JSON Merge

Deep merge two JSON objects. Nested objects merge recursively; arrays from the second object replace the first at the same key.

  • Runs entirely in your browser
  • No data stored or sent to a server
  • Free forever — no signup
  • Instant conversion

Input and Output

Use the interactive encoder and decoder on this page to process your text.

Learn more about merging JSON objects

How to Deep Merge JSON Objects

JSON Merging

When to Merge JSON

Combine default and override configs, merge API partial updates, or join environment-specific settings into one object. Paste two JSON objects — the second overrides the first at conflicting keys.

Real-World Examples

Base config + environment overrides → single deployable config

{"a":1,"b":{"x":1}} + {"b":{"y":2}} → {"a":1,"b":{"x":1,"y":2}}

Combine user defaults with saved preferences in a settings object

Common Mistakes

  • Expecting arrays to concatenate — arrays from the second object replace the first entirely
  • Shallow merge expectations — nested objects are merged recursively, not replaced wholesale
  • Merging invalid JSON — validate both inputs first

Developer Tips

  • Put defaults in the first object, overrides in the second
  • Sort keys after merging for stable config diffs in git
  • For precise diffs, use JSON Patch instead of full merge

Frequently asked questions

How are nested objects merged?

Nested objects are merged recursively. Keys from the second object override or extend keys in the first.

What happens to arrays?

Arrays are replaced, not merged element by element. The second object array wins at that key.

Which object takes priority?

The second JSON object wins on conflicting keys. Non-conflicting keys from both are preserved.