JSON Merge
Deep-merge two or more JSON documents into one — objects merged recursively, later values win, arrays replaced or concatenated. Runs in your browser; nothing is uploaded.
About this tool
JSON Merge deep-merges two or more JSON documents into one. Paste your JSON values one after another (separated by whitespace or a newline) — they're merged left to right.
The merge rules:
- Objects are merged recursively — nested objects combine key by key.
- Conflicts (a key set to different scalar/types) are resolved last-wins: the later document's value replaces the earlier one.
- Arrays are replaced by the later value by default; tick Concatenate arrays to append them instead.
Set Indent for the output (or 0 to minify). Everything runs locally in your browser via WebAssembly — your data is never uploaded.
Handy for
- Layering a base config with environment-specific overrides.
- Combining partial JSON responses or fixtures.
- Applying a "patch" object on top of a default.
FAQ
Can I delete a key by setting it to null in a later document?
No — this is a deep merge, not JSON Merge Patch (RFC 7386). A null in a
later document is treated as an ordinary value, so the key stays in the output
with the value null rather than being removed.
How do I separate the documents I paste in?
Just put whitespace or a newline between them — the input is read as a stream of JSON values, merged left to right. Two, three, or more documents all work; pasting a single document simply reformats it at your chosen indent.
Are arrays merged element by element?
No. When two arrays collide, the later one replaces the earlier by default, or is appended to it if you tick Concatenate arrays. There is no index-wise merging of array elements — only objects merge recursively.
Can I get minified output?
Yes — set Indent to 0 to emit the merged document on a single line.
Values 1–8 pretty-print with that many spaces per level (the default is 2).
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool json-merge '{"a": 1, "nested": {"x": 1}}
{"b": 2, "nested": {"y": 2}}'New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/json-merge/?documents=%7B%22a%22%3A%201%2C%20%22nested%22%3A%20%7B%22x%22%3A%201%7D%7D%0A%7B%22b%22%3A%202%2C%20%22nested%22%3A%20%7B%22y%22%3A%202%7D%7D&concat_arrays=true&indent=2Machine-readable descriptor: tool.json — title + parameters JSON Schema for agents.