CommonMark or GitHub-flavored?

Both. CommonMark is the baseline; GFM extensions (tables, task lists, strikethrough, autolinks) are marked as GFM-specific.

Does it cover footnotes?

Yes — GFM footnote syntax. Plus the fallback for Markdown flavors that don't support them.

Allowed inline. The cheatsheet notes when HTML is preserved (most renderers) vs stripped (some strict flavors).

Covered — colons in the separator row set alignment (left :---, center :---:, right ---:). Works in all table-supporting flavors.

CommonMark + GitHub-flavored Markdown syntax at a glance. Part of the DevTools Surf developer suite. Browse more tools in the Cheatsheets collection.

Markdown was created by John Gruber with contributions from Aaron Swartz and published on March 19, 2004, as a plain-text formatting syntax.
CommonMark, an effort to standardize Markdown, launched in 2014 after years of inconsistencies between Markdown implementations — GitHub adopted it in 2017.
GitHub Flavored Markdown (GFM) added tables, task lists, and strikethrough to the original spec, and processes over 200 million Markdown files in repositories.

CommonMark or GitHub-flavored?: Both. CommonMark is the baseline; GFM extensions (tables, task lists, strikethrough, autolinks) are marked as GFM-specific.
Does it cover footnotes?: Yes — GFM footnote syntax. Plus the fallback for Markdown flavors that don't support them.
What about HTML inside Markdown?: Allowed inline. The cheatsheet notes when HTML is preserved (most renderers) vs stripped (some strict flavors).
Tables — how do I align columns?: Covered — colons in the separator row set alignment (left :---, center :---:, right ---:). Works in all table-supporting flavors.

CommonMark + GitHub-flavored Markdown syntax at a glance. Part of the DevTools Surf developer suite. Browse more tools in the Cheatsheets collection.

Markdown was created by John Gruber with contributions from Aaron Swartz and published on March 19, 2004, as a plain-text formatting syntax.
CommonMark, an effort to standardize Markdown, launched in 2014 after years of inconsistencies between Markdown implementations — GitHub adopted it in 2017.
GitHub Flavored Markdown (GFM) added tables, task lists, and strikethrough to the original spec, and processes over 200 million Markdown files in repositories.

CommonMark or GitHub-flavored?: Both. CommonMark is the baseline; GFM extensions (tables, task lists, strikethrough, autolinks) are marked as GFM-specific.
Does it cover footnotes?: Yes — GFM footnote syntax. Plus the fallback for Markdown flavors that don't support them.
What about HTML inside Markdown?: Allowed inline. The cheatsheet notes when HTML is preserved (most renderers) vs stripped (some strict flavors).
Tables — how do I align columns?: Covered — colons in the separator row set alignment (left :---, center :---:, right ---:). Works in all table-supporting flavors.