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Rule - MD020#

Property Value
Aliases md020, no-missing-space-closed-atx
Autofix Available No
Enabled By Default Yes

Summary#

Ensure at least one space exists between hash marks and text in Atx Closed Headings.

Reasoning#

Scope Boundary: This rule checks closed-style headings only. Rule MD018 checks open-style headings. A heading is "open" if it does not end with one or more hash characters (e.g., # Heading).

Correctness#

Missing spaces between hash marks and heading text in Atx Closed Headings can make headings harder to read and may confuse parsers. Consistent spacing improves both readability and document correctness.

Examples#

Failure Scenarios#

This rule triggers when there is no space between the opening hash marks and the heading text in an Atx Closed Heading.

#Heading 1 #

Explanation: This example violates the rule because there is no space between the opening # and the heading text Heading 1. An Atx Closed Heading requires at least one space after the opening hash marks.

Unlike the previous example, this case has a space after the opening hash but no space before the closing hash.

# Heading 1#

Explanation: This example violates the rule because there is no space between the heading text Heading 1 and the closing #. An Atx Closed Heading requires at least one space before the closing hash marks.

This case lacks spaces on both sides of the heading text.

#Heading 1#

Explanation: This example violates the rule because there are no spaces between the hash marks and the heading text Heading 1. An Atx Closed Heading requires at least one space after the opening hash marks and before the closing hash marks.

Correct Scenarios#

This rule does not trigger when there are 1 or more spaces on either side of the Atx Closed Heading:

## Heading 2 ##

Explanation: This example satisfies the rule because there is at least one space after the opening ## and before the closing ##. The heading text Heading 2 is properly padded.

Unlike the previous example, this case lacks a closing hash character entirely, which places it outside the scope of this rule.

#Heading1

Explanation: The line #Heading1 is an Atx Open Heading, not a Closed Heading. Since this rule only targets Atx Closed Headings, this rule does not trigger. The spacing for open headings is governed by Rule MD018.

Fix Description#

The reason for not being able to auto-fix this rule is context. As stated above, the rule looks for:

No space present inside of the hashes on a possible Atx Closed Heading.

As there is only a possibility that the Markdown:

#Heading 1#

represents a heading, there is a lack of context surrounding the implied meaning of that block of text. It is better for this rule to trigger and have the author of the document clarify the context than to assume that the above text will always indicate a heading.

Configuration#

Prefixes
plugins.md020.
plugins.no-missing-space-closed-atx.
Value Name Type Default Description
enabled boolean True Whether the Rule Plugin is enabled.

Origination of Rule#

This rule is largely inspired by the MarkdownLint rule MD020.

Differences From MarkdownLint Rule#

Like the PyMarkdown version of Rule MD018, the original version of this rule did not trigger in Block Quote elements or List elements but did fire within Setext Heading elements. These changes were also made to this rule to keep it consistent with Rule MD018.