Awesome OCaml Awesome

Everything you'll ever need on the road to mastering OCaml.

A curated list of references to awesome OCaml tools, frameworks, libraries and articles. Additionally there is a collection of freely available books, papers and presentations.

A community-driven review of the current state of the OCaml ecosystem and its suitability for various programming domains and tasks can be found in:

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If you are beginner and want to learn the basics of OCaml programming here is the Beginner's guide to OCaml beginner's guides.



Algorithms and Data Structures

Application Libraries

  • Batteries Included309 104 – A community-maintained foundation library for your OCaml projects.
  • Cmdliner65 19 – Declarative definition of command line interfaces for OCaml.
  • Core586 74 – Jane Street Capital's full-fledged standard library overlay. A portable subset of Core is also available: Core_kernel120 43 .
  • Base132 18 - Jane Street Capital's dependency-free, quick-compiling, fully-portable across any environment that can run OCaml code standard library.
  • React – React is an OCaml module for functional reactive programming (FRP). It provides support to program with time varying values: declarative events and signals.
  • Minicli – Minimalist library for command line parsing.
  • ctypes183 53 – Library for binding to C libraries using pure OCaml.
  • easy-format16 12 – Pretty-printing library for OCaml.
  • ocaml-rpc40 19 – Light library to deal with RPCs in OCaml.
  • ocaml-containers186 44 – A lightweight, modular standard library extension, string library and interfaces to various libraries (bigarrays, unix, etc...). BSD license.



  • More OCaml: Algorithms, Methods, and Diversions – In More OCaml John Whitington takes a meandering tour of functional programming with OCaml, introducing various language features and describing some classic algorithms. The book ends with a large worked example dealing with the production of PDF files. There are questions for each chapter together with worked answers and hints.
  • How to Think Like a (Functional) Programmer by Allen Downey and Nicholas Monje – How to Think Like a Computer Scientist is an introductory programming textbook based on the OCaml language. It is a modified version of Think Python by Allen Downey. It is intended for newcomers to programming and also those who know some programming but want to learn programming in the function-oriented paradigm, or those who simply want to learn OCaml.
  • OCaml from the Very Beginning by J. Whitington - OCaml from the Very Beginning will appeal both to new programmers, and experienced programmers eager to explore functional languages such as OCaml.
  • Pearls of Functional Algorithm Design by Richard Bird - It summaries 30 hard algorithm problems in function programming world. Although it is for Haskell, the algorithm problems are very interesting and trying to solve them in OCaml also helps the thinking of functional programming. Partial solutions in OCaml are here.
  • Real World OCaml by Y. Minsky, A. Madhavapeddy and J. Hickey - Functional programming for the masses.
  • Unix System Programming in OCaml by X. Leroy and D. Rémy – Introduction to Unix system programming, with an emphasis on communications between processes.
  • Using, Understanding, and Unraveling OCaml – This book describes both the OCaml language and the theoretical grounds behind its powerful type system.
  • Purely Functional Data Structures - This is the first or only book focus on various data structures in FP world. A must-read one.
  • OCaml for Scientists - by Jon Harrod.

Code Analysis and Linters

  • Mascot - Mascot is a style-checker for OCaml sources
  • pfff2k 189 – pfff is a set of tools and APIs to perform some static analysis, dynamic analysis, code visualizations, code navigations, or style-preserving source-to-source transformations such as refactorings on source code.
  • infer8k 1k - infer is a static analyzer for Java, C and Objective-C
  • flow17k 2k - flow is a static type checker for JavaScript
  • Ocamllint57 3 - Ocamllint detects common errors in OCaml code
  • BetterErrors - BetterErrors improves error messages of the OCaml compiler (Make OCaml Errors Great Again.)
  • SLAyer - SLAyer is an automatic formal verification tool that uses separation logic to verify memory safety of C programs.
  • MemCAD8 4 - MemCAD is an abstract interpreter for shape analysis. MemCAD can verify C programs manipulating complex data structures.
  • BAP420 117 - BAP is a reverse engineering and program analysis platform that targets binary programs.

Compilers and Compiler Tools


Two concurrency libraries exist in OCaml: Lwt and Async. They provide very similar functionality but make radically different decisions with regards to error handling and internal implementation details (see the links below for more details). Real World OCaml uses Async but a version of the code examples translated to Lwt29 2 is also available.


