Twitter’s policy changes (and rollbacks, and further changes, and rollbacks again, and finally settling on the original change) since going fully private have been contentious, to say the least. But despite grabbing worldwide headlines, few have had measurable, direct impacts on the experience of using the social network. That’s about to change in a big way: newly altered developer terms effectively make third-party Twitter apps on all platforms against the rules.

As has been the case lately, Twitter effectively made the change before telling anyone, and before actually recording it in the 5000-word developer terms and conditions. Major Twitter clients suddenly found themselves cut off from the API last week, well before the change in terms yesterday. Engadget reports that Twitter claimed it was “enforcing long-standing API rules,” which appears to be false — it simply cut access before retroactively changing the rules to cut access to apps not published by the company itself.

While other platforms and smaller tools may be able to retain access to the Twitter API, developers are now not allowed to “create or attempt to create a substitute or similar service or product to the Twitter Applications.” That makes Twitter’s official website and apps the only permitted way to access the core tweeting and browsing functions. Fenix, a popular Twitter app for Android and iOS, has not shown any new tweets since January 12th.

Twitter has existed since 2006, back when users were more likely to make a Tweet via text message than with a dedicated mobile app. But since the rise of smartphones, third-party Twitter clients have been an essential part of the platform, giving users access to powerful features on the go. Twitter’s own advanced web interface, TweetDeck, started out as a third-party desktop app. Third-party app developers, many of whom have made companies and livelihoods off of supporting the social network, have not been contacted. Twitter has had a rocky relationship with app developers in the past, but seemed to accept their necessity over the last few years.

Twitter’s strategy appears to be to drive users towards its own apps and websites, where it can tightly control the experience (and gain the most advertising revenue). As a company newly privatized by sensationalist investor Elon Musk, Twitter no longer has to announce its financial data publicly. But analysts estimate that its revenue has shrunk by up to 40 percent as advertisers leave the platform over concerns for stability and content.