Action for Drafts App, https://getdrafts.com , to update the applied tags to match a line of hashtags on the last line of the draft. Also in the Drafts Directory here https://actions.getdrafts.com/a/10l

Drafts-Sync-Tags.js

let lastLine = draft.lines[draft.lines.length- 1];

if(lastLine.startsWith('#')) {

	let re = /#([\w]+)/g;
	
	let hashtags = [...lastLine.matchAll(re)];
	let newtags = [] 
	
	// because matchAll is returning both the full hashtag and the text just get the text
	hashtags.forEach(hashtag => {
		newtags.push(hashtag[1]);
	});

	// add any tags that don't yet exist
	newtags.forEach(tag => {
		if(!draft.hasTag(tag)) {
			draft.addTag(tag);	
		} 
	});
	
	// remove any tags that aren't in the list
	draft.tags.forEach(tag => {
		if(!newtags.includes(tag)) {
			draft.removeTag(tag);
		}
	});
	
	draft.update();
}