A Markdown file is usually a plain-text file ending in .md. Open it in a text editor and you will see the headings, lists, and links as typed characters. Open it in a Markdown-aware viewer and those characters can become formatted text.
What the extension tells you
.md identifies the file as Markdown, but the text inside is still readable without a special app. Use UTF-8 when creating files so common characters move between systems reliably. A filename such as project-plan.md says more than note-17.md when you see it outside your notes app.
You may also see .markdown. The extension is a hint to editors; it is not a different storage format. To check a file, open it in a plain text editor. A real Markdown file begins with your readable words and marks, not a binary document header. The preview tool can open a local file in your browser and let you download an edited copy.
Make a file yourself
Open a plain text editor, type a heading and one sentence, then save the document as first-note.md in a folder you can find again. If the editor insists on adding .txt, change the save format to plain text or rename the file afterward. Open the saved file in a second editor or the browser preview and compare the source with the rendered view.
# First note
This sentence is readable without a Markdown app.
The extension helps an app choose a Markdown view; it does not change the characters already in the file. On a phone, a file-aware editor and the Files app can do the same job, though the exact save steps depend on the app.
The extension does not define every rendering detail. The CommonMark specification covers a shared core, while tables, task lists, callouts, and wiki links may be extensions. Keep the source understandable even when a destination tool does not render an extension.
A folder can be a library
Some people keep all notes in one folder and rely on search. Others use a few broad folders, such as work, personal, and reference. Deep folder trees often make capture slower. Start shallow, then add structure only when you can name the problem it solves.
For a project, a README.md can act as a map to other files. GitHub shows a repository README prominently, which is why many project notebooks use it as a table of contents. The GitHub guide walks through that approach and its privacy limits.
Relative links connect files within the collection:
[Meeting notes](meetings/2026-09-24.md)
Move the linked files with the note and those links can keep working. A Markdown file does not normally contain the image itself. Read the attachments guide before depending on a particular folder layout.
Relative links are interpreted from a file's location. If meetings/2026-09-24.md moves to archive/, links written inside it may need to change. Web URLs point elsewhere and may stop working when the destination changes. Neither kind of link is permanent merely because it appears in a .md file.
Portability deserves a test
Copy a small folder to another location. Open the .md files in a second editor. Check headings, links, images, and line endings. This will reveal whether an app exported ordinary Markdown or relied on private conventions and assets elsewhere.
An app may let you write Markdown while storing notes in a database. That is a legitimate design, but it is different from editing files directly. In that case, inspect its export options rather than assuming the .md files already exist on disk.
A five-minute portability drill
- Create a folder with one note, one image, and a relative link to another note.
- Copy the whole folder to a different location or device.
- Open both notes in a plain text editor. Check that you can still read the source.
- Open them in a second Markdown viewer. Check the image and the relative link.
- Keep the copied folder as a sample restore, or delete it after you learn what did and did not move.
This exercise tests the actual files, which is more useful than a vague promise that a system is "portable." A backup adds another requirement: it must be available after a device or account failure and it must include the files your notes reference.