About JSON Validator — Find Syntax Errors with Line & Column
A single trailing comma or unquoted key in a 10,000-line JSON file can crash your application, and the error messages from most parsers are unhelpful — they tell you something broke but not where. This validator pinpoints the exact line and column of every syntax error, catches the patterns that cause most failures (trailing commas, single quotes, unquoted keys, unclosed brackets), and formats valid JSON into a readable structure. It also supports JSON5 and JSON-with-Comments for configuration files like tsconfig.json that use relaxed syntax.
How to Use This Tool
Follow these simple steps to get accurate results in seconds. The whole process takes less than a minute for most inputs.
- 1
Paste Your JSON
Copy your JSON string from any source — an API response, a configuration file, or a code editor — and paste it into the input area.
- 2
Review the Validation Result
If the JSON is valid, a success message appears. If there are errors, the exact line number, column position, and a description of the problem are displayed.
- 3
Fix Errors and Re-Validate
Use the error information to correct your JSON in the input area, then re-validate to confirm the fix. The instant feedback loop lets you iterate through corrections quickly.
- 4
Format the Validated JSON
Once your JSON passes validation, click the format button to beautify it with consistent indentation. The formatted output is easier to read and review.
- 5
Copy the Result
Copy the formatted JSON to your clipboard for pasting into your code editor, configuration file, or documentation.
How It Works
The technical details of how this tool processes your input and produces accurate results.
Parse Attempt with Error Capture
The validator passes your input to the browser's native JSON.parse() method. If parsing succeeds, the JSON is valid. If it throws a SyntaxError, the tool extracts the error message and attempts to determine the line and column of the offending character by analyzing the error position against your original input text.
Pattern Matching for Common Mistakes
After the initial parse, the validator runs a second pass using regular expressions and tokenization to detect specific error patterns that the native parser reports generically. This includes scanning for trailing commas before closing braces, single-quoted strings, unquoted property names, and hex numbers — patterns that are syntactically invalid but commonly written by developers editing JSON by hand.
Conditional Re-Parsing for JSON5 and JSONC
When JSON5 or JSONC mode is enabled, the validator preprocesses your input to strip inline comments (// and /* */), remove trailing commas before closing brackets, and normalize single quotes to double quotes before running the parse. This lets the same underlying parser handle relaxed syntax variants without requiring a separate JSON5 library.
Key Features
Built to handle real workflows quickly and accurately. Each feature solves a specific problem you'd otherwise need multiple tools or manual steps to address.
Precise Error Location Reporting
When validation fails, the tool reports the exact line number and column position of the error along with a human-readable description of what went wrong, such as a missing comma, unclosed bracket, or unexpected token.
Auto-Format and Beautify
After validation passes, format your JSON with consistent 2-space or 4-space indentation with one click. Turn minified single-line JSON into a readable tree structure without changing the data.
Common Error Pattern Detection
The validator identifies frequent mistakes like trailing commas before closing braces, single quotes where double quotes are required, and unquoted property names — issues that strict parsers reject but that are easy to overlook when editing by hand.
JSON5 and Comment Tolerance
Toggle support for relaxed JSON syntax including trailing commas, single-quoted strings, and inline comments. This accommodates configuration files that use JSON5 or JSONC format which strict validators reject.
Benefits of Using JSON Validator — Find Syntax Errors with Line & Column
Why this tool matters and how it improves your daily work.
Line-and-Column Error Messages Beat Runtime Parser Output
Node.js throws 'Unexpected token' at the end of a file, Python gives 'Expecting property name' — neither tells you which comma is missing. This tool points to the exact line and character, turning a 20-minute hunt into a 10-second fix.
JSON5 Mode Handles Configuration Files Out of the Box
VS Code settings, tsconfig.json, and .babelrc files use trailing commas and comments that strict JSON rejects. Toggle JSON5 mode and these files validate correctly without false positives.
Detect the Same Error Patterns You Make by Hand
The validator specifically looks for the mistakes humans make most: that trailing comma before a closing brace, the single quote you typed by muscle memory, the key you forgot to wrap in quotes. These patterns account for the majority of JSON parse failures.
Format Minified API Responses for Code Review
API responses arrive minified on a single line. After validating, auto-format with consistent indentation so you can actually read the structure during debugging and code review.
Common Use Cases
Real scenarios where this tool saves time and produces better results than manual methods.
API Payload Debugging
A 200-line request body fails to parse on your staging server. Paste it here, find the missing comma on line 47, fix it, and redeploy — instead of adding console.log statements to narrow down the error location.
Configuration File Verification
CI/CD pipelines, Docker Compose, and Terraform variable files all use JSON. A single syntax error blocks deployment. Validate these files before committing to catch errors that would only surface at deploy time.
Data Import Validation
Before bulk-importing a JSON export into MongoDB or Elasticsearch, validate the entire file. A malformed record midway through can silently truncate the import, losing data from that point forward without throwing an obvious error.
Learning and Teaching JSON Syntax
Students writing JSON by hand for the first time get cryptic 'unexpected token' errors from their IDE. This tool shows them exactly where and why their syntax is wrong — 'you used single quotes on line 3, JSON requires double quotes' — making the error educational rather than frustrating.
Who Uses This Tool
API Developers
validating JSON request and response payloads during integration testing, where a trailing comma in a 200-line request body crashes the endpoint with an unhelpful error message
DevOps Engineers
checking JSON configuration files for CI/CD pipelines and infrastructure-as-code templates before committing, preventing deployment failures caused by a single misplaced comma
Data Analysts
verifying JSON data exports before importing them into databases, ensuring that malformed JSON does not silently truncate or corrupt data during the import process
Pro Tips
Practical advice to get the most out of this tool, based on how experienced users actually work with it.
Always validate JSON after manually editing configuration files. A single misplaced comma or missing quote can break an entire application, and the error messages from most programming language parsers are far less helpful than the line-and-column output this tool provides.
When the validator reports an error on a specific line, check the line above it as well. Many JSON errors are caused by a missing comma on the preceding line, but the parser only detects the problem when it encounters the next element on the following line.
If your JSON passes validation but your application still fails, the issue may be a schema mismatch rather than a syntax error. Validate the structure against your expected schema — correct keys, value types, and required fields — separately from syntax validation.
Frequently Asked Questions
Quick answers to the most common questions about this tool. If your question isn't here, contact our support team.