JSON formatter and validator
Validate JSON syntax and choose readable indentation or compact output. Inspect configuration and API examples without uploading them. Formatting preserves numeric spelling, string escapes, key order and duplicate keys.
Free to use. No email or account required.
Your inputs
Calculations run in your browser. Inputs are not saved or sent to analytics.
Your result
Complete the inputs to see your result.
How it works
- Grammar is validated first. The formatter then changes whitespace between original tokens instead of serializing parsed numbers. This preserves integers larger than JavaScript’s safe-integer range without rounding them.
- Worked example
- {"id":9,007,199,254,740,993,"value":1.00} → 9,007,199,254,740,993; 1.00
Assumptions and limitations
Strict JSON only: no comments, trailing commas, undefined or NaN. Limit: 200,000 UTF-16 code units and nesting depth 100. Syntax validity does not verify an application schema. Duplicate keys are preserved, but consumers may interpret them differently; review them before use.
How to use this tool
Paste JSON, choose indentation and format it. Read validation feedback before copying or downloading; formatting preserves numeric tokens, key order and duplicate members.
When this is useful
Inspect an API fixture or improve a configuration file’s readability. This validates JSON grammar, not an application schema; receiving software may handle duplicate keys differently.
Sources
- IETF RFC 8259 — JSON syntax and interoperability Sources reviewed: 2026-10-28
Processing and privacy
The calculation or transformation runs in your browser. The tool does not send its input values or generated output to an application server. Loading a page still makes infrastructure requests; optional analytics and Google consent messages have separate controls.
Privacy Policy. Privacy & preferences in the footer controls optional analytics.
Sources and maintenance
Maintained by emonster. Sources are listed with their own review dates; these are not live-data timestamps or claims of independent expert certification.
