01
Merge nested objects recursively
Nested object properties are combined at each level instead of replacing the entire parent object unnecessarily.
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JSON Merge
Merge 2 JSON documents online with recursive object merging, selectable conflict priority and replace, append or unique array strategies.
Recursive object merge Left or right conflict priority Conflict error mode Array replace
Objects are merged recursively. Scalar conflicts and arrays follow the selected strategies.
INPUT Developer source value *
Paste the base JSON document. Object properties are merged recursively with the second document. Example: {"name":"Trexmi","settings":{"theme":"dark"},"tags":["json"]}
Reading file…
Merged JSON
Combined JSON using the selected conflict and array strategies.
About the tool
What JSON Merge does
JSON Merge combines two valid JSON documents into one result. It is designed for configuration overlays, API fixture preparation, localization files, environment settings and other tasks where a base document must be combined with an update. Objects are merged recursively, while scalar conflicts and arrays follow the options selected in the workspace.
This free JSON Merge tool makes the merge rules explicit. You can prefer values from the second document, keep values from the first document or stop when incompatible values meet. Arrays can be replaced, appended in order or appended with duplicate values removed. The result remains valid JSON and is displayed separately from both sources so it can be reviewed before copying.
JSON Merge table of contents
How to use
- Paste the base JSON into the first source field. This can be an object, array or another valid JSON value.
- Paste the update JSON into the second source field and confirm that both documents are valid.
- Choose whether conflicts should use the second value, keep the first value or stop with an error.
- Select Replace, Append or Append unique for arrays, then run JSON Merge.
- Review the merged output with JSON Compare or format it with the JSON Formatter before deployment.
Built for the task
Why use JSON Merge?
Focused controls, predictable output, and a workflow designed around this exact transformation.
02
Control every value conflict
Choose right priority, left priority or error mode so the merge behavior matches a configuration or data workflow.
03
Choose how arrays are combined
Replace arrays, append both arrays in order or append only values that are not already present.
04
Review output before using it
The merged JSON remains separate from the two sources and can be copied only after you inspect the result.
Useful answers
Questions about JSON Merge
Practical details about input, output, privacy, limits, and the best way to use this tool.
Answer 01
What does JSON Merge do?
JSON Merge combines two valid JSON values. Objects are merged recursively, while value conflicts and arrays follow the selected options.
Answer 02
Which document has priority during a conflict?
You decide. Right priority uses the second document, left priority preserves the first document, and error mode stops the merge.
Answer 03
Can JSON Merge combine nested objects?
Yes. When both values at a property path are objects, their properties are merged recursively.
Answer 04
How are arrays merged?
Arrays can be replaced by the second array, appended in order, or appended while removing duplicate values.
Answer 05
Can I merge more than two JSON files?
This version merges two documents at a time. To combine more documents, merge the first pair and use the result as the first input for the next document.
Answer 06
Does JSON Merge change my original inputs?
No. The merged result is displayed separately, so both source fields remain available for review.
Answer 07
Why does conflict error mode stop the merge?
It is designed to prevent silent replacement. The tool stops when two non-object values at the same path differ.
Answer 08
How do I verify the merged result?
Run the result through JSON Validator and use JSON Compare or JSON Diff Viewer to inspect the final structure.
What does JSON Merge do?
JSON Merge combines two valid JSON values. Objects are merged recursively, while value conflicts and arrays follow the selected options.
Which document has priority during a conflict?
You decide. Right priority uses the second document, left priority preserves the first document, and error mode stops the merge.
Can JSON Merge combine nested objects?
Yes. When both values at a property path are objects, their properties are merged recursively.
How are arrays merged?
Arrays can be replaced by the second array, appended in order, or appended while removing duplicate values.
Can I merge more than two JSON files?
This version merges two documents at a time. To combine more documents, merge the first pair and use the result as the first input for the next document.
Does JSON Merge change my original inputs?
No. The merged result is displayed separately, so both source fields remain available for review.
Why does conflict error mode stop the merge?
It is designed to prevent silent replacement. The tool stops when two non-object values at the same path differ.
How do I verify the merged result?
Run the result through JSON Validator and use JSON Compare or JSON Diff Viewer to inspect the final structure.
How JSON value conflicts are handled
A conflict occurs when the same property path exists in both documents and the values cannot be recursively combined as objects. Right-priority mode uses the value from the second JSON and is useful for overrides. Left-priority mode preserves the original value. Error mode stops instead of choosing automatically, which is safer when silent replacement could hide a configuration problem.
Replace, append or uniquely append arrays
Array replacement treats the second array as the complete new value. Append mode concatenates both arrays and preserves duplicates. Unique append adds values from the second array only when an equivalent value is not already present. Arrays of complex objects may still require domain-specific identity rules, so review them carefully rather than assuming that two objects with different key order represent different records.
Common JSON Merge errors
Both sources must be complete valid JSON. JavaScript object syntax with unquoted keys, comments, single-quoted strings or trailing commas is not valid JSON. Error conflict mode can also stop a valid pair of documents intentionally when scalar values disagree. Large differences may be easier to understand after formatting both inputs first.
JSON Merge best practices
Keep a copy of the original documents, define the conflict rule before merging and avoid using array append when order or duplicates carry business meaning. Validate the final document with the JSON Validator. Use JSON Diff Viewer to inspect changes, and consult the official JSON specification RFC 8259 when input syntax is unclear.