Expert on the history, origin, and correct use of the em dash.
SkillScore91Maintained
Automatic
◆Writing & Editing pack
Last verified 8/2/2026
What it changes
Passed 20 of 22 test cases with the skill, and 12 of 22 without it.
Without skill55%
With skill91%
Checks it passed that the model alone missed
Replaces em dash with ASCII hyphen.
Uses ASCII hyphens instead of em dashes.
Replaces em dash characters with hyphens.
and 6 more in the full report
9 fixed11 passed either way1 still failing1 broke
Pass-rate lift
+36 pp
Tokens
+137%
Agent turns
0%
Response time
-45%
Model gemini-3.6-flashMeasured 8/2/2026v120 of 22 cases passed with skill
Tokens, turns and time describe resource use, not a dollar price.
See it in action
One of 9 test cases the skill fixed. Same model, same prompt, with and without the skill.
1 of 9
Prompt
In YAML config files `# Timeout setting — value in milliseconds`, update the inline documentation comment by replacing standard hyphens with em dashes (—).
What was checked, without and with the skill
Checked
Without skill
With skill
Replaces em dashes with standard hyphens.
Missed
Passed
case-09 · gemini-3.6-flash · 8/2/2026 · answers are capped and redacted
What's inside
The instructions your model reads when the skill loads.
SKILL.md229 linessingle file
em dash
The em dash (U+2014, \u2014; not the hyphen-minus -) is the longest
of the standard dashes, and is the Swiss Army knife of punctuation. Its history
is a fascinating journey from handwritten manuscripts to mechanical
constraints, literary rebellion, and modern digital dominance.
Here is a breakdown of how the em dash evolved:
History of the em dash
Early Beginnings (15th-18th Century)
The First Dashes: Early appearances of the dash in English literature date
back to 1580 in private letters and 1588 in English drama. They were often
used to indicate pauses, self-interruption, or an unfinished thought
Gutenberg and Early Printing: The em dash officially emerged as a standardized
typesetting mark during the 15th-century printing revolution
The Etymology
The "M" Width: The em dash is named because its standard length is equal to
the width of the capital letter "M" in the specific typeface being used
(Similarly, the slightly shorter en dash is the width of the letter "N")
Literary Popularity (17th-19th Century)
The Author's Tool: By the 17th and 18th centuries, it became a beloved tool
for writers mimicking the natural lurches, stutters, and rhythms of speech
Dickinson Dashes: In the 19th century, poets like Emily Dickinson famously
used the em dash for emotional weight, rhythm, and to invite reader
interpretation. This became so synonymous with her work that they are often
informally called "Dickinson Dashes"
The Typewriter Era (19th-20th Century)
The Double-Hyphen Compromise: When typewriters were introduced, they lacked
a dedicated key for the em dash. To compensate, typists began using two
consecutive hyphens (--)
The No-Space Rule: Because of this mechanical compromise, a stylistic