  • Bindings
    • Dbm — A binding to the NDBM/GDBM Unix "databases".
    • – An OCaml driver for Mongodb
    • PG'OCaml — A type-safe interface to PostgreSQL in pure OCaml.
      • ppx_pgsql8 1 – A syntax extension for embedded SQL queries using PG'OCaml.
    • PostgreSQL-OCaml — An interface to PostgreSQL through the C API (libpq).
    • SQLite335 16 — OCaml bindings to the SQLite3 database.
    • Sqlite3EZ — Thin wrapper for SQLite3 with a simplified interface.
    • ocaml-redis28 16 – Redis bindings for OCaml.
    • mysql – Bindings to libmysqlclient for interacting with MySQL databases.
    • mysql_protocol2 0 – Implementation of MySQL Protocol with the Bitstring library.
  • New Implementations
    • Irmin800 74 — A distributed database that follows the same design principles as Git.
    • Obigstore — A database with BigTable-like data model atop LevelDB.
    • RunOrg6 0 - It is a WIP database server written in OCaml.
  • Overlays
    • Macaque27 10 — Macaque is a library for safe and flexible database queries using comprehensions on top of PG'OCaml.
    • ORM32 5 — ORM for SQLite.
  • Articles:


Developer Tools

  • Try OCaml – Try OCaml in your web browser.
  • codingground – Compile and execute OCaml code online.
  • iocaml148 21 – An OCaml kernel for the IPython notebook.
  • utop392 53 – Universal toplevel for OCaml with support of multiline edition, history, real-time and context sensitive completion, colors, and more.
  • ocamlbrowser – A source and compiled interface browser, written using LablTk. Included in the standard distribution for ocaml <= 4.01 and with labltk for ocaml >= 4.02.
  • ghim12 1 – A command-line tool to manage Github Issues.
  • OCaml Yeoman Generator15 1 – Yeoman generator to scaffold OCaml modules.
  • Foreign Function Interface:
  • Editor Integration:
    • merlin229 38 – Context sensitive completion for Ocaml in Vim and Emacs.
    • tuareg178 44 - OCaml mode for Emacs that can run the toplevel and the debugger within Emacs.
    • vscode-ocaml112 15 – extension that provides OCaml language support for VSCode
    • Sublime better ocaml5 0 – Better OCaml mode for Sublime Text.
    • ocp-index – Easy access to the interface information of installed OCaml libraries. Provides standalone tools like ocp-browser and ocp-grep.
    • ocp-indent – Indentation tool for OCaml, to be used from editors like Emacs and Vim.
  • Code coverage:


Formal Software Verification

  • Coq – Coq is a formal proof management system. It provides a formal language to write mathematical definitions, executable algorithms and theorems together with an environment for semi-interactive development of machine-checked proofs.
  • Why3 – Why3 is a platform for deductive program verification. It provides a rich language for specification and programming, called WhyML, and relies on external theorem provers, both automated and interactive, to discharge verification conditions.
  • Alt-Ergo – Alt-Ergo is an open-source SMT solver dedicated to the proof of mathematical formulas generated in the context of program verification.



  • 2D
    • archimedes — 2D plotting library.
    • cairo217 2 — Binding to Cairo, a 2D Vector Graphics Library. Integrates well with lablgtk.
    • Vg40 7 – Declarative 2D vector graphics for OCaml.
  • 3D
    • glMLite — OpenGL bindings for OCaml. Provides an (experimental) functional API.
    • lablgl — Interface to OpenGL. Integrates well with lablgtk.
    • tgls — Thin bindings OpenGL 3.{2,3},4.{0,1,2,3,4} and OpenGL ES {2,3}.

User Interface

  • lablgtk — GTK2 bindings for OCaml with various higher-level facilities to define GUIs.
  • lablqml7 1 – QML Qt5 bindings for OCaml.
  • labltk — Interface to the Tcl/Tk GUI framework. In the standard distribution for ocaml <= 4.01.
  • TSDL – Tsdl is an OCaml module providing thin bindings to the cross-platform SDL library.
  • Lambda-Term74 25 – Lambda-Term is a cross-platform library for manipulating the terminal. It provides an abstraction for keys, mouse events, colors, as well as a set of widgets to write curses-like applications.
  • Notty113 8 - Notty is a declarative terminal library for OCaml, structured around a notion of composable images.



  • dolog20 6 – A dumb OCaml logger.
  • Volt2 1 – A variant of Bolt OCaml logging tool.
  • Logs - Logs provides a logging infrastructure for OCaml.


