Tumblr is a social networking microblog.
Users can change their account names into the format used for deleted accounts. Specifically, USERNAME-deactivated-[Any amount of digits, 0-9]. Users who do this are inaccessible via their main account page, or directly linked to posts. Their posts will still show up in searches, and their "archive" URL will work. This doesn't seem to have an effect on the API, and tumblr-utils will still work just fine. For an example of this tomfoolery, see the archive page of user "diediedie3344-deactivated-204913".
Another quirk is that Tumblr accounts that appear to be on a different domain name are still accessible at, and show up in searches as, their account name. Trying to go to any page on the accountname.tumblr.com end redirects you to the same page on the custom-url-here.com page. For an example of this behavior, see user "homosethsual" which redirects to ranpos.star.is
In December 2015, Yahoo put their Tumblr service into the "decide on" category in their Action Plan, according to their 2015 shareholder presentation.
In June 2017, Tumblr tightened up "Safe mode", which limits "sensitive content" to all users below 18 years old and the viewing of blogs marked as explicit, potentially causing a major move-away from Tumblr due to Internet Backdraft from its users. Given Yahoo's tendency to ax things that become less popular than expected, it might be important to keep an eye out for it.
As of 30th of July 2017,
it is no longer possible to access NSFW accounts outside of http://tumblr.com/blog/<name> URLs. Attempting to access an NSFW account normally will now cause infinite redirecting. NSFW marked Tumblrs are inaccessible to signed out users.
Lists of Tumblr blogs
- Project Sonar 2018-10-26 FDNS data) (2.6 million;
- (~7 million, scraped in april 2018, csv formatted with additional metadata. blog,url,post count,likes count, ... 5th csv field should be the is_nsfw indicator)
- (~12 million, scraped in april 2018, contains everything from above and more. schema as stated in first line of the file: tumblelog,url,posts,likes,adult,nsfw,groupchan)
- (96.7k; scraped from Bing on 2018-12-05 with the adult keyword list at )
As the sources above are incomplete, blogs to be archived can also be submitted using this form.
Internet Archive collections
Tens of thousands subdomains from the December 2018 emergency archival are flowing to https://archive.org/details/archiveteam_tumblr
Over 800 domains were archived in 2015: WildArchives-Tumblr.
- gettumblrpics, simple script to download images from a tumblr feed as they appear in it
- tumblr-utils, tumblr_backup.py can make a local backup of posts (XML default), video, audio and images. Uses APIv2
- Tumblrsagi, Code to grab blogs from the API and stuff them into a database for rehosting, used by this tumblr archive
-  can automatically mirror the contents of a tumblr blog as they are posted, which may be useful for maintaining an offsite-copy which can be archived later.
- TumblThree, Can archive an entire blog by feeding it an URL, including asks, text posts and reblogs to XML format and can download all images. Downloadable here. Windows only until the dev implements mono support.