SparkJSON / Online JSON Validator
Online JSON Validator
Use SparkJSON’s online JSON validator to check whether your document is valid JSON before you ship an API, config, or webhook. Get precise line and column errors, duplicate-key warnings, and a clear Valid badge — processed 100% client-side with zero server uploads.
Free SparkJSON tool — runs 100% in your browser. No signup, no upload, no paywall. This page opens in validate mode.
Why validate JSON online?
Invalid JSON breaks parsers silently or loudly depending on the stack. A dedicated JSON validator catches missing commas, unquoted keys, trailing commas (illegal in strict JSON), and bad escapes before they hit production.
SparkJSON goes beyond a boolean pass/fail: it shows where the parse failed and warns when duplicate keys would be silently overwritten by JSON.parse.
- Exact errors — line + column for every syntax failure.
- Duplicate keys — warnings when objects redefine the same key.
- No upload — validation never leaves your device.
Frequently asked questions
- How do I validate JSON online for free?
- Paste JSON into the editor and click Format & Validate (or press Ctrl + Enter). SparkJSON reports Invalid with a line/column message, or Valid when the document parses cleanly.
- Does valid JSON mean my API schema is correct?
- No. A JSON validator checks syntax only — not OpenAPI, JSON Schema, or business rules. After syntax passes, validate against your schema separately.
- Why does my JSON fail with a trailing comma?
- Strict JSON (RFC 8259) does not allow trailing commas. JavaScript object literals do. SparkJSON flags trailing commas so your payload works with strict parsers.