JSON Repair Tool - Fix Invalid JSON Online
JSON Repair Tool
Runs entirely in your browser. Nothing is uploaded.
What Is
JSON repair is the process of mechanically correcting malformed JSON so that it conforms to the grammar defined in RFC 8259 without changing the underlying data. The specification is deliberately strict, and parsers enforce every rule. Six rules cause the overwhelming majority of failures. First, a comma may not appear immediately before a closing brace or bracket, which is legal in many programming languages and is the single most common defect in hand-written JSON. Second, object keys and string values must be wrapped in double quotes; single quotes and bare identifiers are rejected. Third, the format has no comment syntax at all, yet many people write // and /* */ comments into JSON because they learned JSON in a JavaScript context.
Fourth, every member of an object and every element of an array must be followed by a comma except the last one, and omitting one causes a cascade of confusing errors that point at the wrong line. Fifth, control characters such as raw newlines, carriage returns and tabs may not appear literally inside a string; they must be escaped as \n, \r and \t. Sixth, the document must be well formed from end to end, so a payload cut off by a buffer limit or an interrupted export will never parse no matter how it is escaped. A repair tool differs from a validator in what it does after detecting the problem. A validator reports an error and stops. A repair tool applies targeted, reversible transformations: removing a comma that is followed only by whitespace and a closing token, converting single-quoted strings to double-quoted ones, stripping comment tokens while respecting string boundaries, and escaping raw control characters.
The crucial design constraint is that repair must be conservative. A tool that silently deletes data to make a document parse is worse than no tool at all, because it turns a loud failure into silent corruption. The approach here is to change only what is provably wrong, keep the original text available so you can diff the result, and then run a real parse to confirm success. If the input is too damaged to fix automatically, the tool says so and hands the text back untouched instead of pretending.
How to Use
- Open the JSON Repair Tool in your browser. It runs entirely client-side, so nothing you paste is ever transmitted to a server or stored anywhere.
- Paste your broken JSON into the input area. This usually comes from an API response you could not parse, a configuration file that a formatter rejected, or text copied from a log or terminal window.
- Click Repair. The tool scans the text and applies targeted fixes for trailing commas, single quotes, unquoted keys, comments, missing commas and unescaped control characters.
- Check the Parse status indicator. A green Valid result means a strict RFC 8259 parser accepted the repaired output, so you can paste it straight back into your code.
- Review the fixes that were applied in the change list so you understand what was wrong and can correct the source of the problem instead of repeating it.
- Copy the repaired JSON using the copy button and drop it into your editor, terminal or application. If the document was truncated rather than malformed, repair cannot recover the missing bytes, so re-export the original data.
- Test the result in your actual application before shipping, because repair fixes syntax only and cannot restore values that were already lost upstream.
Examples
Input: {"name":"Ada","role":"engineer",}
Process:
Remove trailing comma before }Result: {"name": "Ada", "role": "engineer"} — parses as valid JSON
Input: {name: 'Ada', tags: ['math','logic'],}
Process:
Quote bare key, convert single quotes, drop trailing commaResult: {"name": "Ada", "tags": ["math", "logic"]} — parses as valid JSON
Input: { // user record "id": 7, "note": "line one line two" }
Process:
Strip // comment, escape raw newline inside stringResult: {
"id": 7,
"note": "line one\nline two"
} — parses as valid JSON
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Frequently Asked Questions
What kinds of JSON errors can this tool actually fix?
The tool repairs the syntax defects that cause the large majority of real-world parse failures: trailing commas immediately before a closing brace or bracket, single quotes used in place of double quotes, unquoted object keys, JavaScript line and block comments left inside the data, commas missing between object members or array elements, literal newlines, tabs and other control characters inside strings, and trailing garbage after the final closing token. Each fix is a targeted transformation rather than a blanket rewrite. Truncated or corrupted documents cannot be repaired, because the missing bytes no longer exist anywhere in the text you provide, so the tool reports those as unfixable rather than guessing at your data.
Why does my JSON fail with an error on a line that looks fine?
JSON parsers fail at the furthest point they successfully understood, which is often well past the actual mistake. A missing comma early in an object causes the parser to keep reading, treating the next key as a string value, and the reported error position drifts to a later line that is itself perfectly valid. This is why beginners so often inspect the wrong line. The fix is to look backwards from the reported position rather than forwards, and to check the separator between each pair of members. Running the input through this repair tool isolates the real defect quickly, because it removes the cascade and leaves you with the one genuinely malformed construct.
Is it safe to paste production data into an online JSON repair tool?
With this tool, yes, because the repair happens entirely inside your browser using client-side JavaScript. Your text is processed by code that was already downloaded and is running on your own machine, so the payload never travels over the network, is never written to a server log, and cannot be captured by the site owner. That property matters more than it sounds: broken payloads are frequently API responses containing customer records, authentication headers, webhook secrets or full stack traces. Many hosted online validators quietly log what you paste. Verify that any tool you use makes a client-side processing claim, and treat that claim as a reason to prefer tools that require no account and no upload.
Can repair change the meaning of my data?
No, provided the tool is conservative, and that is the constraint this implementation follows. Repair only alters constructs that cannot legally appear in valid JSON: a comma before a closing brace is removed, a single-quoted string is re-quoted with escaped double quotes where needed, a comment is stripped, a missing separator is inserted, and a raw control character is escaped. No key is renamed, no value is reformatted beyond insignificant whitespace, and no number or string literal is reinterpreted. Because every transformation is reversible by hand, you can read the change list and confirm the result still represents the data you intended. If the input cannot be repaired without guessing, the tool leaves it alone and says so.
Why did my JSON become invalid after I edited it in a text editor?
The most common causes are human and mechanical rather than exotic. A smart quote character or a typographic apostrophe slipped in from a word processor instead of a straight double quote. An auto-indent feature inserted trailing whitespace plus a comma after the last item in an object. A find and replace turned a value into something containing an unescaped quote or a raw newline. A YAML or JavaScript object was pasted directly into a .json file, bringing comments and single quotes with it. A truncated transfer left the document ending mid-structure. Any of these produce a file that looks correct to the eye but that a strict parser rejects immediately, which is exactly the situation this tool is built to resolve.
Does a valid result mean my API will accept the data?
No. Valid JSON only means the text satisfies the JSON grammar, so a parser can read it without error. Whether the document is also correct for your application is a separate question that syntax repair cannot answer. Field names must still match your schema, numbers must still be in valid ranges, required properties must be present, and nested structures must have the shape your server expects. A document can parse perfectly and still be rejected by a strict API validator. Treat the green Valid status as confirmation that you eliminated the parse error, then run the value through your own schema validation or test suite before sending it anywhere.