Filenames and file types

Naming guidelines

Make file and directory names lowercase. In general, separate words with hyphens, not underscores. Use only standard ASCII alphanumeric characters in file and directory names.

Exceptions for consistency

If you're adding to a directory where everything else already uses underscores, and it's not feasible to change everything to hyphens, it's okay to use underscores to stay consistent.

For example, if the directory already has lesson_1.jd, lesson_2.jd, and lesson_3.jd, it's okay to add your new file as lesson_4.jd instead of lesson-4.jd. However, in all other situations, use hyphens.

Recommended: avoiding-cliches.jd

Sometimes OK: avoiding_cliches.jd

Not recommended: avoidingcliches.jd, avoidingCliches.jd, avoiding-clichés.jd

Other exceptions

It's okay to have some inconsistency in filenames if it can't otherwise be avoided. For example, sometimes tools that generate reference documentation produce file names based on different style requirements or based on the design and naming conventions of the product or API itself. In those cases, it's okay to make exceptions for those files.

Referring to file types

When you're discussing a file type, use the formal name of the type. (The file type name is often in all caps, because many file type names are acronyms or initialisms.) Do not use the filename extension to refer generically to the file type.

Recommended: a PNG file

Not recommended: a .png file

Recommended: a Bash file

Not recommended: an .sh file

The following table lists examples of filename extensions and the corresponding file type names to use.

Extension File type name
.csv CSV file
.exe executable file
.gif GIF file
.img disk image file
.jpg, .jpeg JPEG file
.json JSON file
.pdf PDF file
.png PNG file
.ps PowerShell file
.py Python file
.sh Bash file
.sql SQL file
.svg SVG file
.tar tar file
.txt text file
.yaml YAML file
.zip zip file

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Google Developer Documentation Style Guide
Google Developer Documentation Style Guide