JSON Trailing Comma – Find and Fix It Online

Standard JSON does not allow a comma after the final object property or array item. The repair workspace starts with a trailing-comma example and shows each removed comma before you use the corrected JSON.

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Paste malformed JSON or AI-generated structured output.

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Common invalid JSON examples

Load one broken syntax pattern at a time, run the repair, and compare the declared rule with the resulting repair log.

Trailing commas

Trailing comma

Remove commas that appear immediately before closing object or array delimiters without touching commas stored inside string values.

{"roles":["admin","editor",],"active":true,}

Review: Confirm that each removed comma was only formatting punctuation and did not represent an intentionally missing value.

JavaScript-style object

Trailing comma · Single-quoted string · Unquoted object key

Convert identifier-like keys and single-quoted strings from a JavaScript object literal into standard JSON syntax.

{
  name: 'VetaTool',
  features: ['repair', 'diff',],
}

Review: Review every inferred key and string boundary because apostrophes and JavaScript escaping can make the intended text ambiguous.

JavaScript comments

JavaScript comment

Remove line and block comments that are legal in some configuration formats but are not allowed by the JSON grammar.

{
  // feature flag
  "enabled": true /* temporary rollout */
}

Review: Check whether a removed comment contained operational context that should be preserved outside the repaired JSON document.

Markdown code fence

Markdown code fence

Strip one outer Markdown fence commonly added around JSON returned by chat assistants, documentation, or copied code blocks.

```json
{"name":"Ada","active":true}
```

Review: Verify that the fence wrapped the entire payload and that no explanatory prose outside the code block was discarded.

Unsupported JavaScript literals

Undefined value · Non-finite number

Replace undefined and non-finite numbers that JavaScript accepts but standard JSON cannot represent with reviewable null placeholders.

{"missing":undefined,"score":NaN,"limit":Infinity}

Review: Decide whether null is the correct business value, or whether the property should be removed or represented another way.

Missing and redundant commas

Missing comma · Redundant comma

Insert a separator between adjacent complete values and remove extra separators only where surrounding tokens identify the boundary.

{"first":1 "second":2,,"third":3}

Review: Confirm that inferred separators match the intended property boundaries and that no omitted value was represented by an empty slot.

Mismatched delimiters

Mismatched delimiter

Replace or add a closing brace or bracket when the nested token stack identifies one bounded structural mismatch.

{"items":[1,2,3}

Review: Inspect the surrounding nesting because heavily damaged objects can have more than one plausible brace or bracket completion.

Escaped JSON string

Escaped JSON string

Decode one outer JSON string layer when a field contains an escaped object or array instead of a directly nested JSON value.

{"payload":"{\"name\":\"Ada\",\"active\":true}"}

Review: Confirm that the field is intended to become a nested object rather than remain a string consumed by another downstream system.

Repair log

Run the repair to see each change and why it was made.

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JSON syntax repair

How to remove a trailing comma from JSON

JavaScript object literals and some configuration formats accept trailing commas, but standard JSON does not. The repair tool above removes a comma only when it appears immediately before the closing token of an object or array and records the change for review. This tool is free to use. No account or payment is required.

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What you can do here

  • Browser-local JSON processing
  • Route-specific malformed JSON example
  • Focused parser or repair guidance
  • Broken and corrected JSON example
  • Related JSON problem navigation
  • Trailing comma repair log

Steps

  1. Paste the invalid JSON or start with the preloaded trailing-comma example.
  2. Select Repair JSON and review the trailing-comma change.
  3. Copy the repaired output after confirming no value was intentionally omitted.

Where trailing commas appear

A trailing comma can appear after the last object property or the last array item. JSON.parse rejects both forms even though modern JavaScript often accepts them in source code.

  • {"name":"Ada",}
  • [1,2,3,]

Review generated JSON before replacing source data

Removing a trailing comma is deterministic when the comma sits directly before a closing delimiter, but review is still useful when malformed source may represent a missing value rather than accidental punctuation.

Trailing comma example

The final property is followed by a comma before the closing brace.

Invalid JSON

{"name":"Ada","active":true,}

Repaired JSON

{"name":"Ada","active":true}

Common questions

Frequently asked questions

Are trailing commas valid in JSON?

No. Standard JSON does not allow a comma after the final property in an object or the final item in an array.

Why does JavaScript allow syntax that JSON rejects?

JSON is a separate data format with a smaller grammar. JavaScript object and array literals support syntax features, including trailing commas, that JSON does not.

Can the repair tool remove trailing commas automatically?

Yes. A comma immediately before a closing brace or bracket is a deterministic repair rule and is reported in the repair log.

Recommended next steps

Missing Comma in JSONLocate adjacent properties or array values that need a separator.Single Quotes in JSONConvert JavaScript-style single-quoted keys and string values to valid JSON.JSON Repair Online – Fix Invalid JSONApply conservative syntax repairs and review every reported change.

Debugging a specific JSON issue? Browse JSON troubleshooting.