JSON Editor

JSON Editor is a desktop Java Swing application for inspecting and editing JSON files through a tree-based interface. It is designed for day-to-day JSON maintenance where you want to navigate nested data, edit values safely, and save valid JSON without hand-editing the whole file in a text editor.

The editor loads a JSON document into a navigable tree, shows the selected node as an editable value, and supports common structural operations such as adding, renaming, duplicating, deleting, moving, and searching nodes.

Features

• Open a .json file from the command line, file picker, recent-file history, or drag and drop.
• Browse nested object and array content in a JSON tree.
• Filter the tree by JSON path, visible key name, or value text.
• Edit values as typed JSON literals or raw text.
• Find text inside the active value editor with match highlighting and keyboard navigation.
• Add, rename, duplicate, delete, and reorder JSON nodes.
• Copy the selected node path.
• Save JSON as nested object/array data.
• Optionally flatten object keys on save through preferences.
• Detect duplicate JSON object keys after load and warn before saving.
• Switch between light and dark editor themes.
• Use localized UI strings from resource bundles.

Requirements

• Java 21 or newer
• Maven 3.9 or newer for local builds

Quickstart

Download the latest json-editor.jar from Github Releases: https://github.com/skanga/json-editor/releases and run it

java -jar json-editor.jar

Build and Run

Build the application first:

mvn package

Run without arguments to open the last file from history:

java -jar target/json-editor.jar

Start with a specific JSON file:

java -jar target/json-editor.jar path/to/file.json

Editing Model

Keys are represented as JSON paths. For example:

• /a/b means the b property inside object a.
• /a.b is a single property literally named a.b.
• /items/0/name means the name property on the first object in the items array.

Values are edited as JSON literals:

"hello"
true
42
null
["a", "b"]
{"enabled": true}

Use typed editing for normal values and raw editing when you need direct literal control.

Performance Notes

JSON Editor is tuned for everyday JSON files up to about 1 MB. It includes practical safeguards for larger files:

• warns before opening files over 10 MB;
• avoids restoring large expanded tree states;
• caps editor field height for long values;
• uses an indexed save path for large node counts;
• scans duplicate keys with a streaming reader so the preflight check does not materialize a second JSON tree.

Test

Run the full test suite:

mvn test

Run a package build:

mvn package

Project Structure

src/main/java/com/skanga/jsoneditor/editor   Swing editor UI and tree behavior
src/main/java/com/skanga/jsoneditor/io       JSON loading, saving, and duplicate-key scan
src/main/java/com/skanga/jsoneditor/model    JSON document model
src/main/java/com/skanga/jsoneditor/util     Shared utilities and message access
src/main/resources/bundles                   Localized UI strings
src/test/java/com/skanga/jsoneditor          Unit and UI behavior tests

The data/ directory is intentionally ignored and is not part of the repository.

Duplicate Key Handling

JSON object keys are expected to be unique, but real files sometimes contain duplicates:

{
  "role": "user",
  "role": "admin"
}

The editor uses Gson for normal JSON loading, which keeps the last value for a duplicated key. To avoid silently hiding that behavior, JSON Editor also runs a lazy duplicate-key scan after the file is loaded.

When duplicates are found, the editor shows a warning panel at the top of the detail view:

WARNING: Duplicate JSON keys detected. The editor loaded the last value for each duplicate key. Saving the JSON file will delete all the duplicate values. The first duplicate is: /path/to/key

The warning can be dismissed after review. If you try to save a file that originally contained duplicate keys, the editor asks for confirmation because saving rewrites the JSON and removes earlier duplicate values.

Releases

Published releases are available on GitHub:

https://github.com/skanga/json-editor/releases

For local release builds:

mvn clean package

The runnable shaded JAR is written to a stable local path:

target/json-editor.jar

Release tags and uploaded JAR asset names are derived from pom.xml by scripts/release.py:

python scripts/release.py

See CHANGELOG.md for release notes.

License

MIT. See LICENSE.