Merge multiple JSON objects or arrays with deep merge, shallow merge, or join-by-key (like a SQL join). Combine config, enrich datasets, and resolve conflicts. 100% client-side.
Combining JSON from multiple sources is a common but surprisingly fiddly task — a naive merge either loses nested data or overwrites the wrong thing. This tool gives you proper control with three strategies. Deep merge recursively combines nested objects, so overlapping configuration is merged key by key instead of being clobbered. Shallow merge keeps it simple at the top level. And join by key merges arrays of objects on a shared field, like stitching two database tables together.
You can add as many JSON inputs as you need, and the merged result updates live as you type or paste. Each input is validated independently, so a syntax error in one block is pinpointed without breaking the others. Everything runs in your browser, keeping your data private.
Join Arrays by Key — Like a SQL Join
The standout feature is the join-by-key strategy, which very few free tools offer well. Point it at a key such as "id" or "email", and it will merge records from every input array that share the same value for that key, combining all their fields into one object. Records that do not have the key are kept intact. This is perfect for enriching one dataset with fields from another — for example, joining a list of users with a list of their orders, or merging translated strings from several locale files.
For deep merges you can also choose whether arrays should replace each other or concatenate, giving you precise control over the outcome. The merged JSON can be copied or downloaded in one click, formatted and ready to use.
How to use this Merge JSON?
1
Add Inputs
Paste two or more JSON objects or arrays into the input blocks.
2
Pick a Strategy
Choose deep merge, shallow merge, or join-by-key for arrays of objects.
3
Set Options
For join-by-key, enter the key to match on (e.g. id); for deep merge, choose array behaviour.
4
Copy Result
The merged JSON updates live — copy or download it in one click.
Frequently Asked Questions
A shallow merge only combines the top-level keys — if two inputs both have a "settings" object, the second one completely replaces the first. A deep merge goes further and recursively merges nested objects, so "settings" from both inputs are combined key by key. Deep merge is what you usually want for configuration files.
Join by key treats each input as an array of objects and merges records that share the same value for a key you choose — much like a SQL join. For example, joining two user lists on "id" combines matching users into a single record with all their fields. It is ideal for stitching together data from different sources.
When two inputs set the same key to different values, the later input wins. For arrays in deep merge, you can choose whether they replace each other (default) or concatenate. This "last wins" rule is applied consistently across all strategies.
Yes. Click "Add JSON" to include as many inputs as you like. They are merged in order from top to bottom, so later blocks take precedence over earlier ones.
No. All merging happens locally in your browser. Your JSON never leaves your device, so it is safe to merge private data, API responses, or configuration files.