How to Learn the Common File Extensions
The letters after the dot in a filename — .pdf, .png, .js — tell you what kind of file it is and which program opens it. Knowing the common extensions makes you far more capable with computers. This deck teaches the ones you meet every day.
There are 14 cards in the deck below. You can read through them, practise them right here with the flip-card player, and then save the deck to study properly with spaced repetition — the method that makes them stick for months, not minutes.
Why the common file extensions is hard to memorize (and the fix)
Some are obvious (.mp3 = music) but others are easily confused (.jpg vs .png for images, .doc vs .pdf for documents). Knowing what each is for prevents mistakes.
The fix is active recall plus spaced repetition. Instead of re-reading the list (which feels productive but barely works), you test yourself — pull each answer out of memory — and you review each card on a schedule that stretches over time. Every time you successfully recall a fact, the memory gets stronger and the next review is pushed further out. That's how you go from "I saw it once" to "I just know it."
The fastest way to learn the common file extensions
- Break it into small batches. Learn them by group — web files, images, documents, media, archives — a handful at a time.
- Test, don't re-read. Look at the question, say the answer out loud before flipping the card. The little struggle to recall is what builds the memory — a smooth re-read does almost nothing.
- Review on a schedule. Spaced repetition shows you each card right before you'd forget it. Get one right and it comes back in a few days, then a week, then a month. Miss one and it comes back sooner.
- Keep sessions short and daily. Five to ten minutes a day beats a two-hour cram every time. Consistency is the whole game.
One fact per card. The extension tells the computer which program to use — changing it does not actually convert the file.
The full deck: the Common File Extensions
Here's every card in the set. Practise them above, or save the deck and let spaced repetition schedule your reviews automatically.
| Extension | File type |
|---|---|
| What is a .html file? | A web page (HyperText Markup Language) |
| What is a .css file? | A stylesheet (Cascading Style Sheets) |
| What is a .js file? | A JavaScript program |
| What is a .py file? | A Python program |
| What is a .pdf file? | A Portable Document Format file (fixed layout) |
| What is a .png file? | An image with transparency support |
| What is a .jpg / .jpeg file? | A compressed photo image |
| What is a .gif file? | An image that can be animated |
| What is a .mp3 file? | A compressed audio (music) file |
| What is a .mp4 file? | A compressed video file |
| What is a .zip file? | A compressed archive of one or more files |
| What is a .csv file? | Comma-Separated Values — a simple spreadsheet/table |
| What is a .json file? | JavaScript Object Notation — a data format |
| What is a .txt file? | A plain text file |
Save this deck and actually remember it
Create a free account, keep this 14-card deck, and we'll schedule every review at the perfect moment. First deck free forever — no credit card.
Study this deck free →FAQ: learning the common file extensions
How long does it take to learn the common file extensions?
Most people can lock in the common file extensions within one to three weeks of short daily sessions. With spaced repetition doing 10–14 cards a day, you'll recognise them within days and recall them reliably within a couple of weeks.
What's the best way to memorize the common file extensions?
Active recall plus spaced repetition. Test yourself instead of re-reading, and review on a schedule that spaces the cards out over time. Flashcards are built for exactly this — which is why the deck above is the fastest path.
Is this deck free?
Yes. You can practise all 14 cards on this page for free with no account. Sign up (also free) to save the deck and let spaced repetition schedule your reviews so it sticks long-term.