Fix Invalid JSON - JSON Repair Tool Online

What is this JSON Formatter?

This is a free, real-time JSON formatter and validator that runs 100% in your browser. No data is sent to any server. It supports formatting (beautifying), minifying, sorting keys alphabetically, and real-time validation with line-accurate error messages.

How does JSON formatting work?

JSON.parse() converts your text into an in-memory JavaScript object, then JSON.stringify() renders it back with proper indentation. This also validates the JSON as a side effect " any syntax errors are caught and displayed with the exact character position.

Is my data safe?

All processing is done entirely in your browser's memory using JavaScript. No data is sent to any server. When you close this tab, the data is gone. This makes it safe to use with API keys, tokens, or private configuration files.

What does "Sort Keys" do?

It recursively sorts all object keys alphabetically throughout the entire JSON structure. Useful for comparing two JSON objects for differences or enforcing consistent key ordering in config files.

What is JSON minifying?

Minifying removes all whitespace, newlines, and indentation from valid JSON. The result is functionally identical but smaller " useful for reducing payload size in HTTP API responses or configuration files.

How to Use This Tool

Identify and fix JSON syntax errors with precise error messages that show exactly where the problem is.

Paste your broken JSON into the input pane.

The tool immediately runs JSON.parse() and displays the error type and character position (e.g., "Unexpected token , at position 456").

Navigate to the reported position in your input to find the problematic character.

Fix the error — common fixes include removing trailing commas, replacing single quotes with double quotes, and adding missing closing brackets.

Re-paste your fixed JSON and click "Format" to verify it now validates successfully.

What Is Fix Invalid JSON Tool?

This tool helps you fix invalid JSON by providing precise error diagnostics. Instead of a generic "invalid JSON" message, it tells you exactly what went wrong, what character caused the error, and where in the string it occurred.

The most common JSON errors are: trailing commas (valid in JS, not in JSON), single quotes instead of double quotes, unquoted object keys, JavaScript-specific values (undefined, NaN, Infinity), and missing/extra brackets.

By showing the exact error position, this tool lets you fix errors in seconds instead of manually scanning thousands of characters looking for a misplaced comma.

Why You Need This

Fix invalid JSON before it breaks your application:

Debug configuration files — a single syntax error in package.json, tsconfig.json, or .eslintrc.json can prevent your entire project from building.

Fix hand-edited JSON — manual editing often introduces trailing commas or mismatched quotes that are hard to spot visually.

Recover corrupted JSON from logs — log files sometimes truncate or corrupt JSON payloads. The error position helps you identify where the corruption starts.

Convert JavaScript objects to valid JSON — JS objects with single quotes and trailing commas need specific fixes to become valid JSON.

Pro Tips for Best Results

The error position counts characters from the start of the string, including whitespace. Copy your JSON into a text editor with character counting to find the exact position.
If you get multiple errors, fix the first one and re-validate. In JSON, one early error often causes cascading false errors later in the string.
Common fix pattern: replace all single quotes with double quotes, remove trailing commas, and wrap unquoted keys in double quotes.

Frequently Asked Questions

What are the most common JSON syntax errors?

In order of frequency: (1) Trailing commas after the last item in arrays/objects. (2) Single quotes instead of double quotes. (3) Unquoted object keys. (4) JavaScript values like undefined or NaN. (5) Missing closing brackets or braces. (6) Comments (// or /* */).

How do I convert a JavaScript object to valid JSON?

Replace single quotes with double quotes, remove trailing commas, quote all keys, remove comments, and replace undefined with null. Or use JSON.stringify(obj) in your browser console to do it automatically.

Why does JSON not allow trailing commas?

The JSON specification (RFC 8259) was designed to be a strict, unambiguous data format. Trailing commas were intentionally excluded to keep the grammar simple. JavaScript allows them for developer convenience, but JSON prioritizes interoperability across all programming languages.