INI

INI is a simple plain text format used for software configuration. The name is commonly understood to stand for initialization file, and the format was popular on early Windows systems, where configuration data was stored in files with the .ini extension such as system.ini and win.ini. INI files are still used by some applications and increasingly replaced by other formats, but remain in use in many cross-platform projects and tools.

The typical INI structure consists of sections and key-value pairs. Sections are indicated by a name enclosed in square brackets, for example [Display]. Within a section, lines in the form key=value assign values to options. Comments are usually introduced with a semicolon or a hash character. Whitespace around keys and values is generally ignored by parsers, and values are treated as strings. Many implementations also allow empty values, and some variants support multiline values or alternative separators such as a colon, but the equals sign is the most common.

Because there is no universal standard for INI, behavior varies by parser. In Windows, the API functions GetPrivateProfileString and WritePrivateProfileString provide a legacy mechanism to read and write INI data, treating keys and sections as case-insensitive. Across platforms, libraries exist in numerous languages to read and write INI files, with differing rules for case sensitivity, encoding, and continuation lines. INI remains valued for simple, human-readable configuration but is often supplanted by more expressive formats such as JSON, YAML, or TOML for complex data.