JSON Duplicate Key Detector

How to use this developer tool

1. Paste raw json text or load a local file.
2. Review any available processing options.
3. Select Detect Duplicates or press Ctrl/Cmd + Enter.
4. Check the summary and diagnostics, then copy or download the result.

What this developer tool does

Find repeated property names in raw JSON before a parser discards the earlier values. The scanner tracks each object scope separately and reports the duplicate key with its line, column, and object path. This is useful when reviewing hand-edited configuration, generated payloads, or logs where ordinary JSON parsing would keep only the last occurrence.

Nothing is uploaded by the core tool. Closing or refreshing the tab clears the current input.

Example

Input

{
  "id": 1,
  "name": "first",
  "name": "second",
  "nested": { "id": 2, "id": 3 }
}

Result

Run the sample to see the generated result and its statistics.

Use cases

• Review API payloads and fixtures before committing them.
• Diagnose generated JSON during development or testing.
• Prepare documentation, migrations, and typed interfaces.

Tips for reliable output

• Keep a copy of the original input before applying structural changes.
• Run invalid and edge-case samples as well as the happy path.
• Review warnings instead of treating generated output as a final contract.
• Use version control when replacing schemas or fixtures.
• Test downstream consumers after changing keys or required fields.

Processing details

JSON Duplicate Key Detector runs with standard browser JavaScript and uses JSON syntax as defined by JSON.parse except where raw-source inspection is required.

Application-specific validation rules and remote references are not inferred. Very large documents are limited by the memory available to the browser tab.