Source: https://developers.google.com/style/commas-serial\n\n# Commas
Stay organized with collections
Save and categorize content based on your preferences.\n\n- Home\n- Products\n- Style\n\n\n## Page Summary\n\n- Use the serial (or Oxford) comma in a list of three or more items to avoid ambiguity.\n- Place a comma after introductory words and phrases, and between independent clauses joined by a coordinating conjunction.\n- Use a comma before which in nonrestrictive clauses and after conjunctive adverbs like however or therefore.\n- Generally avoid a comma before because unless it starts a nonrestrictive clause.\n- Refer to specific sections for guidance on punctuating numbers and examples.\n\nUse the serial (or Oxford) comma in a list of three or more items to avoid ambiguity.\n\nPlace a comma after introductory words and phrases, and between independent clauses joined by a coordinating conjunction.\n\nUse a comma before which in nonrestrictive clauses and after conjunctive adverbs like however or therefore.\n\nGenerally avoid a comma before because unless it starts a nonrestrictive clause.\n\nRefer to specific sections for guidance on punctuating numbers and examples.\n\nUse commas to separate items in a series, and use commas to separate certain kinds of
clauses.
Serial commas
In a series of three or more items, use a comma before the final and or
or to avoid potentially changing the meaning of the sentence. This comma is called a serial
comma or an Oxford comma.
Recommended: Locations are divided into
zones, regions, and multi-regions.
Not recommended: Locations are divided into
zones, regions and multi-regions.
Commas after introductory words and phrases
In general, place a comma after an introductory word or phrase.
Recommended: Finally, only groups that
contain parameters appear in this list.
Recommended: Based on the requirements of
your game, you can implement this method to update game information.
Commas separating two independent clauses
When a coordinating conjunction (and, but, or,
nor, for, so, or yet) separates two independent
clauses, insert a comma after the first clause (before the conjunction) unless
both clauses are very short.
Recommended: The libraries make
feed creation easier, and they ensure that only valid feeds are produced.
Not recommended: The libraries make
feed creation easier and they ensure that only valid feeds are produced.
Recommended: Type your ID and click OK.
Not recommended: Type your ID, and click
OK.
Commas separating independent from dependent clauses
When an independent clause and a dependent clause are separated by a
coordinating conjunction, insert a comma only if the sentence could
be misunderstood without one.
Recommended: Direct-access flags are
plain variables and can be read directly.
Not recommended: Direct-access flags are
plain variables, and can be read directly.
Recommended: The manager acknowledged the
last team member who entered the room, and started the meeting.
Not recommended: The manager acknowledged
the last team member who entered the room and started the meeting.
Set off other kinds of clauses
It's often a good idea to set off certain kinds of clauses with a comma or
other punctuation for clarity.
A couple of specific places where commas are a good idea:
In general, put a comma before the word which at the start of a
nonrestrictive clause. For more information about this topic, see this guide's section on relative pronouns and Grammar
Girl's page on
which versus that.
In general, put a semicolon or a period or a dash before a conjunctive
adverb, such as otherwise, however, or therefore, and put a comma after
the conjunctive adverb.
In general, don't use a comma before the causal conjunction because unless it starts a nonrestrictive clause. For more information,
see the Chicago Manual of Style Q&A entry on
using
commas with because.
Recommended
Not recommended
Name of the group, which has a maximum length of 200 characters.
Name of the group which has a maximum length of 200 characters.
The variable must have a value; otherwise, the server returns an error.
The variable must have a value otherwise the server returns an error.
You can use the same key name in multiple backend services and backend buckets, because
each set of keys is independent of the others.
You can use the same key name in multiple backend services and backend buckets because
each set of keys is independent of the others.
Punctuate numbers
For information about punctuating numbers, see Commas and decimal
points in numbers.
Punctuate examples
For information about punctuating examples, see Format examples.\n\n\n## Serial commas\n\nIn a series of three or more items, use a comma before the final and or
or to avoid potentially changing the meaning of the sentence. This comma is called a serial
comma or an Oxford comma.\n\nRecommended: Locations are divided into
zones, regions, and multi-regions.\n\nNot recommended: Locations are divided into
zones, regions and multi-regions.\n\n\n## Commas after introductory words and phrases\n\nIn general, place a comma after an introductory word or phrase.\n\nRecommended: Finally, only groups that
contain parameters appear in this list.\n\nRecommended: Based on the requirements of
your game, you can implement this method to update game information.\n\n\n## Commas separating two independent clauses\n\nWhen a coordinating conjunction (and, but, or,
nor, for, so, or yet) separates two independent
clauses, insert a comma after the first clause (before the conjunction) unless
both clauses are very short.\n\nRecommended: The libraries make
feed creation easier, and they ensure that only valid feeds are produced.\n\nNot recommended: The libraries make
feed creation easier and they ensure that only valid feeds are produced.\n\nRecommended: Type your ID and click OK.\n\nNot recommended: Type your ID, and click
OK.\n\n\n## Commas separating independent from dependent clauses\n\nWhen an independent clause and a dependent clause are separated by a
coordinating conjunction, insert a comma only if the sentence could
be misunderstood without one.\n\nRecommended: Direct-access flags are
plain variables and can be read directly.\n\nNot recommended: Direct-access flags are
plain variables, and can be read directly.\n\nRecommended: The manager acknowledged the
last team member who entered the room, and started the meeting.\n\nNot recommended: The manager acknowledged
the last team member who entered the room and started the meeting.\n\n\n## Set off other kinds of clauses\n\nIt's often a good idea to set off certain kinds of clauses with a comma or
other punctuation for clarity.\n\nA couple of specific places where commas are a good idea:\n\n- In general, put a comma before the word which at the start of a
nonrestrictive clause. For more information about this topic, see this guide's section on relative pronouns and Grammar
Girl's page on
which versus that.\n- In general, put a semicolon or a period or a dash before a conjunctive
adverb, such as otherwise, however, or therefore, and put a comma after
the conjunctive adverb.\n\nIn general, don't use a comma before the causal conjunction because unless it starts a nonrestrictive clause. For more information,
see the Chicago Manual of Style Q&A entry on
using
commas with because.\n\n\nRecommended | Not recommended\nName of the group, which has a maximum length of 200 characters. | Name of the group which has a maximum length of 200 characters.\nThe variable must have a value; otherwise, the server returns an error. | The variable must have a value otherwise the server returns an error.\nYou can use the same key name in multiple backend services and backend buckets, because
each set of keys is independent of the others. | You can use the same key name in multiple backend services and backend buckets because
each set of keys is independent of the others.\n\n\n## Punctuate numbers\n\nFor information about punctuating numbers, see Commas and decimal
points in numbers.\n\n\n## Punctuate examples\n\nFor information about punctuating examples, see Format examples.\n