Answer: Neither — they are really only useful as a whole. A client without a server is usually little more than an non-functional wire frame and a server without a client is simply unrealized potential. Bring them together though and you have something of lasting value. So, neither matters more and each actually matters a lot less than half.
In the API world, this is an easy point to miss. The server side always wields disproportionate power by virtue of controlling the API to its services and this can easily foster an arrogance about the server’s place in the world. This effect is nicely illustrated by Twitter’s recent missteps around developer management.
The problems for Twitter all began with a blog entry. Blogs are the mouthpiece of the platform. Tucked away within an interesting entry about Twitter Cards and the potential to run applications within tweets (something that is genuinely exciting), can be found a restatement of an early warning to developers:
“(D)evelopers should not ‘build client apps that mimic or reproduce the mainstream Twitter consumer client experience.’”
Ominous stuff indeed. This was quickly picked up on by Nick Bilton writing in the New York Times Bits blog, who pointed out that the real problem is that Twitter just isn’t very good at writing client-side apps that leverage its own API. Stifling competition by leveraging the API power card can only alienate developers — and by extension the public, who are left with a single vendor solution. Suddenly, it feels like the 1980s all over again.
This ignited a firestorm of concern that was well summarized by Adam Green on ProgrammableWeb. Green acknowledged that API change is inevitable but pointed out that this is something that can be managed effectively — which is not what Twitter is doing right now.
The irony of the whole thing is that, in the past, by exercising its power position, Twitter has actually made great contributions to the API community. In mid 2010, Twitter cut off basic authentication to APIs in favor of OAuth, a drop-dead event that became known as the OAuthcalypse. Hyperbole aside, in terms of actual impact on the populace, this cut over made even Y2K look like the end of days. Given a tractable challenge, developers cope, which is really Green’s point.
What is important to realize is that API Management isn’t technical but social. Win the community over and they will move mountains. Piss them off and they will leave in droves for the next paying gig.
The thing I always remind people is that as a trend, APIs are not about technology; they are a strategy. Truth is, the technology is pretty easy — and that’s the real secret to API’s success. You see, the communications are never the thing; the app is the thing (and that is what WS-* missed). Maintaining simplicity and a low barrier to entry counts for everything because it means you can get on with building real apps.
Now, I can give you the very best infrastructure and tools to facilitate API community. But how you manage this community… Well, that is where the real work begins and — in the end — it’s all a lot less deterministic than we technologists like to admit. People are hard to manage but communities are even harder.
If there is a lesson here, it is that APIs are really about potential and that potential can only be realized when you have two sides — client and server — fully engaged. Mess this one up and you’re left with just a bunch of unused interfaces.