  • ZeroMQ:
    • ocaml-zmq54 14 – ZeroMQ bindings for OCaml.
    • async-zmq10 2 – Async wrapper around ocaml-zmq.
    • lwt-zmq14 6 – Lwt-friendly interface to ZeroMQ for OCaml.
  • onanomsg28 8 – nanomsg bindings for OCaml.
  • Kafka15 5 – OCaml bindings for Apache Kafka.
  • AMQP20 5 – AMQP client library for Async and Lwt.
  • MPI3 1 – Message Passing Interface bindings for OCaml.
  • MQTT4 0 – OCaml implementation of the MQTT pubsub protocol.


Mobile Applications


  • HTTP Tools:
    • ocaml-cohttp291 125 – Very lightweight HTTP server using Lwt or Async.
    • ocurl25 12 – OCaml bindings to libcurl.
    • httpaf21 3 – A high performance, memory efficient, and scalable web server written in OCaml.
  • ocaml-dns46 32 – A pure OCaml implementation of the DNS protocol.
  • fluent-logger3 0 – Fluentd logger for OCaml.
  • charrua-unix11 2 - charrua-unix is a Unix DHCP daemon based on charrua-core19 4 .

Online Courses

Package Management

  • Distribution:

    • OPAM – A flexible Git-friendly package manager with multiple compiler support.
    • ocamlfind — Local OCaml library manager. Used by most of the OCaml ecosystem.
    • OCaml for Windows - opam repository and experimental build for Windows.
    • makorel6 0 – Release OPAM packages easily.
  • Build Tools:

    • Oasis - A tool to integrate a configure, build and install system in your OCaml project. It helps to create standard entry points in your build system and allows external tools to analyse your project easily.
      • oasis2opam24 9 — Tool to convert OASIS metadata to OPAM package descriptions.
    • obuild59 25 – Simple package build system for ocaml.
    • dune21 1 – A composable and opinionated build system for OCaml (former jbuilder)
    • jenga72 13 – Monadic build system from Jane Street.
    • ocamlbuild — Build system provided with the compiler.
    • ocaml-makefile13 4 — Easy to use Makefile for small to medium-sized OCaml-projects.
    • topkg51 19 — OPAM-aware packaging system using ocamlbuild.
    • Namespaces72 3 - ocamlbuild plugin that converts your directory tree into nested modules.
    • Bazel18 2 - OCaml rules for Bazel, Google's multi-language and platform build tool.


(Note: Sorted from the easier to use to the more flexible.)

  • Libraries:

    • Parmap — Provides easy-to-use parallel map and fold functions.
    • ForkWork10 0 — A simple library for forking child processes to perform work on multiple cores.
    • Functory — A distributed computing library which facilitates distributed execution of parallelizable computations in a seamless fashion.
    • Rpc.Parallel13 0 — A library for spawning processes on a cluster of machines, and passing typed messages between them.
    • Ocamlnet — An enhanced system platform library. Contains the netmulticore library to compute tasks on as many cores of the machine as needed.
    • Nproc23 3 – Process pool implementation for OCaml.
    • Parany2 1 – Parallelize computation over independent items, even if there is an infinite number of them.
    • Sklml – Functional parallel skeleton compiler and programming system for OCaml programs.
  • Articles:


Science and Technical Computing

  • biocaml81 19 – OCaml Bioinformatics Library
  • guizmin3 0 – OCaml library for building bioinformatics pipelines.
  • lacaml - OCaml bindings for BLAS/LAPACK (high-performance linear algebra Fortran libraries).
  • obandit - OCaml library for multi-armed bandits.
  • onumerical4 0 – Numerical library for OCaml.
  • oml80 8 - OCaml library for general numerical work.
  • ocephes1 3 - Bindings to frequently used C special funcitons library.
  • slap48 3 - A linear algebra library in OCaml with type-based static size checking for matrix operations.
  • tensorflow-ocaml111 9 – OCaml bindings for TensorFlow.
  • owl516 46 - OCaml numerical library: dense and sparse matrix, linear algebra, regressions, maths and stats functions.

Regular Expressions

  • Re98 40 – a pure OCaml regular expressions library with combinators, supporting several formats (glob, posix, str...)
  • ocaml-pcre14 2 – bindings to the PCRE library (perl-compatible regular expressions)
  • Humane-re20 2 – Humane-re attempts to provide an easy interface for 90% of your regex needs Courtesy of ocaml-re
  • Tyre91 1 - Tyre is a set of combinators to build type-safe regular expressions, allowing automatic extraction and modification of matched groups.

Security and Cryptography

  • ocaml-tls197 36 – TLS in pure OCaml.
  • Digestif7 3 - Hash algorithms (like SHA* or BLAKE2*) in OCaml and C.
  • cryptokit2 1 – The Cryptokit library for OCaml provides a variety of cryptographic primitives that can be used to implement cryptographic protocols in security-sensitive applications.
  • nocrypto55 26 – A small cryptographic library behind the ocaml-tls project. It is built to be straightforward to use, adhere to functional programming principles and able to run in a Xen-based unikernel.

