I am have been using Byword as a simple markdown text editor and for publishing to Tumblr though I have had some issues with the app recently. Does anyone have any advice on a lightweight markdown editor to recommend? Thanks in advance.
[Edit: In relation to the above, I am on iOS 13. The issue is that the iOS version won’t seem to take my login credentials even when confirmed they are correct but I get a login error. As a replacement $, I would say sub-$80.]
First, it would help if you told use which OS you’re asking about. 
And your budget.
Regardless, if you do a search you’ll find many threads about Markdown editors for both Mac and iOS.
A great free Mac option is Typora
Thanks for the recommendation. I have updated my post to reflect your excellent questions.
You might want to look at Drafts.
I don’t know if it posts directly into tumblr, but it seems to send text to just about anything.
Thanks! I appreciate the advice.
Great, another text editor… ok ok I promise I won’t check it out 
Mweb/iOS is a free download so you can easily check it out. But I think you need the Pro unlock to use it for static website export and Tumblr. (I got MWeb for Mac for $3 as part of a 2018 BundleHunt deal [currently $19.99 in the MAS], but I never bought the $8.99 iOS unlock.)
Hehe indeed.
I’ll put it in my newly created org-mode list of text editors 
Try IA Writer. They have a free trial for the Mac. It’s $29.99 for Mac and $8.99 for iOS. You can export markdown and then share using iOS share sheet to the app you want. In this case Tumblr.
Agree with iA Writer.
iAwriter is excellent , especially fo longer form writing . Textastic is an excellent iOs editor As well.
You could try 1Writer for iOS.
This looks fantastic. Thanks!
Thanks everyone for your advice. I greatly appreciate it and you have given me some good options.
IA Writer here as well. The product is “constantly” updated with useful features.
Thanks! I appreciate the insight. iA Writer is definitely on my radar.