Markdown Link Reference Definitions
Last updated: 2026-10-14
Link Reference Definitions CommonMark core
Define [id]: url once, reference it as [text][id] anywhere. Same URL reused cleanly; one line to swap it. The engineered choice for long docs — definitions render nothing.
| Group | Edge Cases & Rules |
|---|---|
| Spec level | CommonMark core |
| Spec version | CommonMark 0.31.2 + GFM |
📝 Syntax
[text][id]
[id]: https://example.com▶ Live Example
Edit Markdown on the left, see the result on the right
💡 Key points
ℹ️ Note Definitions may sit anywhere (traditionally the end) and render nothing.
💡 Tip Implicit references [text][] reuse the text as the id — zero extra naming.
❓ FAQ
Q Can an id be defined twice?
A The first definition wins; duplicates are ignored.
Q Are ids case-sensitive?
A No — [GH] and [gh] match the same definition.
Q Can definitions sit inside lists or quotes?
A Yes, and their scope is the whole document, not the enclosing block.
📚 See also
LinksCommonMark core ImagesCommonMark core