Style Guide

Days, months, times, numbers

Rule	Example
Abbreviate months with 6+ letters if used with a specific date. Spell months with 5 or fewer letters. Do not use 1st, 2nd, 3rd, 4th, etc.	Jan. 1, Feb. 2, March 3, April 4, May 5, June 6, July 7, Aug. 8, Sept. 9, Oct. 10, Nov. 11, Dec. 12
Spell the month when used without a specific date.	In September, the leadership team... The session begins in February 2016.
Do not abbreviate days of the week.	Wednesday, June 1
For time, use numerals, a space, lowercase letters, and periods for a.m. and p.m. Do not use extra zeros on times. Specify time zone (include "D" if daylight savings is in effect). Include UTC time for global audiences.	7 p.m. EDT (11 p.m. UTC) 10:15 a.m. ET (3:15 p.m. UTC) 8 a.m.-2 p.m. 8-11 a.m. Bookmark this time zone converter.
Spell out numbers under 10. Use numerals for 10 and above, unless it's the first word of the sentence.	There are five directors. No, wait. There are 15. Sixteen, now that I count them.

Rule	Example
Always use the Oxford (serial) comma.	Apples, oranges, and bananas.
Avoid exclamation points.	No more than one per document. Zero, if possible.
Avoid ampersands (&) or plus signs (+).	Use only if truly necessary to omit 2 extra characters, in which case, use plus sign.
Do not hyphenate "open source"	Follow Open Source Initiative guidance

Rule	Example
Use title case capitalization for titles of guidebook chapters.
Use sentence case capitalization for headlines, headings, subheadings, job titles, and most other situations. (Capitalize only first word, proper nouns, and first word after a colon or em-dash.) Exceptions: Use title case for product, event, and award titles. See additional tips.	Join us for a town hall on Super Project 1.0 with vice president Mike Smith Favorite beverage of ALDP graduates: Milk Happening today—The OpenStack Summit Google named among Fortune's Most Innovative Companies

Rule	Example
Avoid acronyms. Spell out, unless it's something that's known primarily as an acronym.	HTML (not "HyperText Markup Language")
Use two-letter abbreviations for U.S. states. Spell out countries (except when using "U.S." as an adjective).	Austin, TX See stateabbreviations.us Brno, Czech Republic In the United States vs. in U.S. history

Essential = no comma	Nonessential = comma
I will give the document to my peer Chris. (I have more than one peer. Chris’s name is essential info and should not be set off with a comma.)	I will give the document to my director, Kim. (I have only one director. Her name is nonessential and thus set off with a comma.)
We visited Berlin too. ("Too" is an adverb. When a sentence ends with an adverb that is essential to the meaning of the sentence, the adverb should not be set off with a comma.)	Mary Smith, a staff writer at the Big City Times, recently wrote a book on that subject. (Nonessential information requires a comma.)

That	Which
John's cars that are leased are never kept clean. (The dirty cars are specifically those that John leased; John might have non-leased cars that are kept clean.)	John’s cars, which are leased, are never kept clean. (All of John’s cars are dirty. The fact that those cars are leased is not essential to the meaning of the sentence.)

Rule	Example
Use inline links when referencing something accessible primarily online, such as an article published on a news website, or a video—something the reader can choose to view immediately.	See the Contributor Covenant for additional detail. Shane Curcuru explains this concept in his 2020 presentation on The Apache Way.
If a sentence contains an inline link, do not include language that "points" readers to linked resources. Do not hyperlink referential language.	Read more on that topic here. Shaun McCance explains community documentation standards in this video.
Use footnotes when referencing something accessible primarily offline, such as an article published in a book or an episode of a television show—something the reader would need to view after reading.	This is a rather important concept[^producing-oss]. [^producing-oss]: For more on this, see Chapter 4 of Producing Open Source Software by Karl Fogel.
Use footnotes when adding notes or ancillary details as background or context for a reader.	Projects like The Open Source Way have very peculiar footnote styles[^osw-footnotes]. [^osw-foonotes]: Incidentally, the Open Source Way project refined its footnote guidelines after five years of publication.