MDS001: line-length

Line exceeds maximum length.

# Settings

Valid exclude values:

• code-blocks – skip lines inside fenced or indented code blocks
• tables – skip lines that are table rows (starting with |)
• urls – skip lines whose only content is a URL

Set exclude: [] to check everything (equivalent to the old strict: true).

The strict setting is deprecated. If present, strict: true is translated to exclude: [] and strict: false to the default exclude list.

# Per-category limits

When heading-max is set, heading lines (ATX and Setext) use that limit instead of max. When code-block-max is set, lines inside fenced or indented code blocks use that limit instead of max. When either setting is unset (absent), lines of that type inherit max.

Per-category limits and exclude compose. A code block line excluded via exclude: [code-blocks] is still skipped, even when code-block-max is set.

# Stern mode

When stern: true, a line that exceeds the active limit is flagged only if it contains a space character at or beyond the limit column. Lines with no space past the limit (for example a long URL at the end of a line) are allowed.

Stern mode applies independently of exclude. A line inside a code block that is excluded via exclude: [code-blocks] is still skipped regardless of stern. Stern uses the active max for each line type, so it respects heading-max and code-block-max when set.

# Reflow (auto-fix)

By default the rule reports long lines but does not rewrite them: mdsmith fix leaves prose untouched. Set reflow: true to opt into the auto-fix, which rewraps over-long top-level prose paragraphs so every line fits within max.

Reflow is deliberately conservative. It rewraps only paragraphs that sit directly in the document body and contain a flagged long line. It skips headings, list items, block quotes, tables, generated sections, paragraphs that carry a Markdown hard line break, and paragraphs that contain inline raw HTML. Inline code spans are preserved verbatim, and a single word wider than max (a long URL or link) keeps its own over-long line rather than being broken.

Wrapping is abbreviation-aware. It never ends a wrapped line on an abbreviation, and it never splits a run of initials. So e.g. stays with the word it introduces, and J. R. R. Tolkien is never broken across lines. Detection reuses mdsmith’s trained abbreviation model — the same one the readability rules use to split sentences. It recognises honorifics (Dr., Mr.), reference forms (vs., No.), initials (J.), and dotted forms (e.g., i.e., U.S.A.). The abbreviations setting adds project-specific entries the model does not know (etc., approx.), and append-merges across config layers so a kind can extend the inherited list without restating it.

The payoff is clearest at the wrap boundary. A naive word wrap of this line at 80 columns splits the spaced acronym across the break:

Historians traced the founding and the early constitutional debates of the U. S.
A. with real care.

Reflow breaks before the acronym instead, keeping U. S. A. whole on one line:

Historians traced the founding and the early constitutional debates of the
U. S. A. with real care.

# Config

Enable (default):

rules:
  line-length:
    max: 80
    exclude:
      - code-blocks
      - tables
      - urls

Disable:

rules:
  line-length: false

Custom (per-category limits):

rules:
  line-length:
    max: 80
    heading-max: 100
    code-block-max: 120
    exclude:
      - tables
      - urls

Custom (stern mode; allow long lines without spaces past the limit):

rules:
  line-length:
    max: 80
    stern: true

Custom (check everything; no exclusions):

rules:
  line-length:
    max: 80
    exclude: []

Custom (enable the reflow auto-fix and add project abbreviations):

rules:
  line-length:
    max: 80
    reflow: true
    abbreviations:
      - etc.
      - approx.

Custom (skip only code blocks and URLs; check tables):

rules:
  line-length:
    max: 120
    exclude:
      - code-blocks
      - urls

# Examples

# Bad

Line exceeds the default 80-character limit:

# Title

This line is deliberately made to exceed the eighty character limit by adding extra words here now.

Line exceeds a custom max: 120 limit:

# Title

This line is deliberately made very long so that it exceeds the one hundred and twenty character limit set right here!!!!

Heading exceeds heading-max: 60:

# This heading is deliberately made long enough to exceed sixty chars

Long line with spaces past the limit (stern: true still flags it):

# Title

This line is deliberately made to exceed the eighty character limit by adding extra words here now.

No exclusions — URLs and code blocks are also checked:

# Title

This line is deliberately made to exceed the eighty character limit by adding extra words here now.

https://example.com/this-is-a-very-long-url-that-exceeds-eighty-characters-and-should-be-flagged

# Good

# Title

This line is well within the eighty character limit.

Heading within heading-max: 100 (even though it exceeds max: 80):

# This heading is within the heading-max limit of one hundred characters

Code block within code-block-max: 120:

# Title

```text
This line inside a code block is over 80 characters but within the code-block-max limit of one hundred and twenty.
```

# Meta-Information

• ID: MDS001
• Name: line-length
• Status: ready
• Default: enabled, max: 80
• Fixable: yes (opt-in via reflow)
• Implementation: source
• Category: line
• markdownlint: MD013 (line-length)
• rumdl: MD013 (line-length)
• mado: MD013 (line-length)
• gomarklint: max-line-length