Online JSON Validator & Checker

Instantly validate and check your JSON data for syntax errors, formatting issues, and structure problems—right in your browser. This free real-time JSON validator helps developers, analysts, and students catch mistakes fast, understand error messages, and ensure your data is ready for APIs, configuration files, or data exchange. No downloads or registration—just paste, validate, and fix.

Developers collaborating on data validation tasks

Validate & Format Your JSON Instantly

Paste or type your JSON below. The validator checks your input in real time, highlights errors, and shows the parsed result if valid. Use this free tool to fix syntax issues, reformat messy JSON, and prepare data for API integration or configuration files.

Tip: Validation and pretty-printing happen as you type. Errors are highlighted below.










How to Use the JSON Validator


    

  1. Paste or type your JSON data into the input box.
    2. 

  2. View instant feedback. Errors are highlighted with details below the editor.
    3. 

  3. If valid, the tool shows pretty-printed JSON for easy reading and copying.
    4. 

  4. Click Clear to reset, or Validate to re-check after edits.
    5. 



Sample JSON: 


{
    "name": "MiniTweak",
    "type": "tool",
    "features": ["validation", "formatting"],
    "year": 2025
}


Try editing the sample to introduce a mistake (like remove a comma), then watch the live error feedback!






















Common JSON Mistakes Explained






Common Mistakes


    

  • Unquoted keys: All keys must be in double quotes.
    
{ name: "Alice" } ← Invalid 
    
{ "name": "Alice" } ← Valid

    • 

  • Single quotes instead of double: { 'name': 'Bob' } ← Invalid
    • 

  • Trailing commas: { "a":1, } ← Invalid
    • 

  • Missing or extra commas: { "a":1 "b":2 }
    • 

  • Improper nesting / brackets: { "a": [1,2 } 
    • 

  • Comments in JSON: // Not allowed ← Invalid
    • 











Best Practices


    

  • Always use double quotes for both keys and string values.
    • 

  • Validate and format your JSON before sending it to an API or saving to a file.
    • 

  • Keep structures consistent—avoid deeply nested objects where possible.
    • 

  • Don’t include comments—JSON does not support them.
    • 

  • Use UTF-8 encoding for all JSON data. Avoid special control characters.
    • 



Tip: Use dedicated tools for formatting JSON for readability.










Why These Mistakes Happen





JSON is strict!

                            Even small typos—like a missing quote or extra comma—will break your data. Most errors come from copying JavaScript objects (which allow single quotes and unquoted keys) or editing by hand.
                        





Example: Trailing Comma Error

{
  "tool": "json-validator",
  "valid": true,  // ← This comma is fine
}

Error: Unexpected token } in JSON

Fix: Remove the comma after true.








Example: Single Quote Error

{ 'tool': 'json-validator' }

Error: Unexpected token ' in JSON

Fix: Replace single quotes with double quotes.




















JSON Error Messages Explained: What Do They Mean?














What it means: You have a typo—maybe a missing comma, bracket, or an invalid character.

Example: { "x": 1 "y": 2 }

How to fix: Add a comma between 1 and "y".

Other causes: Single quotes instead of double, comments, or trailing commas.
                        
















What it means: The JSON is incomplete. A bracket, brace, or quote is missing.

Example: { "a": [1, 2

How to fix: Add the missing closing ] and }.
                        
















What it means: There’s a string where the parser expects something else, typically missing a comma or colon.

Example: { "a" "b": 2 }

How to fix: Add a colon or comma as needed.
                        
















What it means: There’s an unescaped character or an illegal line break within a string value.

Example: { "a": "abc↵def" }

How to fix: Remove line breaks or escape special characters inside strings.
                        
















What it means: There’s a comma after the last item in an object or array, which JSON doesn’t allow.

Example: { "a": 1, }

How to fix: Remove the comma after the last item.
                        
















What it means: All property names must be in double quotes.

Example: { name: "Alice" }

How to fix: Change to { "name": "Alice" }.
                        

















    

  • Invalid number: Numbers like 0123 or NaN are not valid in JSON.
    • 

  • Comments: // ... or /* ... */ are not permitted in standard JSON.
    • 

  • Improper nesting: Be sure brackets [] and braces {} are correctly paired.
    • 





















Frequently Asked Questions about JSON Validation














                            JSON validation checks that your data follows strict JSON syntax rules: double-quoted keys/strings, no trailing commas, proper nesting, and no comments. Use our online JSON validator to instantly detect errors, get clear feedback, and ensure your data is safe for APIs, config files, or data exchange.
                        
















                            The most common causes are missing commas, single quotes, unquoted keys, or extra commas after the last item. Our validator highlights the error and location—see above for explanations of typical error messages and how to fix them.
                        
















                            No—JSON does not support comments. Any // or /* ... */ will cause a syntax error. If you need to annotate data, add a property like "_comment": "your note" inside the object.
                        
















                            “Unexpected token” usually means you have a misplaced or missing comma, bracket, or quote. Check the error location, look for typos, and compare your structure to a working example. Our validator will pinpoint the issue and suggest how to correct it.
                        
















                            Yes! JavaScript objects can use single quotes, unquoted keys, and trailing commas—JSON cannot. JSON is a strict data format for interchange and must use double quotes for keys/strings and no comments. Always validate before sending data to APIs or other systems.
                        
















                            Use our validator or try our JSON formatter tool to pretty-print and indent your data. Well-formatted JSON is easier to debug, review, and share.
                        
















                            Yes—the tool works entirely in your browser and does not send data anywhere. However, always be cautious with highly sensitive or personal information in any online tool. For best security practices, see our secure input validation guide.
                        
















                            JSON’s specification forbids commas after the last item in an object or array (unlike JavaScript). Trailing commas will always cause a parse error. Always remove the comma after the last property or array element.
                        

















Related Tools & Resources









JSON Formatter


Format, beautify, and re-indent JSON for easier reading and debugging.












JSON Minifier


Remove whitespace and compress JSON for APIs or storage.












CSV to JSON


Convert CSV spreadsheets to valid JSON for import or analysis.












Encoding/Decoding


Base64, URL, HTML entity, UTF-8 and more encoding/decoding tools for data safety.












Secure Input Validation


Best practices for validating untrusted data and securing web applications.