About this JSON merger

JoinJson is a free browser utility for combining two JSON documents and inspecting their differences. It is designed for applying configuration overrides, reviewing small updates, and preparing combined exports without a file-processing server.

What it does

The JSON merger follows three steps: add two inputs, choose merge rules, and review the result. Each input supports pasted text, a local .json file, or a public HTTPS URL. Live syntax validation helps locate errors. Matching keys use the second input’s value; optional deep merging combines nested objects, and arrays can be replaced or concatenated.

The result shows line numbers and highlights added keys and overridden values compared with the first input. Copy and Download export the complete result. The homepage does not join records by ID or validate application-specific schemas. Our separate guides explain approaches you can use in your own scripts.

How privacy works

Parsing and merging run in browser memory. The homepage does not save inputs or results in app storage. Loading a URL contacts the source host; ordinary page visits contact the hosting provider. Guide pages can save theme preferences. No live advertising or analytics vendor is enabled in the current template. See the Privacy Policy for limitations and future advertising disclosures.

Limitations and responsible use

Keep original files and inspect important fields before using a merged document. JSON syntax validation is not a correctness guarantee. Large or deeply nested inputs may exceed browser resources, and large numeric identifiers may lose JavaScript precision. Treat the guides as technical information rather than professional advice.

Learn and get in touch

Read the Python guide, ID join guide, and merge-method comparison. Send questions through the contact page. No user counts, performance comparisons, or search-ranking promises are claimed.

This site provides general information, not legal advice.