JSON Validator Online: Find Syntax Errors Fast

When you need a JSON validator

Frontend throws Unexpected token, backends reject payloads, config centers fail to load—first check: is this text valid JSON?

ComTools JSON Validator (Tools/Json/Validator) runs JSON.parse in the browser: success shows a valid message (and can pretty-print with your indent); failure surfaces the engine error so you can fix the syntax.

Steps

1. Open JSON Validator.
2. Paste text (or use Sample).
3. Optionally pick indent (2 / 4 / Tab) for the pretty view on success.
4. Click Run.
5. Read the status: valid, or the parse error details.

Nothing is uploaded—validation is local.

Valid vs invalid examples

Valid

{
  "id": 1,
  "name": "Alice",
  "active": true,
  "tags": ["a", "b"],
  "meta": null
}

Common invalid patterns

Issue	Bad example	Fix
Trailing comma	{"a":1,}	Remove the last comma
Single quotes	{'a':1}	Use "a"
Unquoted keys	{a:1}	"a": 1
Comments	{"a":1 // x}	Not allowed in JSON
Trailing array comma	[1,2,]	Remove trailing comma
Unescaped quotes	{"msg":"say "hi""}	Use \"
NaN / JS-only values	{ "n": NaN }	Use null or a string

Browser messages often look like: Unexpected token ... in JSON at position N—jump near that offset.

After it validates

Next step	Tool
Readable view	JSON Formatter
One line	JSON Minify
Diff two responses	JSON Compare
C# classes	JSON to C#
Array → INSERT	JSON to SQL
Extract fields	JSONPath

Validator vs formatter

• Validator: pass/fail first; may pretty-print on success.
• Formatter: indent, highlight, fold; also errors on invalid JSON.

Use the validator for a quick green/red check; use the formatter to browse large documents.

Notes

• JSON ≠ JavaScript objects: no undefined, functions, NaN, or trailing commas.
• Dates are usually ISO strings, not a native Date type.
• Huge payloads can freeze the tab—validate a subtree first if needed.

FAQ

How do I use position N?
Count characters from the start (including newlines), or search near , ' { in the snippet.

JSON5 / YAML?
Strict JSON only. Convert loose formats to standard JSON first.

Empty input?
Treated as invalid.

Array root OK?
Yes—[1,2,3] and {...} are both valid roots.

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