JSON Merge
See combine multiple JSON objects into a single master document with configurable conflict resolution.
Last updated: April 28, 2026
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Deep merging recursively combines nested objects. If a key exists in both objects and both values are objects, they are merged. Otherwise, the second value overwrites the first.
All processing happens locally in your browser. Large files are handled in memory and never uploaded to any server.
JSON Merge
The JSON Merge tool allows you to join two or more JSON structures into one. Add inputs in the order they should apply, choose a shallow merge that only overwrites top-level keys or a deep recursive merge that descends through every nested object, and decide what happens when both sides define the same key: later inputs win, earlier inputs win, or a custom rule applies. Arrays can be concatenated, de-duplicated, or replaced outright. Every merge is previewed before you export, and value types are preserved exactly, so numbers stay numbers and nested objects stay objects rather than collapsing to strings. It is particularly useful for combining default configurations with environment-specific overrides or aggregating data from multiple API endpoints into a single object. The merge runs entirely in your browser, so none of the inputs are uploaded.
Why This Tool Exists
What makes this useful — and why I built it this way.
Unified Datasets: Combine multiple JSON structures into a single file.
Conflict Resolution: Manage key overlaps with simple merge priority controls.
Structure Optimization: Cleans and formats combined results automatically.
Predictable Previews: Inspect the exact merged output before you commit to downloading it.
Type Safety: Values keep their original JSON types through every merge step.
When You'd Use This
Real situations where this tool saves the day.
Configuration Merging: Combine project setting folders into single files.
Data Aggregation: Group separate JSON database dumps into unified feeds.
API Payload Building: Build complex payloads by merging separate data variables.
Environment Overlays: Layer local development settings on top of shared defaults.
Endpoint Aggregation: Combine paginated API responses into one master object for analysis.
Using JSON Merge
It's straightforward — here's how it works.
Add the JSON objects you want to merge, in the order they should apply.
Configure the merge strategy (Deep vs Shallow).
Decide how to handle duplicate keys (Overwrite vs Keep Both).
Choose how arrays combine: concatenate, remove duplicates, or let the last input win.
Preview the merged result, then generate and download the JSON.
Questions People Ask
Honest answers about how this works.
How are arrays handled?
Short answer: You can choose to either concatenate arrays, unique-merge them, or have the second array overwrite the first.
Do my JSON files get uploaded during a merge?
No. Every input is parsed, merged, and previewed locally in your browser, so configuration files, API dumps, or datasets containing sensitive records never leave your device. The merged result exists only in the page, and closing the tab discards all inputs from memory.
Deep merge vs shallow merge, what is the difference?
A shallow merge only looks at top-level keys, so an object value in the later input replaces the earlier one wholesale. A deep merge walks both objects together and combines their nested keys, so defaults deep in the tree survive unless explicitly overridden.
Why is one of my values missing from the result?
Some key exists in more than one input. With overwrite rules, the later value replaces the earlier one, so a value you expected to keep can disappear. Check the conflict resolution setting and the order of your inputs, then re-run the merge to confirm.
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