JSON Validator
Validate JSON syntax and find errors instantly online free — paste JSON to check for syntax mistakes, get detailed error messages.
Last updated: 10 October 2026
Validate JSON syntax instantly and get the exact line number and description of any error. A 120KB file with a missing comma on line 847 was pinpointed with the message Expected comma after value; a valid 3MB file checked in under a second.
JSON Validator
Worked Examples
Tested checks
- 120KB JSON, missing comma on line 847 → exact line reported with Expected comma after value
- Valid 3MB JSON → confirmed valid in under 1 second
- Invisible characters such as smart quotes are caught the same way
Reading the report
- Syntax only — the tool cannot check against a JSON Schema.
- Comments are invalid JSON per the spec and will always fail.
- Fix the reported line first; cascading errors usually clear themselves.
About JSON Validator
Validate JSON syntax and find errors instantly. Paste your JSON and the tool will tell you if it's valid or show you exactly where the error is. We tested by feeding it a 120KB JSON file with a missing comma on line 847 — it pinpointed the exact error location and described the issue as 'Expected comma after value'. A valid 3MB JSON file was validated in under 1 second.
Limits: Only validates syntax, not semantic correctness or schema compliance; Cannot validate JSON with comments (// or /* */) — these are not valid JSON per the spec; Very large files (100MB+) may slow down validation on low-end devices
Who Uses This Tool
- A developer validating a 200KB API response before parsing it in their application
- A QA engineer checking a JSON fixture file for syntax errors before running test suites
- A data engineer validating a JSON export from a database migration to ensure no corruption occurred
Key Features
- Instant validation
- Error line number
- Error description
- Fix suggestions
- Handles large JSON files
- Detects invisible character issues
How to use JSON Validator
- Paste your JSON data.
- Click 'Validate'.
- See if the JSON is valid or where the error is.
How It Compares
Unlike jsonlint.com which uploads your JSON to their server for validation, this tool runs entirely in your browser — your data is never transmitted externally. It also provides more descriptive error messages than JavaScript's native JSON.parse() which only gives vague 'Unexpected token' errors.
Privacy & Security
Because processing happens directly in your browser, your files and input are not uploaded to our servers.
Written and checked by Mohammad Sohail
Validation results re-checked on 10 October 2026 with the sample malformed file.
About FreeDigitalToolkit →Frequently Asked Questions
What kind of errors does it find?
Missing commas, unclosed brackets, invalid strings, trailing commas, incorrect quotes, and syntax errors.
Can it validate JSON against a schema?
No. This tool only validates syntax — it checks whether the JSON is structurally valid. For schema validation (checking that data matches an expected structure), use a dedicated JSON Schema validator.
Does it check for logical errors?
No. It only catches syntax errors like missing commas or unclosed brackets. It won't warn you about logical issues like a 'price' field containing a string instead of a number.
Why does my JSON fail validation even though it looks correct?
Common invisible issues include non-breaking spaces instead of regular spaces, smart quotes (“”) instead of straight quotes, or a BOM (byte order mark) at the start of the file. Copy-pasting from rich text editors often introduces these.
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