Free developer tool

Online JSON Formatter & Validator

Validate, clean, format, and minify JSON data with instant syntax highlighting and line-by-line error reports. Built for developers testing API payloads.

Examples

Free forever. No registration required. All processing runs locally for 100% privacy.

Common JSON Formats & Validation Rules

JSON Structure Description & Common Errors
{} Empty Object. The simplest valid JSON. Must use curly braces. Must not end with a semicolon.
[1, 2, 3] Ordered list of values. Items can be of different types. Trailing commas are invalid in strict JSON.
{"key": "value"} Double Quotes only. All keys must be double-quoted. Single quotes like 'name' are invalid.
{"active": true} Boolean & Null. Must use lowercase literals: true, false, and null. Capitalized values are invalid.
{"nested": {"id": 1}} Nested Structure. Objects containing other objects or arrays. All nesting must be balanced.

How the JSON Formatter & Validator Works

Continuum's JSON formatter parses raw strings using standard compliant parsers. If a parsing failure occurs, the validator catches the exception and extracts the exact line and byte position of the syntax error.

[Raw JSON string] ──> (Syntax Validation) ──> [Format (Indented) / Minify (Compact)]
                                  │
                                  └─── Validation Error? ──> [Exact Line & Character Highlight]

Standard strict JSON requires double quotes around both property keys and string values. Single quotes, trailing commas, comments (like // or /* */), or special NaN/Infinity values are not allowed in strict JSON and will be flagged as syntax errors by this tool.

Once validated, this tool allows you to instantly copy the beautified JSON to your clipboard for use in configuration files, API calls, or scenario assertions in Continuum.

Ready to Monitor your JSON APIs?

ContinuumNexus runs continuous automated tests against your REST APIs, extracting variables using JSONPath and verifying assertions on status code, headers, and payload content.

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Frequently Asked Questions

Is my JSON data sent to a server?
No. The formatting and validation runs entirely in your browser using local client-side processing, ensuring 100% privacy and security for your credentials or payload details.
Why is strict JSON validation important?
Strict JSON conformance ensures that standard web services, APIs, and configuration engines can reliably parse your payloads. Many libraries fail when encountering comments, single quotes, or trailing commas.
What are the most common JSON syntax errors?
The most frequent errors include using single quotes instead of double quotes, trailing commas in objects or arrays, missing commas between elements, and unbalanced brackets or braces.
Can I format minified JSON?
Yes. This tool takes any valid JSON structure—whether minified, compacted, or poorly formatted—and pretty-prints it with clean indentations and line spacing.
How does this connect to API monitoring in Continuum?
ContinuumNexus lets you define advanced assertions using JSONPath queries on your API response bodies. Using valid, well-structured payloads is the starting point for building reliable automated API monitoring monitors.