Markdown Spaces & Tabs
Last updated: 2026-10-14
Spaces & Tabs CommonMark core
Markdown expands tabs at 4-column tab stops before computing indentation; mixing tabs and spaces invites bugs — 3 spaces plus a tab can equal 7. Standardize on spaces to kill a whole bug class.
| Group | Edge Cases & Rules |
|---|---|
| Spec level | CommonMark core |
| Spec version | CommonMark 0.31.2 + GFM |
📝 Syntax
(a tab = expanded to a 4-column tab stop)▶ Live Example
Edit Markdown on the left, see the result on the right
💡 Key points
⚠️ Warning The indented-code threshold is 4 spaces; mixed indentation can silently turn prose into code.
💡 Tip Set indent_style = space for *.md in .editorconfig once and forget it.
❓ FAQ
Q How wide is a tab exactly?
A Expanded to the next multiple of 4 columns — not a flat 4 spaces.
Q Why did my list item become code?
A Its indentation hit 4+ spaces after tab expansion, becoming an indented code block.
Q How do editors help?
A Show whitespace and convert tabs to spaces on save — visible immediately.
📚 See also
Indented Code BlocksCommonMark core List NestingCommonMark core