What is the UI4JD file format?
A .ui4jd file is a configuration file that belongs to Project 4JD UI, a resource pack for Minecraft Bedrock Edition made by CrisXolt. The pack rebuilds the game's menus to look like the old "Legacy Console" interface that 4J Studios designed for the Xbox and PlayStation editions. Each file contains JSON-UI markup: a namespace declaration followed by definitions for interface pieces such as durability bars, panels, tabs, and buttons, along with the textures bound to them.
The content is JSON, but it follows Minecraft's JSON-UI dialect, which permits C-style /* */ comments. Because of those comments, a strict JSON validator may flag the file even though the data is valid for the game. In the project's source tree these files sit inside a ui4jd folder, which is where the extension gets its name.
Security & safety
RISK: LOWA .ui4jd file is plain-text JSON with no executable code, so opening it in a text editor is safe. The only caution is the pack itself: it is distributed as a ZIP renamed to .mcpack, so download it from the project's official source rather than untrusted mirrors.
Format details
in a nutshell- 4th Dimension (4D) database - 4D is a database and application development environment, but it does not use the
.ui4jdextension; the '4JD' here is unrelated and refers to 4J Studios. - ui4j (Java library) - A Java web-automation library named ui4j exists on GitHub; it is a codebase, not a file format, and has no connection to
.ui4jdfiles.
Programs that open UI4JD files
Windows3 apps
Notepad
Open-source Open the file as plain text; use JSON syntax coloring to inspect the UI definitions. 
Visual Studio Code
Free Open the .ui4jd file to read and edit the JSON-UI markup with syntax highlighting and bracket matching. 
Minecraft Bedrock Edition (Project 4JD UI pack)
Paid Import the Project 4JD UI .mcpack and apply it as a resource pack so the game loads the UI these files define. 
macOS2 apps
Linux2 apps
Technical details
deep spec| Encoding | UTF-8 text |
| Container | None (plain text) |
| Compression | None (individual files); distributed inside a ZIP-based .mcpack archive |
| Typical size | A few KB to tens of KB per file |
| Structure | A single JSON object opened with a namespace key, followed by named UI element definitions (type, size, texture bindings). Uses Minecraft Bedrock JSON-UI syntax and allows C-style /* */ comments, which strict JSON parsers reject. |
| Platforms | Windows, macOS, Linux |
| Notes | Functionally identical to Minecraft Bedrock .json JSON-UI files. The custom .ui4jd extension is used by the Project 4JD UI resource pack to group its UI override files inside a ui4jd directory. Minecraft itself reads UI definitions from .json files, so these are project-internal source files rather than a format the game loads directly. |
| Released | 2023 |
| Specification | github.com |
UI4JD conversions
Community Q&A
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Frequently asked questions
What is a UI4JD file?
How do I open a UI4JD file?
Is UI4JD the same as JSON?
Can Minecraft read .ui4jd files directly?
.json files. The .ui4jd extension is a naming choice used by the Project 4JD UI project to organize its source files.How do I install the Project 4JD UI pack?
.mcpack extension, then open it so Minecraft Bedrock imports it as a resource pack.
