LineLengthOptimal [rule] v1.0.0

Body text containers (paragraphs, list items, block quotes) MUST limit measure (line length) to between 45 and 75 characters per line. This range is the documented optimum for sustained reading — below 45ch the eye breaks rhythm, above 75ch it loses the next-line return.

Checks

• @community/check-line-length-optimal

Applies To

@community/type-html-artifact

Severity

medium

Severity Combination

body block measure > 90ch                  → BLOCK  (definitely fatiguing)
body block measure 75–90ch or 35–45ch      → WARN
body block measure 45–75ch                 → PASS

Failure Mode

Readers fatigue, abandon, or stop returning. Lines longer than 75ch produce 'reading drift' where the eye skips lines; lines shorter than 45ch produce too many returns and break comprehension.

Remediation

• Add max-width: 65ch to the body-copy container (e.g. .prose, <article> p).
• For multi-column layouts, set column width via column-width: 30ch rather than fixed pixel grids.
• If the page is full-bleed by design, restrict only the long-form content while letting media (images, code blocks) extend wider.

Exceptions

• • Case: Code blocks
  • Allowed When: Source code commonly extends past 80ch and is read line-by-line; horizontal scroll is acceptable.
• • Case: Tabular data
  • Allowed When: Tables are scanned, not read linearly; column count drives width.
• • Case: CJK languages
  • Allowed When: Chinese / Japanese / Korean prefer ~30–40 full-width characters per line; the 45–75 range is for Latin script.

LineLengthOptimal [rule] v1.0.0

Body text containers (paragraphs, list items, block quotes) MUST limit measure (line length) to between 45 and 75 characters per line. This range is the documented optimum for sustained reading — below 45ch the eye breaks rhythm, above 75ch it loses the next-line return.

Checks

• @community/check-line-length-optimal

Applies To

@community/type-html-artifact

Severity

medium

Severity Combination

body block measure > 90ch                  → BLOCK  (definitely fatiguing)
body block measure 75–90ch or 35–45ch      → WARN
body block measure 45–75ch                 → PASS

Failure Mode

Readers fatigue, abandon, or stop returning. Lines longer than 75ch produce 'reading drift' where the eye skips lines; lines shorter than 45ch produce too many returns and break comprehension.

Remediation

• Add max-width: 65ch to the body-copy container (e.g. .prose, <article> p).
• For multi-column layouts, set column width via column-width: 30ch rather than fixed pixel grids.
• If the page is full-bleed by design, restrict only the long-form content while letting media (images, code blocks) extend wider.

Exceptions

• • Case: Code blocks
  • Allowed When: Source code commonly extends past 80ch and is read line-by-line; horizontal scroll is acceptable.
• • Case: Tabular data
  • Allowed When: Tables are scanned, not read linearly; column count drives width.
• • Case: CJK languages
  • Allowed When: Chinese / Japanese / Korean prefer ~30–40 full-width characters per line; the 45–75 range is for Latin script.

Applies To

@community/type-html-artifact

Severity

medium

Validates With

• @community/fact-optimal-line-length

Severity Combination

body block measure > 90ch                  → BLOCK  (definitely fatiguing)
body block measure 75–90ch or 35–45ch      → WARN
body block measure 45–75ch                 → PASS

Failure Mode

Readers fatigue, abandon, or stop returning. Lines longer than 75ch produce 'reading drift' where the eye skips lines; lines shorter than 45ch produce too many returns and break comprehension.

Remediation

• Add max-width: 65ch to the body-copy container (e.g. .prose, <article> p).
• For multi-column layouts, set column width via column-width: 30ch rather than fixed pixel grids.
• If the page is full-bleed by design, restrict only the long-form content while letting media (images, code blocks) extend wider.

Exceptions

• • Case: Code blocks
  • Allowed When: Source code commonly extends past 80ch and is read line-by-line; horizontal scroll is acceptable.
• • Case: Tabular data
  • Allowed When: Tables are scanned, not read linearly; column count drives width.
• • Case: CJK languages
  • Allowed When: Chinese / Japanese / Korean prefer ~30–40 full-width characters per line; the 45–75 range is for Latin script.

See Also

• @community/check-line-length-optimal