API-discovery-11-ways-to-find-apis-nordic-apis-01In the world of application programming interfaces or APIs, there are differing methods for cataloging these services in order to make them discoverable. Today we highlight 11 different ways to find APIs, including all the major API directories, and offer insights into the past and potential future of API discovery trends.

Defining ‘API Discovery’

Certainly major headlines can spread the news of an API release, but developers need unique integrations for their specific situation, which may not match the API release of the week. Thus, API directories and API-specific search engines have emerged as a win-win scenario — they help market APIs from the provider side, and help developers discover the perfect match for their systems.

API directories are as diverse as the space itself — each with it’s own method of collecting and cataloging APIs. But which discovery format can scale with the future growth of the API industry? What search style presents the most relevant results to efficiently help developers find the right API for their application?

Manual Vs Automation

Imagine that rather than automatically scanning the web, Google maintained a single database and hired a team to contact business owners to inquire if they had a website. That’s essentially the manual legwork that’s been done to grow API directories like ProgrammableWeb or PublicAPIs.com to date. Hand-curation is feasible in the short run, but some feel the scalability of this process is weak if we anticipate future growth in the hundreds of thousands — or millions of APIs. To this end, API search engines have been developed such as APIs.io or APIHound that leverage smart automation to increase scalability and standardize the cataloging process. But can they determine relevancy, vetting APIs as well as the human can?

11+ Ways to Find APIs

We’ll now explore fifteen approaches to finding APIs, outlining major API directories and giving a short review of their services.

1: ProgrammableWeb

Owned by Mulesoft, ProgrammableWeb distributes API-related press releases, news articles, reviews, and maintains the world’s largest hand-curated directory of APIs — now measured at nearly 14,000.


In addition to APIs, the database also catalogues mashups and developer tools like SDKs, frameworks, libraries, and code samples. A lot of work goes into searching for APIs and vetting user-submitted APIs, and unique descriptions on API functionalities accompany each profile. The directory has an intricate tagging system, enabling a user to browse hyper-specific categories relevant to their app’s industry.

They are also a consistent publishing machine, shooting out articles on new API releases, code tutorials, reviews, and more every day. Utilizing all their internal data, the PW.com research center also provides helpful resources for directing presentations on the API economy.

PW.com is exhaustive. With such a large collection, a potential problem is that there isn’t a quality ranking assigned to the APIs, and since the database is hand-curated, deprecated APIs are often left sitting in the directory. Acting solely as a directory and journal, PW.com retains a fair amount of objectivity on the API economy.

Check out additional Ways to Market Your API

2: PublicAPIs.com by Mashape

PublicAPIs.com is a directory of over 5,000 APIs, owned by Mashape, a well known API management platform and marketplace.


Visitors can search through and compare their array of API profiles, which include short descriptions and links to the provider’s documentation. You can also suggest new APIs to expand the directory. Some API providers use Mashape as their main API portal, while others use it as an extension of their API presence. With some documentation provided on the Mashape profiles, you can test calls and check endpoints.

Mashape’s API collections also lists popular APIs grouped by category. Mashape also offers GituHub integration, a helpful glossary of API lingo to help onboard people that are new to the technical terms associated wtih developing and consuming APIs.

3: APIs.io

At 7 characters, “APIs.io” certainly wins for brevity. Powered by 3Scale, API Evangelist, and API Tools, the {API}Search engine uses a kind of metadata to automate API discovery.apis.io-API-discovery-nordic-apis

”The only way to discover APIs and their properties is via human driven search through public search engines or in hand curated API Directory listings. While these methods work, neither can scale to the potentially hundreds of thousands and millions of APIs which will be published over the next few years…The objective of APIs.json is to help fix this problem by making it easy for people to signpost where the APIs on a given domain are and provide information on how they work. The format is simple and extensible and can be put into any web root domain for discovery.”

Still in an experimental phase, the APIs.json format definitions are open sourced, and ongoing discussion occurs in this Google group. Though the directory is still in it’s infancy, APIs.io or a derivative could be a scalable alternative to traditional modes of API cataloging.

