JSON Syntax Checker
Check JSON syntax with line-by-line feedback. Strict RFC 8259 conformance, works on JSON of any size, runs entirely in your browser. Pinpoints quotes, commas, brackets, and escape problems.
Valid vs invalid JSON
Strict JSON requires double-quoted keys, no trailing commas, and no comments. Anything else fails the parser — and the validator pinpoints the spot.
{
"name": "hcodx",
"version": 1,
"tags": ["dev", "tools"]
}{
"name": "hcodx",
"version": 1,
"tags": ["dev", "tools"],
}What you'll use this for
Anywhere strict JSON is consumed: HTTP APIs, configuration files, log lines, CI pipelines, database documents.
API debugging
Paste a response body, find the malformed key or stray comma before your client crashes on it.
Config file checks
Validate package.json, tsconfig.json, or any app config before committing.
Webhook payloads
Confirm the payload your service produces is parseable everywhere downstream.
NoSQL documents
Verify Mongo / DynamoDB documents before bulk insert.
How to validate JSON
Paste your JSON
Drop it into the left editor. CodeMirror highlights syntax as you type.
Click Validate
Or leave auto-validate on for live feedback. The parser runs locally — no server.
Read the report
If valid you'll see a tick plus the parsed object pretty-printed. If invalid you'll see the line, column, and a snippet around the error.
Fix and re-run
Edit the input, re-validate. Auto-validate keeps the report fresh while you type.
Frequently asked questions
Strict JSON syntax: valid quotes (double, never single), commas (between items, never trailing), brackets (matched {}/[]), and escape sequences (\n, \t, \", \\, \uXXXX).
No — for those, use the JSON5 formatter. This tool checks strict JSON (RFC 8259) only.
No — only reports errors. To reformat valid JSON, use the JSON formatter.
Yes. No signup, no limits, no ads.
No. Pure client-side. Your data never leaves your device.
About this validator
JSON is the most common interchange format on the web — but parsers are strict. A misplaced comma, an unquoted key, or a stray character will reject the whole document. This validator gives you fast, line-precise feedback so you don't lose time hunting.
What it checks
- Quotes — keys and string values must use
"(double quotes). - Commas — between items, no trailing commas in arrays or objects.
- Brackets — every
{and[needs a matching}/]. - Escapes —
\n,\t,\",\\,\uXXXXare valid; unknown\sequences fail. - Primitives —
true,false,null(case-sensitive), plus IEEE-754 numbers.
Why use a browser validator
- Private. Production secrets in your JSON never leave the device.
- Fast. No round-trip; results appear as you type.
- Honest. Uses the same
JSON.parseimplementation your Node.js / browser app uses, so a pass here is a pass everywhere.