extracting specific values from complex documents.