js_of_ocaml

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Freedom report

Two barsScore 5.4

Free tierA free tier is on its own pricing page
Open codeNo open-source code on record
Runs widely2 of 6 device platforms
DocumentedPlans, terms and facts published

js_of_ocaml is ranked #20 of 28 in code transpilers on Freedom251. It runs on API, Linux, Web. There is a free plan.

js_of_ocaml plans and pricing

All plans

js_of_ocaml Free No paid plans or usage limits stated on the pages reviewed github.com · 9 Oct 2026

Compared on code transpilers

Syntax-version conversion: No
Intermediate output: No
CLI access: Yes
API access: No

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The record

Purpose: Js_of_ocaml compiles OCaml bytecode programs to JavaScript so they can run in browsers and Node.js.
No recompiling libraries: It works with an existing OCaml installation and does not require recompiling libraries.
Browser bindings: The project includes bindings for a large part of browser APIs.
JavaScript interop: Its library provides a typed interface for bridging differences between OCaml and JavaScript values.
Build integration: Dune supports js_of_ocaml natively and selects separate compilation in dev and whole-program compilation in release builds.
Libraries: The distribution includes packages for Lwt support, TyXML, JSON derivation, and running an OCaml toplevel in the browser.
Runtime targets: Generated JavaScript is documented to work with Node.js 18 or later, modern ES2020 browsers, and QuickJS-NG.
Requirements: The documented compiler requirements include OCaml 4.13 to 5.5, Dune 3.20 or later, and Menhir.
Optimization: Whole-program compilation performs global dead-code elimination and cross-module optimizations to produce smaller and faster output.
Limits: Most of the Sys module is unsupported, extra OCaml libraries such as Thread are generally unsupported, and tail calls are not optimized in general.
Security and compliance: The project pages reviewed do not state a security certification or compliance claim.
Support: The project asks users to report problems or questions through GitHub issues and include version details and a minimal reproducible example when possible.
License: The repository lists GPL-2.0-or-later and LGPL-2.1-or-later with the OCaml linking exception as its licenses.
Performance: The project says its benchmarks show generated programs typically run faster than with the OCaml bytecode interpreter.
Price from: Free

Where it ranks on Freedom251

Best Code Transpilers in 2026#20 of 28

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Sources

ocsigen.org/js_of_ocaml/latest/js_of_ocaml/overview· checked 9 Oct 2026
ocsigen.org/js_of_ocaml/latest/js_of_ocaml/javascri· checked 9 Oct 2026
ocsigen.org/js_of_ocaml/latest/js_of_ocaml/compilat· checked 9 Oct 2026
ocsigen.org/js_of_ocaml/latest/js_of_ocaml/api.html· checked 9 Oct 2026
ocsigen.org/js_of_ocaml/latest/js_of_ocaml/install.· checked 9 Oct 2026
ocsigen.org/js_of_ocaml/latest/js_of_ocaml/contribu· checked 9 Oct 2026
github.com/ocsigen/js_of_ocaml/blob/master/js_of_o· checked 9 Oct 2026
github.com/ocsigen/js_of_ocaml· checked 9 Oct 2026
github.com/ocsigen/js_of_ocaml/blob/master/LICENSE· checked 9 Oct 2026