Merge JSON Objects
Merge JSON Objects requires two parsed, non-array top-level objects and returns {...first, ...second} with two-space formatting. A matching key from the second object replaces the first value completely, including an entire nested object; arrays are values rather than merge targets. There is no recursive merge, conflict report, schema validation, prototype-key policy, array strategy, or undo.
Runs locally — files stay on your deviceAre nested objects merged recursively?
No. The second nested value replaces the first at that top-level key.
Object spread performs a shallow overwrite
Only enumerable own top-level properties are copied into the result, in first-then-second order.
How it works
Both inputs pass JSON.parse and object/array checks; JavaScript object spread constructs the output.
Key concepts
Second wins
Duplicate top-level keys take the second value.
Nested replacement
No child-property reconciliation occurs.
When to use it
- Overlay a small flat configuration.
- Apply explicit top-level defaults and overrides.
- Combine objects when replacement is intended.
When not to use it
- Do not expect deep merge.
- Do not merge arrays or primitive roots.
- Do not accept unreviewed security-sensitive configuration keys.
Worked examples
Flat
- Input
{"a":1} + {"b":2}- Expected output
{"a":1,"b":2}
Keys combine.
Conflict
- Input
{"a":1} + {"a":2}- Expected output
{"a":2}
Second wins.
Nested
- Input
{"x":{"a":1}} + {"x":{"b":2}}- Expected output
{"x":{"b":2}}
a is lost.
Common mistakes
Expecting deep merge
Nested object is overwritten. Correction: Choose a documented recursive strategy.
Merging arrays
Top-level arrays are rejected. Correction: Define concatenation or index rules separately.
Missing conflict review
No warning is emitted. Correction: Compare keys before merge.
Best practices
- Use only when shallow precedence is intended.
- Review duplicate keys.
- Validate the resulting configuration against a schema.
Related operations and differences
CSV to JSON
Choose CSV to JSON when you need to convert a header-based CSV table to JSON.; use Merge JSON Objects specifically for json merge.
Extract JSON Values
Choose Extract JSON Values when you need to list every primitive value in a JSON document.; use Merge JSON Objects specifically for json merge.
JSON Beautifier
Choose JSON Beautifier when you need to format JSON with readable indentation.; use Merge JSON Objects specifically for json merge.
JSON Flattener
Choose JSON Flattener when you need to flatten nested objects into dot paths.; use Merge JSON Objects specifically for json merge.
JSON Key Sorter
Choose JSON Key Sorter when you need to sort object keys recursively.; use Merge JSON Objects specifically for json merge.
JSON Minifier
Choose JSON Minifier when you need to remove unnecessary JSON whitespace.; use Merge JSON Objects specifically for json merge.
Limitations and privacy
- Top-level objects only.
- Shallow second-wins spread; no deep strategy, array merge, conflict report, schema, safe-key policy, provenance, or patch output.
Input is processed locally in this browser and is not uploaded by the tool.
Frequently asked questions
Which object wins conflicts?
The second.
Are nested objects combined?
No.
Can arrays be merged?
Not as top-level inputs.
Is schema checked?
No.