4: API Hound

Relatively new to the API discovery game, API Hound uses machine scanners to find APIs. According to the API Hound blog, the service uses keyword searches to automatically scan the web for APIs. Textual analysis associates the results with specific categories, allowing APIs to be ranked in relevancy fueled by undisclosed algorithms. Search results provide direct links to the API provider’s site.

API Hound- API discovery-nordic-apis

“We launched APIHound because -like you- we depend on finding APIs to build cool stuff. We searched for a good API directory, but all we found were sites like ProgrammableWeb that have been manually collecting APIs for years and PublicAPIs which has a very small API database. There had to be more APIs out there waiting to be found.We decided it was time to bring API Searching into the 21st century. APIHound is continuously examining billions of pages to locate the best API resources.The result is that APIHound has uncovered over 50,000 APIs indexed, categorized, and available for searching.”

Though site architecture could use some work — all data is populated by the URLs, the user-facing search results are not intuitively displayed, no profiles for the APIs exist — the purported 50,000 APIs that the engine can purportedly access makes the service no laughing matter.

5: API For That

API For That is a hand-curated API directory. Organized into about 20 industry categories, API For That catalogues an estimated 400+ API profiles with links to documentation, a provider home page, and a short description for each API. The site encourages API developers to submit their APIs into the directory, and once an hour their Twitter tweets a new API that has been recently added.


”We are bringing APIs from all over the web and beyond into one location. We help you find exactly what you’re looking for by sorting them, categorizing them, and keeping them up to date.”

6: Google APIs Discovery Service

Due to the vastness of the Google APIs collection, the Google APIs Discovery Service can programmatically return data on Google APIs through a “lightweight, JSON-based API that exposes machine-readable metadata.” Other than the machine-readable format, the APIs Explorer provides an interactive web tool for human eyes.


7: Exicon

Exicon, an app management service, provides a directory of 1900 APIs sortable by industry type, including SMS APIs, bitcoin, social, and much more.


8: Mashery API Network

Mashery hosts a package of over 40 APIs from various providers. Their directory of APIs caters to categories like business services, media, eCommerce, location, health, and more. Only listing Mashery-powered APIs, it’s not an all-inclusive directory. Other than the listing, Mashery offers a suite of tools designed for developers, packed with open source interactive documentation tools.


9: Azure Marketplace by Microsoft

Microsoft Azure is amping up its developer services game. Computer vision, face APIs, speech TTS APIs, and more are all part of some developer services powered by Azure for cloud applications listed in their marketplace.

Read More: More Ways to Market Your API’s Operations Stage

10: Algorithmia

Who says the genius of academic computer scientists should stay on campus? Algorithmia provides an open marketplace for mathematicians to expose their algorithms. This enables smart micro tools in the fields of textual analysis, machine learning, computer vision, audio & video, graphs, computational mathematics and more to be exposed and integrated into apps. Though technically throttled through the Algorithmia API, the quickly expanding array of micro tools makes this an API directory in it’s own right.


Developers can expose these algorithms in a RESTful JSON format for integration into third party apps, or can upload their own to monetize the system and play the algorithm market.

11: Product Hunt

Product Hunt is a community-curated directory of technology products that mimics the Reddit up-vote style. Though not exhaustive or explicitly related to APIs, many new APIs are often submitted and disseminated throughout the community, or arranged into favorite lists. Due to the crowd-sourced and somewhat competitive nature of the platform, it doesn’t hurt to follow Product Hunt to keep on the lookout for the freshest technologies and APIs.


12: API Food

Self-touted as “the largest and fastest API directory in the universe,” API Food really IS fast. It uses the Algolia API and displays search results in real time, pulling data from Mashape’s PublicAPIs.com, ProgrammableWeb, and manually profiled APIs.

API Food directory

13: IBM’s API Harmony

IBM’s API directory takes a contextual approach to discovering APIs, structuring relationships between APIs based on their use cases and related information, such as developer discussions, usage advice, and Github projects using the API. Browse on API Harmony by search field or see their Featured, Popular, and Latest APIs lists.

