A registry for APIs?

I recently wrote a post on LinkedIn sharing that OpenAPI could follow what MCP is doing to solve discovery. MCP introduced the registry on September 8, 2025. Their goal is to centrally “provide MCP clients with a list of MCP servers, like an app store for MCP servers.” It sounds like a fantastic approach and something I think we can replicate for APIs.

The reactions to my LinkedIn post were not at all encouraging. Reading those comments makes you feel like many people don’t want APIs to be easily discoverable. It’s interesting to see the pushback by some API industry veterans and also the arguments being used.

One comment mentions that “the business alignment is the problem.” It also mentions the failures of some API directories like ProgrammableWeb, Mashape, RapidAPI, and Postman Network. First of all, there’s a distinction to be made between API directories (or registries) and API marketplaces. ProgrammableWeb and Postman Network can be considered API directories. On the other hand, Mashape and RapidAPI are API marketplaces. The difference is that marketplaces manage the interaction of consumers with the listed APIs.

So, what happened to ProgrammableWeb to fail? It started in 2005 as an API-focused blog and a directory of APIs. ProgrammableWeb changed ownership a few times. It was sold to Alcatel-Lucent in 2010. ProgrammableWeb founder moved to Alcatel-Lucent and kept running the blog and API directory as an independent organization. Alcatel-Lucent mentioned that the reason behind the acquisition was to help foster an ecosystem of service providers. At the time Laura Merling, VP at Alcatel-Lucent said that “If you look at any organization that launches an API, you quickly realize that the one thing the most successful APIs have in common is a vibrant developer ecosystem.” Then, in 2013, ProgrammableWeb was sold to MuleSoft. MuleSoft had recently launched APIhub, an API publishing platform, and wanted to join forces with the growing API directory that ProgrammableWeb provided. Then, in 2018, MuleSoft was sold to Salesforce for $6.5 billion. ProgrammableWeb kept running until 2022, when it stopped making sense to keep a large manually curated API directory. Did ProgrammableWeb fail? I don’t think so. It lasted 17 years, from 2005 to 2022. It kept growing and growing, reaching 1,000 APIs in July 2008, and more than 25,000 APIs by the time it shut down. It was clear that the system had to change from being manually curated to something else.

What about Postman Network? Did it also fail? Let’s find out. It was launched in 2017 as a curated public directory of APIs and Postman collections. I started with a few hundred APIs, curated by Postman and its partners. In 2018, Postman introduced its private API network as a way to give companies a private way to publish and discover their APIs. This feature was well received and helped grow the public API network as companies themselves began contributing. In 2021, Postman added more community-focused features to the public API network, making it grow in the number of APIs. In 2022, it had thousands of APIs, in 2023 it reached 75,000 APIs, and in 2025 it reached more than 100,000 APIs. It looks like the growth lever was opening it to contributions from the API owners themselves instead of keeping it closely curated. Postman Network is active and growing at the time of this writing. It doesn’t look like a failure to me.

What about Mashape? Mashape wasn’t an API directory, so I’m not going to do a full analysis. Mashape started in 2009 with the goal of becoming an API marketplace. At its peak, in 2015, it listed over 15,000 APIs. It was also in that year that Mashape open-sourced the API gateway it used to manage the billions of monthly API requests, serving over 150,000 developers worldwide. Kong, its API gateway, became its main focus in 2017. Mashape sold its API marketplace business to RapidAPI and rebranded to Kong, focusing on the API gateway and management solutions. Was it a failure? I don’t think so.

And what about RapidAPI? It’s also a marketplace, not a directory. After it acquired Mashape’s API marketplace in 2017, it became the largest inventory of ready-to-use APIs with over 7,500 APIs. It served over 370,000 developers, making over 300 billion requests per month. At its peak, in 2023, RapidAPI, then rebranded to Rapid, hosted over 40,000 APIs. After having company management issues, it was sold to Nokia in 2024. It could have grown much more, I’d say. The company management lost focus and spent too many resources going after markets that didn’t scale. In that sense, we can say that it failed.

After doing this analysis, it looks like the approach that scales is the one followed by Postman. Letting API producers themselves publish their APIs is key.