lookup> .c4u

.C4U·File Extension

C4U Data & Text — A .c4u file is a C4U Data & Text. It is a text-based data format widely used for configuration files, data interchange and API payloads.

Data & Textapplication/vnd.clonk.c4group

Quick facts

Extension.c4u

File typeC4U Data & Text

MIME typeapplication/vnd.clonk.c4group

CategoryData & Text

Charset—

Compressible—

What is .c4u

What is a .c4u file?

A .c4u file is a C4U Data & Text. It is a text-based data format widely used for configuration files, data interchange and API payloads.

In the mime-db registry it maps to application/vnd.clonk.c4group. When serving .c4u over HTTP, set the Content-Type header as shown in Developer info below.

Related entities: it maps to application/vnd.clonk.c4group — and is delivered over HTTP via the Content-Type header.

How to open .c4u files

Use VS Code or Notepad++ to open and edit .c4u files.
Any text editor (Notepad, VS Code) can inspect the raw content as text.

Developer info

When served over HTTP, responses should set the following header:

Content-Type: application/vnd.clonk.c4group

Common software that reads/writes .c4u:

VS CodeNotepad++Sublime Textjq

Relation chain

.c4uextension of

format

C4U Data & Textserved as

mime type

application/vnd.clonk.c4groupsent via header

http header

Related extensions

Related MIME types

application/vnd.clonk.c4group

.c4g .c4d .c4f

Common uses

Configuration files
Data interchange between systems
API request and response payloads
Logs and data exports

How to edit .c4u files

Open the file with VS Code, make your changes and save.
Most editors preserve the original formatting and encoding — avoid changing the charset.

How to create .c4u files

Create a new file and save it with the .c4u extension, or export this format from VS Code.

Frequently asked questions

What programs can open .c4u files?

Common options include VS Code, Notepad++, Sublime Text. You can also open many of these files with built-in viewers or a browser.

How do I create a .c4u file?

Create a new file in any text editor or the app that owns the format and save it with the .c4u extension.

What is the relationship between .c4u and the application/vnd.clonk.c4group MIME type?

application/vnd.clonk.c4group is the media type identifier used for .c4u files during network transfer (for example in the HTTP Content-Type header).

Sources & standards

Updated 2026-09-13

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