IBM API Harmony directory

14: APIs.guru

APIs.guru is a machine-readable Wikipedia for publicly available REST APIs. The site accepts URLs for publicly hosted API specifications, and converts formats into the Swagger 2.0 / Open API Specification, automatically updating when specs change. You browse the growing APIs.guru collection here, and view each specification in JSON or YAML. API owners or contributors or can add an API. They also provide their own API to access the directory programmatically.

15: RapidAPI.com

RapidAPI.com is a curated marketplace of high impact APIs. The site aggregates some the “world’s top APIs” into subcategories like Payment, eCommerce, Health, Geolocation, and other specific areas. Each API profile lists specific endpoints unique to the service. RapidAPI also allows users to test APIs and embed them into their apps, all through the RapidAPI account panel, allowing developers to track and monitor their API dependencies.

A Short History of API Discovery

Things are only catalogued if there are too many of them to count. So, when we talk about discovery, we must first talk about growth. If compared to the trend in website growth in the 90s and early 2000s, a similar exponential growth has occurred with APIs. Now estimated at over 14,000 public APIs in existence, the world is quickly becoming too large to manage, too diverse to know all containments, too extraordinary to recall.

Enter API Discovery. For John Musser, ProgrammableWeb didn’t emerge because he saw a business opportunity — it was out of pure necessity. Musser began to hand-catalogue web APIs while preparing for a completely separate project, and in the process realized that no directory for APIs existed at the time. In 2005, he launched a simple site, which quickly received a lot of attention. By 2008, PW.com had 1,000 APIs listed. As a community hub, the ProgrammableWeb directory grew larger, and satisfied the needs of developers looking to create mashups, mobile apps, web apps, and more with these new, somewhat unprecedented technologies.

In 2014 we saw the emergence of a new breed of API discovery – automation. Powered by the minds behind 3Scale, API Evangelist, and APITools, APIs.io works on the proposed APIs.json discovery format, essentially a tag API providers can add to their code to automatically submit their API to the directory. What began with a few APIs has quickly emerged into nearly one thousand APIs.

Aside from the APIs.json discovery format, as we’ve covered above, today there are a slew of API management providers, API directories, listings, marketplaces, search engines, and so forth, each with their own method of making sense of the API jungle. Still, even with these tools, it’s important to note that API discovery may depend on word of mouth and luck. This takes the form of talk at developer conferences, meetups, hackathons, sound bites on TechCrunch, a 10 minute fame on Product Hunt, or perhaps an integration walkthrough on the Nordic APIs blog.

The Future of API Discovery

As APIs become more and more ubiquitous, the way they are catalogued and found naturally becomes an increasing concern. Treating an API as a product, providers must consider all possible marketing attempts — and in this space, searchability is key. This may mean adding your API to all the applicable directories mentioned above to maximize exposure.

Though API directories like PublicAPIs have a nice user interface with curated collections, they require manual updating. The prospect of machine-machine automation offers benefits like auto-update of API information and the ability to crawl, offering up some tasty benefits to the future of API discovery.

Have any thoughts on what should be done to help APIs become more discoverable? Did we leave out an API directory or API discovery service? Please share below!

Bill Doerrfeld

About Bill Doerrfeld

Bill Conrad Doerrfeld is an API specialist, focusing on API economy research and marketing strategy for developer programs. He is the Editor in Chief for Nordic APIs, and formerly Directory Manager & Associate Editor at ProgrammableWeb. Follow him on Twitter, visit his personal website, or reach out via email.


    Hey Bill,

    Nice Article! Web Service Discovery has been an active area of research in Academia, but things were different because of UDDI and single format (WSDL). Web API discovery is way more challenging.

    By the way, did you get a chance to look at sdks.io?

    It has a crawler lets you discover APIs from 8 public repositories. It has near 11,000 APIs from Github alone.

    – Adeel

  • Bill C. Doerrfeld

    updated this article and added API Harmony! thanks.