Enlarge / Here's the line that Twitter added to its API Developer Agreement on Jan. 19, two days after it cited "long-standing API rules" for why third-party apps may not be working. (credit: diffchecker)

"Long-standing" can apparently mean "later this week" at Elon Musk's Twitter, as the company has changed its developer agreement to seemingly justify its banning of third-party clients. The change happened two days after a vague tweet about "enforcing long-standing API rules" without pointing to any.

As noted by Internet sage Andy Baio, a text comparison (diff check) of Twitter's developer agreement between the effective dates of October 10, 2022, and January 19, 2023, shows only one change besides the effective date: a new line added to the section "Restrictions on Use of Licensed Materials." The addition restricts the ability of developers to:

c) use or access the Licensed Materials to create or attempt to create a substitute or similar service or product to the Twitter Applications;

With that, Twitter put an end to an era, one in which third-party clients not only coexisted with Twitter's official app—originally based on Tweetie, an early third-party app itself—but often introduced and drove new features. Twitter's official apps and its website are now the only reliable ways to access the service.

Enlarge / Twitter is blocking many third-party clients' access to its API while continuing to provide no explanation. (credit: Ryan J Lane/Getty Images)

Twitter has not yet explained why third-party clients like Twitterific and Tweetbot stopped working late last week. But a new report and testing by one app developer suggest the outages and lack of communication are intentional.

Internal Twitter Slack chat messages viewed by The Information (subscription required) show a senior software engineer writing in a "command center" channel that "third-party app suspensions are intentional." Another employee, asking about talking points to use when addressing the outages with product partners, was told by a product marketing manager that Twitter had "started to work on comms," but there was no delivery date, according to The Information's report.

Some Tweetbot users seemed to briefly regain account access early Sunday, without the ability to post, only to lose access again later. That resulted from Tweetbot co-creator Paul Haddad swapping out the app's API keys, but all of his keys were later revoked. That result "proves that this was intentional and we and others were specifically targeted," Haddad wrote on Mastodon Sunday evening, as noticed by The Verge.