Irmin is an OCaml library for building mergeable, branchable distributed data stores.

Built-in snapshotting

Built-in snapshotting

Backup and restore your data at any point in time.

Storage agnostic

Storage agnostic

You can use Irmin on top of your own storage layer.

Custom datatypes

Custom datatypes

Automatic (de)serialization for custom data types.

Highly portable

Highly portable

Runs anywhere from Linux to web browsers and Xen unikernels.

Git compatibility

Git compatibility

Bi-directional compatibility with the Git on-disk format. Irmin state can be inspected and modified using the Git command-line tool.

Dynamic behavior

Dynamic behavior

Allows users to define custom merge functions and create event-driven workflows using a notification mechanism.


To install Irmin, the command-line tool and all optional dependencies using opam:

$ opam install irmin-cli

A minimal installation, with only the in-memory storage backend can be installed by running:

$ opam install irmin

The following packages have been made available on opam:

  • irmin - the base package, including an in-memory storage implementation
  • irmin-chunk - chunked storage
  • irmin-fs - filesystem-based storage
  • irmin-git - Git compatible storage
  • irmin-pack - pack-file based storage
  • irmin-http - a simple REST interface
  • irmin-graphql - a GraphQL server
  • irmin-mirage - mirage compatibility
  • irmin-cli - command line tool
  • libirmin - C bindings to the irmin API

For more information about an individual package consult the online documentation.


Below is a simple example of setting a key and getting the value out of a Git based, filesystem-backed store.

open Lwt.Syntax

(* Irmin store with string contents *)
module Store = Irmin_git_unix.FS.KV(Irmin.Contents.String)

(* Database configuration *)
let config = Irmin_git.config ~bare:true "/tmp/irmin/test"

(* Commit author *)
let author = "Example "

(* Commit information *)
let info fmt = ~author fmt

let main =
  (* Open the repo *)
  let* repo = Store.Repo.v config in

  (* Load the main branch *)
  let* t = Store.main repo in

  (* Set key "foo/bar" to "testing 123" *)
  let* () = Store.set_exn t ~info:(info "Updating foo/bar") ["foo"; "bar"] "testing 123" in

  (* Get key "foo/bar" and print it to stdout *)
  let+ x = Store.get t ["foo"; "bar"] in
  Printf.printf "foo/bar => '%s'\n" x

(* Run the program *)
let () = main

The example is contained in examples/ It can be compiled and executed with dune:

$ dune build examples/readme.exe
$ dune exec examples/readme.exe
foo/bar => 'testing 123'

The examples directory contains more advanced examples, which can be executed in the same way.


The same thing can also be accomplished using irmin, the command-line application installed with irmin-cli, by running:

$ echo "root: ." > irmin.yml
$ irmin init
$ irmin set foo/bar "testing 123"
$ irmin get foo/bar

irmin.yml allows for irmin flags to be set on a per-directory basis. You can also set flags globally using $HOME/.irmin/config.yml.

Run irmin help irmin.yml for further details.

Explore further

Tutorial Issues License

Irmin is part of the MirageOS project and is supported by Tarides, Robur and OCaml Labs.