In your blog settings you have the ability to initiate a blog export, and this will generate a backup for your blog.
Fair warning though, if you've been on the platform for a long time this archive is likely to be quite hefty in file size. This blog I have had for 5 years with 22k posts, and the export from tumblr came to be 48GB. My previous blog I made in 2011 and has 95k posts, so needless to say I did not use tumblr's built in export to back that one up.
If you want more control over exactly what you back up from your blog, I recommend that you use tumblr-utils instead. It allows you to backup specific tags, post types, and to ignore posts that you did not create (reblogs where you've added a comment count as a post you created, to be clear).
download and install python 2.7
create an application on tumblr to get an api key
extract the tumblr-utils zip and open the tumblr_backup.py file in notepad
search for "API" and paste in your OAuth consumer key
then go back to the folder where you extracted tumblr-utils and choose open folder in terminal / command prompt, or type cmd.exe in the address bar while inside the folder
now in the window that opens it should show the current path, and you can type "py -2 .\tumblr_backup.py [your options] [your blog name]" and hit enter. Example:
Backing up just my original posts from this blog with this command came to 632MB rather than 48GB, and also gave me the option to save my posts in JSON format which will be useful for converting my posts to a new format for self hosting.
On that note I'm currently looking into figuring out a simple (and ideally free) way of self hosting a static site blog that utilises activitypub, and also converting my old posts to re-host on said blog.
This post series by maho.dev on implementing activitypub with any static site is my primary source of guidance atm if you also want to try figure that out yourself, as well as having an explanation for why you'd even want to do this if you don't already know
but if tumblr goes down before I get things sorted and write up a post about it then i'll be reporting back on it via my bsky, mastodon, and toyhouse accounts
if you dont have an account on any of these I'll also be sharing an update via my personal site's RSS feed, link of which includes an explanation of what RSS is and some feed readers you can use, I highly recommend checking it out as getting a feed reader is going to be the best way you can stay connected with people if they scatter across the internet!
tldr: download tumblr-utils to backup your blog more efficiently, introduce yourself to RSS and get a feed reader to stay connected with people, consider saving mine so you can find out how to self host your blog later if tumblr goes down
