Changing a universal constant: How 280-character tweets break an API

Recently Twitter announced that they’re rolling out support for 280-character tweets; up from the 140-character limit that’s been in place since the company was founded. The controversy around whether that was a good decision continues to rage on.

More interesting than the debate is how Twitter treated adding the new longer tweets to their API. Returning new longer tweet content in a field that’s been expected since the beginning of time to always hold 140 characters would be tumultuous to say the least – for thousands of existing applications it would be as if the universal constant of gravity, something they’ve always taken for granted to be a constant, suddenly shifted from 9.81 m/s2 to 15 m/s2.

To avoid breaking those applications Twitter has treated moving to 280 characters as a backwards-incompatible API change. Tweets come back from the API containing a set of fields including text, which is each tweet’s 140-character content:

GET /1.1/statuses/user_timeline.json?screen_name=brandur

    {"id":123, "text":"tweet123 content", ...},
    {"id":124, "text":"tweet124 content", ...},
    {"id":125, "text":"tweet125 content", ...},

Even today for tweets that contain up to 280 characters, text comes back with no more than 140 characters; content that runs over is truncated with an ellipsis (…).

The rest of each tweet is still accessible, but clients must ask for it explicitly by specifying tweet_mode=extended. When they do, text is replaced by full_text, which can hold up to 280 characters.

GET /1.1/statuses/user_timeline.json?screen_name=brandur&tweet_mode=extended

    {"id":123, "full_text":"tweet123 *extended* content", ...},
    {"id":124, "full_text":"tweet124 *extended* content", ...},
    {"id":125, "full_text":"tweet125 *extended* content", ...},

The API change ensures that only clients who have vetted themselves get the upgrade, and by extension guarantees a smooth transition. There is a downside though: especially for new users, Twitter’s API is forever more complex to understand. If you’re writing a program from scratch and have never made the 140-character assumption, having to specify a special parameter to get a normal-length tweet back isn’t going to make a lot of sense.

This is where API versioning comes in. Twitter’s technically using path-based versioning, and could increment the /1.1 that prefixes every URL to a /1.2. They haven’t though, and I suspect that they won’t for some time. The trouble with such an explicit versioning scheme is that it introduces two divergent schemes that will both need to be maintained in near perpetuity (you’re not going to have everyone moving off of 1.1 anytime soon).

This is a near-perfect case study in compatibility because a change in content length seems totally benign on the surface, but the effort involved shows just how far careful platforms are willing to go not to break their users.

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