Rule - MD013

Property	Value
Aliases	md013, line-length
Autofix Available	Yes
Enabled By Default	Yes

Summary

Line length.

Reasoning

Readability/Consistency

For every user, there is a specific number of columns that can be displayed on their screen before the user feels that data on their screen becomes unreadable. To provide consistency across application or organizations, a specific maximum line length may be put in place to establish an expectation of console window and editor window width. That established line length, used across a set of documents, helps to promote a consistent line length, setting expectations in the reader's mind that improve the readability of those documents.

Examples

Failure Scenarios

This rule triggers if the length of any line exceeds a given character count. Assuming that the configuration values are set to a maximum line length of 50 characters, the following example will trigger this rule:

Markdown This is a sample line that is a total of 60 characters long.

Correct Scenarios

This rule does not trigger if the length of any line is less than or equal to a given character count. If the configuration values are set to a maximum line length of 50 characters, the following example will not trigger this rule:

Markdown This is a sample line that is 50 characters long.

Long Last Words

To allow for longer, continuous constructs, such as URLs, a check is performed to see if there is any whitespace beyond the specified character count. If there are no whitespace characters, then this rule will not trigger. An example of this is:

Markdown This is a sample line that is a total of 60-characters-long.

where the boundary is at the second c character in 60-characters-long.

If this is not the desired behavior, there are two options. The first option, the strict configuration value, forces this rule to trigger if any character is present past the specified line length. The stern configuration is another option, allowing lines without any spaces past the specified line length while triggering on lines that are too long.

Special Elements

For line lengths, two types of elements stick out as needing special attention: headings and code blocks. To that extent, the heading_line_length configuration value specifies the line length for headings and headings configuration value specifies whether this rule triggers at all for headings. Similarly, the code_block_line_length and code_blocks configuration values perform the same action for code blocks.

Fix Description

The auto-fix feature for this rule is scheduled to be added soon after the v1.0.0 release.

Configuration

Prefixes
plugins.md013.
plugins.line-length.

Value Name	Type	Default	Description
enabled	boolean	True	Whether the Rule Plugin is enabled.
line_length	integer	80	Maximum number of characters on a normal line.
heading_line_length	integer	80	Maximum number of characters on a heading line.
code_block_line_length	integer	80	Maximum number of characters on a code block line.
headings	boolean	True	Whether the Rule Plugin triggers on lines in a heading.
code_blocks	boolean	True	Whether the Rule Plugin triggers on lines in a code block.
stern	boolean	False	Whether the 'stern' trigger rules are in effect.
strict	boolean	False	Whether the 'strict' trigger rules are in effect.

Origination of Rule

This rule is largely inspired by the MarkdownLint rule MD013.

Differences From MarkdownLint Rule

The substantial difference from the original rule is that the table configuration value is not present as the PyMarkdown parser does not currently support tables.