JSON Validator & Linter Online — Validate & Fix JSON Free | TimeToProgram — Free

How to use the JSON Validator & Lint

Validation is live — results appear as you type:

Paste your JSON

Paste any JSON into the input panel. The validator starts checking automatically — no button click needed.

Read the results

The results panel shows either a green 'Valid JSON' banner with stats, or a red error list with exact line:column positions.

Check error details

Each error card shows the error code (e.g. TRAILING_COMMA), the human-readable message, and a suggested fix.

Auto-fix common issues

If auto-fixable issues are detected, the Auto-Fix button activates. Click it to remove trailing commas, fix single quotes, and strip comments automatically.

Review warnings

Even on valid JSON, check for yellow warnings like duplicate keys or mixed-type arrays that could cause bugs in your application.

When to use this tool

Use the JSON Validator whenever your application throws a JSON parse error and you need to pinpoint exactly what's wrong:

→Your API response is causing a parse error in your frontend or backend code
→You've hand-written a JSON config file and aren't sure it's valid
→You want to catch hidden issues like duplicate keys or deeply nested structures before they cause bugs
→You're copying JSON from a blog post or documentation that may contain errors
→You need to validate JSON before committing it to a repository or deploying to production

Frequently asked questions

Q:What JSON standard does this validator use?

This validator checks against RFC 8259, the current JSON standard. It uses the native browser JSON.parse() engine (V8 on Chrome/Edge, SpiderMonkey on Firefox) — the same engine that parses JSON in Node.js and most production environments.

Q:What are lint warnings vs errors?

Errors mean the JSON is syntactically invalid and will fail to parse in any language. Warnings mean the JSON is technically valid but has patterns that could cause bugs — like duplicate keys (the second value silently overwrites the first) or integers larger than Number.MAX_SAFE_INTEGER which lose precision in JavaScript.

Q:What does DUPLICATE_KEY mean?

A duplicate key means the same key appears twice in the same object, e.g. { "status": "ok", "status": "error" }. JSON parsers accept this without throwing, but behavior is undefined — most parsers keep the last value, silently discarding the first. This is almost always a bug.

Q:Can I validate JSON Schema with this tool?

This tool validates JSON syntax (is it well-formed?), not JSON Schema (does it match a specific structure?). For JSON Schema validation, check our JSON Schema Validator tool which accepts a schema definition and validates data against it.

Q:Why does my JSON have trailing comma errors?

Trailing commas (e.g. [1, 2, 3,]) are valid in JavaScript and TypeScript but not in JSON. This is a very common issue when copy-pasting from JS code into JSON config files. Use the Auto-Fix button to remove them instantly.