# File extensions: the ending of a filename

[Concepts explained](README.md)

A **file extension** is the final part of a filename, usually after its last dot. In `quiz.pliro`, the extension is `.pliro`. It gives people and programs a clue about the file's purpose.

## Names you will meet

| Extension | Usual purpose here |
| --- | --- |
| `.pliro` | Pliro source code |
| `.bipli` | A portable Pliro project bundle |
| `.md` | Markdown documentation, such as this article |
| `.json` | Structured text data |
| `.png` | An image |
| `.exe` | A Windows executable application |

The **file format** is the actual set of rules for the contents. An extension is a label. Renaming `drawing.png` to `drawing.pliro` does not turn its picture data into source code, just as writing “juice” on a water bottle does not change the drink.

## Source and finished app

A `.pliro` file can be read as text. Building a program creates an application containing machine instructions and its needed runtime support. Renaming the source to `.exe` does not perform that build.

A `.bipli` project can hold several source files, a manifest, and assets. It is more than a single source file with a different name.

## Watch the whole name

Some file browsers hide familiar extensions. A file that looks like `quiz.pliro` might actually be named `quiz.pliro.txt`. If Pliro cannot recognize a file, inspect its full name. The extension alone also cannot prove that a downloaded file is safe.

[Source files](../syntax/source-files.md) · [Compilers](compiler-and-interpreter.md)