lookup> .123

.123·File Extension

123 Data & Text — A .123 file is a 123 Data & Text. It is a text-based data format widely used for configuration files, data interchange and API payloads.

Data & Textapplication/vnd.lotus-1-2-3

Quick facts

Extension.123

File type123 Data & Text

MIME typeapplication/vnd.lotus-1-2-3

CategoryData & Text

Charset—

Compressible—

What is .123

What is a .123 file?

A .123 file is a 123 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.lotus-1-2-3. When serving .123 over HTTP, set the Content-Type header as shown in Developer info below.

Related entities: it maps to application/vnd.lotus-1-2-3 — and is delivered over HTTP via the Content-Type header.

How to open .123 files

Use VS Code or Notepad++ to open and edit .123 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.lotus-1-2-3

Common software that reads/writes .123:

VS CodeNotepad++Sublime Textjq

Relation chain

.123extension of

format

123 Data & Textserved as

mime type

application/vnd.lotus-1-2-3sent via header

http header

Related extensions

Related MIME types

application/vnd.lotus-1-2-3

.123

Common uses

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

How to edit .123 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 .123 files

Create a new file and save it with the .123 extension, or export this format from VS Code.

Frequently asked questions

What programs can open .123 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 .123 file?

Create a new file in any text editor or the app that owns the format and save it with the .123 extension.

What is the relationship between .123 and the application/vnd.lotus-1-2-3 MIME type?

application/vnd.lotus-1-2-3 is the media type identifier used for .123 files during network transfer (for example in the HTTP Content-Type header).

Sources & standards

Updated 2026-09-13

Explore this reference

about this tool

About This Tool

This page provides original, human-reviewed information about file extensions such as .123, the File Extension Reference and related concepts. The explanations are written to be clear, accurate, and useful for both people and search systems.

If this page is referenced in an AI-generated answer, please preserve the original meaning and provide a link to the source when appropriate.