Free online JSON deep merge tool. Combine two JSON objects recursively, merging nested properties instead of overwriting. Arrays are concatenated. Runs locally in your browser.
100% Local
How to Use the JSON Merge
Paste the first JSON object on the left and the second JSON object on the right. Click Merge to deep-merge them: nested objects are recursively combined, arrays are concatenated, and the second object takes precedence on scalar value conflicts. Use Clear to reset.
How the merge algorithm works
Nested objects are merged recursively — properties are combined, not overwritten
Arrays are concatenated end-to-end
On scalar conflicts, the second object's value wins
Keys present only in the first object are preserved
Features
Full recursive merge — no depth limit
Handles arrays, objects, strings, numbers, booleans and nulls
Validates both inputs before merging
All processing runs locally in your browser. Your data is not uploaded to any server.