Pasted text and .json files
Paste JSON directly or upload a .json file when you need to inspect a payload, config file, export, or structured data block.
Browser-side JSON Checker
JSON Checker validate, format, and check JSON files online
Paste JSON or upload a .json file to validate syntax, find errors, detect trailing commas and duplicate keys, and review the structure before uploading, submitting, or debugging your data.
Local JSON file checker
JSON Checker for pasted text and .json files
Use the JSON Checker before uploading JSON, debugging an API response, submitting a configuration file, or copying structured data. It validates syntax, flags trailing commas and duplicate keys, summarizes the structure, and keeps the file in your browser.
Your JSON stays in this browser tab. This JSON Checker does not upload pasted text or .json files.
Check status
Results will appear here
Paste JSON or upload a .json file, then run the JSON Checker to see validity, issues, structure details, and output size.
Issue list
0- No issues detected yet.
Structure summary
A structure summary appears after the JSON parses successfully.
Original
0
Output
0
Reduction
No reduction
How the JSON Checker reviews JSON files before submission
The JSON Checker gives you a practical pre-submit pass: validate syntax, surface warnings, then return copy-ready JSON.
Paste or upload JSON
Paste structured data or upload a .json file when you need a JSON File Checker before an import, API test, CMS paste, or deployment config change.
Find syntax and key issues
The JSON Syntax Checker reports parser errors with line and column details, flags trailing commas, and warns when duplicate keys may overwrite data.
Review structure and export
After validation, the JSON Checker shows root type, key counts, arrays, objects, max depth, file size, array length, and top-level keys before you copy or download.
JSON Checker features for safer uploads and API debugging
Use this JSON Validator, JSON Formatter, JSON Duplicate Key Checker, and JSON Trailing Comma Checker in one local browser workflow.
Syntax validation
Confirm that the JSON can be parsed before it reaches a stricter API, database import, upload form, or build step.
Trailing comma detection
Spot commas before a closing object or array bracket, a common reason JavaScript-like data fails as real JSON.
Duplicate key warnings
Detect repeated keys inside objects so you can avoid silent overwrites when JSON is parsed by common tools.
Structure summary
Review root type, total keys, objects, arrays, max depth, file size, root array length, and top-level keys.
Format, minify, copy, download
Keep the JSON Formatter and minifier workflow, then copy the result or download a formatted JSON file.
How to use the JSON Checker before uploading JSON
This JSON Checker is for syntax, structure, duplicate key, trailing comma, and size checks. It does not replace JSON Schema or API-specific business rules.
01
Paste JSON or upload a .json file
Start with the exact JSON you plan to upload, submit, debug, or copy. The JSON Checker reads pasted text and uploaded files locally in your browser.
- Supports pasted JSON
- Supports .json file upload
02
Run the JSON Checker and review issues
Check validity first. If the JSON is invalid, inspect the syntax error line and column, plus any trailing comma found by the local scanner.
Duplicate keys are reported as warnings because many parsers accept them but keep only the last value.
Check JSON 03
Format, minify, copy, or download JSON
When the JSON is valid, review the structure summary, format it for readability, minify it for transport, copy the result, or download the formatted JSON.
For API debugging, compare top-level keys and array length against the endpoint or configuration shape you expected.
Use resultJSON Checker FAQ
Answers about local processing, valid JSON, duplicate keys, trailing commas, file upload, and structure summaries.
What does this JSON Checker validate?
The JSON Checker validates standard JSON syntax in your browser, reports parser errors with line and column details when available, detects trailing commas, warns about duplicate keys, and summarizes the parsed structure.
Can I use the JSON Checker as a JSON File Checker?
Yes. You can upload a .json file or paste JSON text. The file is read locally in the browser so you can check it before uploading, submitting a config, or debugging an API payload.
Will this JSON Checker upload or store my JSON?
No. Validation, formatting, minifying, duplicate key checks, trailing comma checks, and structure summaries run locally in your browser tab.
Why does a trailing comma make JSON invalid?
JSON is stricter than a JavaScript object literal. A comma before a closing object or array bracket is not valid JSON, so the JSON Checker flags it as an error.
Why are duplicate keys shown as warnings?
Many JSON parsers accept duplicate keys but keep only the last value for that key. The JSON Checker warns about duplicates so you can avoid accidental data loss.
Does the JSON Checker validate JSON Schema?
No. This tool checks syntax, common JSON file issues, structure, file size, formatting, and minifying. It does not verify required fields, JSON Schema rules, or API-specific business logic.
Use the JSON Checker before your next upload
Paste JSON or upload a .json file when you need to catch syntax errors, trailing commas, duplicate keys, empty roots, size issues, and unexpected structure.
Format for review, minify for transport, copy the result, or download formatted JSON without sending your data away from the browser.
JSON Checker for local validation, formatting, minifying, duplicate key checks, trailing comma checks, and structure review.