Markdown balances readability and structure. Headings, lists, links, footnotes, and code blocks require no proprietary renderer to make sense. When an application improves or disappears, you still open the files, edit with any text editor, and convert with pandoc as needed. Even broken plugins cannot corrupt a simple asterisk or hash mark that any future program can parse.
Store tags, aliases, created dates, or project links in YAML front matter at the top of a file, where parsers and humans can see it. Because it is text, you can batch-edit across hundreds of notes, or programmatically generate indices. No database dumps, no opaque blobs, just transparent key‑value pairs that travel across tools without permission slips or brittle, one-off bridging scripts.
When structure matters, formats like OPML, CSV, and JSON bridge editors with minimal friction. Outlines can move between mind mappers and text editors. Tables export cleanly to spreadsheets for analysis. Because the spec is public, you can validate, transform, and repair files yourself. Interoperability is not a favor granted by vendors; it is a property of choosing well-documented containers.