12 Popular Open Source APIs

Open Source software is defined as software in which Source Code is open for programmers to modify, share, and create applications without paying licensing fees. Developers tend to love Open Source software, mainly because it drives innovation and creativity. Luckily for them, ProgrammableWeb lists hundreds of Application Programming Interfaces, or APIs, in its Open Source category.

The category covers a huge variety of open projects that developers can integrate with to create applications. These categories include Government, Business, Artificial Intelligence, Speech, Recognition, Automobile, Music and Arts, IoT, Food and Entertainment databases, DevOps, Application Development, Healthcare & Fitness, and even Finance & Banking.

Please note: It's important to distinguish the difference between an Open API (or Public API), to an Open Source API. An Open API allows a company to publicly expose data and functions for developers to create third-party applications. The antithesis to an Open API would be a Private API, which is used to facilitate integrations within internal systems. An Open Source API, on the other hand, is simply an Integration tool that connects developers to an Open Source product or service. (Read more about public vs. private APIs in our series about Maximizing the ROI on Your API. )

Whichever Open Source API a developer may be on the hunt for can probably be found in the ProgrammableWeb Open Source category. In this article, we list the twelve most popular APIs in our directory for integrating with Open Source products and services, based on website page visits.


ONLYOFFICE is an open-source Platform for business collaboration and project management. The platform includes software for managing projects, collaborating with team members, document management and a CRM. The ONLYOFFICE APITrack this API exposes the functionality of the platform and gives developers programmatic access to it. Users can perform standard CRUD operations on groups, files, projects, forums, people and more.

2. TensorFlow API

TensorFlow is a scalable open-source Machine Learning Library for research and production. The TensorFlow APITrack this API enables computation for using data flow graphs for scalable machine learning. It also provides developers with functions for constructing and executing a TensorFlow graph in several languages. TensorFlow 2.0 Beta was recently released with updates like eager execution, intuitive higher-level APIs, and flexible model building on any platform.

3. GitLab API

GitLab is an open-source platform for developers collaborating on code and coding projects. The GitLab REST APITrack this API allows developers to retrieve and manage users, POST and GET issues, and manage project information. A GitLab GraphQL API is also now available.

4. Odoo API

The Odoo platform has over 3,000 free open source business apps that companies can use for building a web presence, integrating sales & CRM systems, accounting and internal business management, marketing, recruiting employees, for productivity, and much more. The Odoo APITrack this API enables development for third-party applications using JSON- RPC or XML-RPC protocols using the OpenERP Framework. These traits make Odoo a good companion for eCommerce and SaaS providers.

5. Moodle API

Moodle is an open-source learning management system (LMS) designed to teach with social constructionist theories. Educators and students can benefit from this modular PHP system that aims to personalize learning environments. The Moodle Core APITrack this API offers functions for Access, Data Manipulation, and Navigation, as well as Calendar, Enrollment, Media, and many others.

6. Animal Shelter Manager API

The Animal Shelter Manager is an open-source software product for managing an animal shelter. The Animal Shelter Manager APITrack this API integrates data about animals, shelter, adoption, and care. It is targeted at animal shelters, rescue groups, and animal control facilities. The API can return animal images, thumbnails, and animal adoptable views.

7. Open AQ API

OpenAQ uses a combination of open data and open source tools as well as a global, grassroots community to fight air inequality in different locations across the world. Use the Open AQ APITrack this API to build apps that power a variety of air quality measurement tools. The API convey responses in JSON format.


8. SonarQube Web API

SonarQube provides developers with services for continuous inspection of code quality. This open-source platform can perform automatic reviews with static analysis of code to detect bugs, code smells and security vulnerabilities on 20+ programming languages including Java, C#, JavaScript, C/C++, COBOL and more. The SonarQube Web APITrack this API provides access to SonarQube functionalities from applications. A SonarQube Webhooks API is also available.

9. TheMealDB API

TheMealDB is a database of recipes with photos. TheMealDB APITrack this API enables access to an open online database of food meal recipes that integrates into applications, web, etc. This is a simple JSON API with features like high-quality transparent PNG ingredients, meal image uploads, browse meals in sequence and more. TheMealDB originated on the Kodi (open-source media app) forums as a cool way to browse recipes on users' TVs.

10. IEX Cloud

IEX Cloud is a data platform for financial applications. The IEX Cloud APITrack this API returns financial data in JSON format. With the API, developers can integrate data about historical prices, income statements, insider transactions, IPO calendar, key stats, CEO information, cryptocurrency data, social sentiment, foreign exchange, US market volume, and many other categories.

11. Jenkins Remote Access API

The Jenkins Remote Access APITrack this API provides programmatic access to Jenkins, an open-source automation server designed to support the deployment and automation of any kind of project. This API can be used to create or copy jobs, trigger a new build, or retrieve information from Jenkins for programmatic consumption.

12. Pexels API

Pexels is a stock photo service. The Pexels APITrack this API enables users to integrate photo and video search into applications. It allows users to upload and modify photos, and do machine learning-driven searches on over half of a million photos.

Pexels API
Screenshot: Pexels

The APIs listed above are just a small sampling of what can be found in the Open Source category in ProgrammableWeb's API directory. Check out more than 160 APIs170 SDKs, and 80 Source Code Samples for open source application development.

Be sure to read the next Open Source article: Kong Announces Open Source Service Mesh Control Plane: Kuma