I'm wondering what the rule is for when you post comments online. Here are some examples:
Yeah, I totally agree
I wouldn't do that myself
Would I end these with a period? Or is it acceptable to post them without one.
This is a very hard question to answer. It's the word "acceptable" that makes it so.
Is it more acceptable to use a period or more acceptable to follow the style of the particular group you're interacting with. If that same online community used question marks where most people would use commas (for some unknown reason), would you do that? If you don't you might be seen as an outsider.
My preference would be to use a period. Other people in the group you're interacting with may find the period overly pedantic. If you're worried about what is proper English grammar, then use a period. If you're worried about belonging to the group, then belong and don't.
Usually ending with period is nice. But in online space if you have just one line and you post it without period, the period is implied. However if you've multiple lines, you must use the period to differentiate between lines.
The Daily Mail recently published an article entitled Want your texts to appear sincere? DON’T use punctuation: Researchers say full stops make messages appear less trustworthy
The Washington Post also picked up on the study.
Personally I find the results disappointing but, for the record, the gist is quoting DM:
Based on the responses, text messages that ended with a full stop were rated less sincere than text messages that did not end with a period.
The students who read the notes on the paper reported that full stop or not, they felt the message was sincere.
These results suggest that punctuation can misconstrue or influence the meaning of text messages.
I wonder if same rationale could extend to the brief on-line comments mentioned in this question.