8 OCaml Libraries to Make Your Life Easier

by Christine Rose on Oct 12th, 2022

OCaml is a statically-typed programming language that emphasizes readability, programmer efficiency, and semantic clarity. This powerful and efficient language has been gaining popularity among developers. The growing adoption of OCaml is because it's fast, type safe, and secure. It can be used in industries where performance and security matter, like IoT, Data Analytics, or financial services.

Like any other programming language, there are numerous libraries available for OCaml that can make your life easier as a developer. In this article, we will explore some of the top OCaml libraries that will help streamline your workflow and boost your productivity as a programmer.

All these libraries and tools are open source, so they’re distributed under a free software licence.

A Few Helpful OCaml Libraries


Lwt is a library for writing asynchronous code. It provides many helpful abstractions for writing asynchronous code such as promises and futures. This is a very useful library for writing network applications, like web servers. That said, the Eio library in the forthcoming release of OCaml 5.0 might become preferable!


Dream is described as a "tidy, feature-complete Web framework" on OCaml.org. Dream has a simple programming model where web apps are merely functions, and it supports TLS, WebSockets, and GraphQL. Plus it has cryptography helpers! It's easy-to-use and documented all in one place. The entire Dream API is available there, where you can also find many examples.


This library is used by several packages to build command line tools, which is beneficial when you want to write an executable in OCaml. Cmdliner gives programmers a simple, compositional method for turning command line arguments into OCaml values. Not only can you then pass those values to functions, Cmdliner can automatically handle syntax errors, help messages, and UNIX man page generation as well.


This colorful framework performs simple unit tests on a simple interface. Alcotest only displays faulty runs at the end of the output, along with full logs for your inspection. The straightfoward, expressive query language makes it easy to select which tests to run, and the results are displayed in a fun rainbow of colors.


Although the standard library is somehow minimalist, multiple extensions exist to make programmers' lives easier. For instance base, created and maintained by Jane Street, is used to develop critical applications by industrial users. baseis written in pure OCaml and has no dependencies other than the OCaml standard library. The base library is useful for building many applications. Read more about base in the book *Real World OCaml.


Yojson is an OCaml library for creating and reading JSON data in OCaml. JSON is a data format that is commonly used in web applications. The Yojson bindings can be used to easily generate and parse JSON data in OCaml.


This interesting OCaml library enables the user to write declarative terminal UI. Notty is based on a notion of composable images, and it delivers a more simple and expressive model than the basic terminal programming. Engineers know that programming terminals are tedious, so Notty makes it enjoyable!


PreProcessor eXtensions, or PPX for short, are used for meta-programming, like for generating boilerplate or for extending the OCaml syntax. PPX act on the AST and are integrated into the language via two AST features: attributes and extension nodes. ppxlib is a set of tools and libraries that enables programmers both to write and use PPX. See this Tarides blog post on how to write PPX and this official guide on how to use PPX.


The tools available in OCaml make it easy to prototype new applications and build production-quality software. In fact, the full release of OCaml 5.0 with Multicore support is on the horizon, and the alpha version has already been released.

OCaml libraries help you write beautiful, elegant code in this powerful and versatle language. There has never been a better time to give OCaml a try, and now you know there are beneficial libraries to help you code. The libraries covered in this article are just a few examples. For more information, please visit ocaml.org