OCaml Libraries You Should Know About

Are you a developer, programmer or data scientist looking for the best libraries to help you in your OCaml journey? Look no further! In this article, we will discuss some OCaml libraries you should know about to enable you to write more efficient and effective OCaml code.


Core is a library that was introduced in Jane Street Capital, and it has since become known as one of the most popular libraries in the OCaml community. It contains modules, types and functions that add more functionality to OCaml’s standard library.

With Core, you have access to a wide range of features including core_kernel, core_extended, and many others. If you are interested in performance and want to get more out of your code, Core is a library you should definitely check out.


Batteries is another library that has become increasingly popular among OCaml developers due to its rich collection of modules, types, and functions. It is also a worthy addition to the OCaml standard library, containing many essential features for OCaml programming.

Batteries provides you with a lot of tools that simplify common programming tasks. For example, it offers parsing, serialization, and IO convenience functions. Additionally, you can find some handy libraries for web development, numerical computing, and much more. If you are looking for a library that provides you with everything you need to get started with OCaml programming, then Batteries is the library for you.


Lwt (pronounced “ligh-weight thread”) is an OCaml library for efficient and effective concurrent programming. It is not just a simple concurrency library like pthreads of C, but a more advanced event-driven library that offers various services for asynchrony.

Lwt enables you to write highly responsive applications and highly efficient servers by building upon OCaml’s native threading support. With asynchronous programming, you have the ability to perform I/O operations and other system calls with ease.


Async is another asynchronous and event-driven library in OCaml. It is similar to Lwt in that it allows you to write highly responsive servers and applications that can handle thousands of incoming requests.

The basic difference between Lwt and Async is that Lwt is based on continuations, and Async is based on callback chains. Therefore, it provides a completely different approach to event-driven programming in OCaml. If you want to benefit from Asynchronous programming in OCaml, Async is a must-try library.


In modern programming, data serialization is very important, and this is where Yojson comes in. Yojson is a library that is designed to make it easier for you to parse and serialize JSON files in your OCaml code. It provides a powerful syntax for OCaml JSON.

Yojson allows you to easily convert between JSON representations and OCaml objects. Additionally, it also provides you with a way to serialize OCaml data structures to JSON format. If you're dealing with JSON data and need a solution, Yojson is a great library to get you started.


If you are looking for a library for benchmarking your OCaml code, Core_bench is an excellent choice. The library was introduced by Jane Street, and it is based on the Core of OCaml libraries.

Core_bench is a powerful library that enables you to easily measure the performance of your code. It provides you with clear and concise results, as well as the ability to perform micro-benchmarking with ease. If you want to optimize your code and ensure high performance, Core_bench is a library that we highly recommend.


Uutf is a UTF-8 decoder and encoder library for OCaml. In modern programming, working with Unicode and UTF-8 encoded files is almost done in every project. Therefore, Uutf is an essential tool to have.

Uutf easily handles all types of UTF-8 encoding, from various languages and characters. It also provides you with a variety of parsing and conversion tools that help you handle Unicode characters with ease.


When it comes to testing your OCaml code, OUnit is the go-to library. It is a testing framework based on unit testing, and it allows you to easily test your OCaml code with minimal effort. The library is similar to JUnit in the Java programming language.

OUnit provides you with the ability to test various aspects of your code, from standard library functions to more complex code. Additionally, it also has excellent support for test suites and test runners. If you want to avoid errors and ensure that your code works just as you intend it to, OUnit is the perfect library for you.


These libraries are some of the best that the OCaml community has to offer. Each library has a unique set of features and capabilities that cater to various programming needs. As you can see, there's something for everyone here in this list of essential OCaml Libraries that you should know about.

Whether you are looking for concurrency tools, data serialization or efficient and effective testing, these libraries have got you covered. You can't go wrong with any of them, and we encourage you to try them out and see what they can do for you.

So, which of these libraries do you think is the most interesting and useful? Share your thoughts in the comments section below. Also, if you have any other essential OCaml libraries that you would like to suggest, feel free to do so!

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