Note: The differences between nocrypto and cryptokit cryptographic libraries are described in the following blog post: OCaml-TLS: building the nocrypto library core.

Semantic Technology

  • OCaml-RDF – OCaml library to manipulate RDF graphs and execute Sparql queries.


  • bencode3 1 — Bencode (.torrent file format) reader/writer.
  • biniou24 16 – Extensible binary data format, like JSON but faster.
  • jsonm — Non-blocking streaming JSON codec for OCaml.
  • xmlm — A streaming codec to decode and encode the XML data format.
  • yojson79 26 — An optimized parsing and printing library for the JSON format.
  • sexplib62 13 – A S-expression parser and printer

System Programming

  • Mirage OS1k 142 – Mirage is a programming framework for constructing secure, high-performance network applications across a variety of cloud computing and mobile platforms.
  • ocaml-fat10 9 – Read and write FAT format filesystems from OCaml.
  • ocaml-git145 46 – Pure OCaml low-level git bindings.
  • ocaml-vchan26 17 – Pure OCaml implementation of the "vchan" shared-memory communication protocol.


  • Alcotest13 7 – A lightweight and colourful test framework.
  • OUnit – OUnit is a unit test framework for OCaml. It allows one to easily create unit-tests for OCaml code. It is based on HUnit, a unit testing framework for Haskell.
  • QCheck46 9 — QCheck is a property testing library inspired from Haskell's QuickCheck
  • iTeML35 8 (formerly known as qtest) — supports inline pragma's to generate tests.
  • Kaputt — comprehensive testing framework.
  • Pa_test — General inline testing macro's.
  • TestSimple4 0 - A lightweight unit testing framework compatible with the Test Anything Protocol.

Web Development

  • Frameworks:

    • Opium256 28 – Sinatra like web toolkit for OCaml.
    • Ocsigen Eliom – Eliom is a full-featured multi-tier framework, for developing multi-platform Web and mobile apps as 100% OCaml distributed applications. It can also be used for more traditional Web or mobile apps: Web sites, single page applications, REST API, etc.
    • Ohm - Ohm was an open source web framework for the OCaml language which is now dead.
    • webmachine107 12 – A REST toolkit for OCaml. OCaml webmachine is a layer on top of cohttp that implements a state-machine-based HTTP request processor. It's particularly well-suited for writing RESTful APIs. As the name suggests, this is an OCaml port of the webmachine project.
  • Tools:

    • COW77 20 – Caml on the Web (COW) is a set of parsers and syntax extensions to let you manipulate HTML, CSS, XML, JSON and Markdown directly from OCaml code.
    • Ocamlnet has many relevant web libraries — Nethtml html parser, Netasn1 for ASN.1 parsing, Netencoding for Base64, Quoted Printable, URL encoding and HTML escaping, Netmime for MIME processing, etc. See the list of modules in Ocamlnet's manual.
    • tyxml — Library to build valid (according to the W3C spec) Html and Svg trees.
    • js_of_ocaml – Js_of_ocaml is a compiler of OCaml bytecode to Javascript. It makes it possible to run Ocaml programs in a Web browser.
      • commonjs_of_ocaml9 2 - Easily import and export CommonJS modules from a js_of_ocaml project.
    • BuckleScript2k 166 - BuckleScript is backend for OCaml to generate debuggable Javascript. It enables OCaml to integrate Javascript platform in a seamless way.
    • ocaml-uri54 38 – RFC3986 URI parsing library.
    • Goji19 4 – An OCaml bindings generator for JavaScript libraries.
    • Syndic22 8 – RSS and Atom feed parsing
    • ocaml-mustache35 12 – mustache.js logic-less templates in OCaml.
    • atdjs7 0 – atd code generator for OCaml/js_of_ocaml.
    • jingoo52 12 – OCaml template engine almost compatible with jinja2.
    • dispatch19 3 – Path-based dispatching for client- and server-side applications.
    • Lambda Soup139 15 - Functional HTML scraping and manipulation with CSS selectors, à la Python's Beautiful Soup.
    • Markup.ml78 5 - Error-recovering streaming HTML5 and XML parsers, serializers.
    • gen_js_api66 12 - gen_js_api aims at simplifying the creation of OCaml bindings for Javascript libraries.
  • Open Source Projects:

    • Cumulus27 1 – Hacker news like website with the OCaml framework Ocsigen

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