diff --git a/doc/doc.ml b/doc/doc.ml
index 4bda1293..6e9c8d01 100644
--- a/doc/doc.ml
+++ b/doc/doc.ml
@@ -1,5 +1,7 @@
 open Opam_repo_ci
 
+module Opam_version = Opam_ci_check.Opam_version
+module Variant = Opam_ci_check.Variant
 module Git = Current_git
 
 type platform = {
diff --git a/lib/build.ml b/lib/build.ml
index aece828d..567a9fa7 100644
--- a/lib/build.ml
+++ b/lib/build.ml
@@ -2,6 +2,9 @@ open Current.Syntax
 
 module Docker = Current_docker.Default
 module Distro = Dockerfile_opam.Distro
+module Opam_version = Opam_ci_check.Opam_version
+module Variant = Opam_ci_check.Variant
+module Spec = Opam_ci_check.Spec
 
 let master_distro = (Distro.resolve_alias Distro.master_distro :> Distro.t)
 let default_compilers_full = Ocaml_version.Releases.[ v4_14; Ocaml_version.Releases.latest ] (* NOTE: Should probably stay with list length 2 *)
@@ -192,7 +195,7 @@ let get_base ~arch variant =
         Docker.peek ~schedule:weekly ~arch:(Ocaml_version.to_docker_arch arch)
           ("ocaml/opam:" ^ Variant.docker_tag variant)
       in
-      Spec.Docker (Current_docker.Raw.Image.of_hash repo_id)
+      Spec.Docker repo_id
 
 let build (module Builder : Build_intf.S) ~analysis ~pkgopts ~master ~source ~opam_version ~lower_bounds ~revdeps label variant =
   let arch = Variant.arch variant in
diff --git a/lib/build.mli b/lib/build.mli
index c3efcf77..4e518bd0 100644
--- a/lib/build.mli
+++ b/lib/build.mli
@@ -6,7 +6,7 @@ val compilers :
     lower_bounds:bool ->
     revdeps:bool ->
     string ->
-    Variant.t ->
+    Opam_ci_check.Variant.t ->
     'a) ->
   unit ->
   'a list
@@ -18,7 +18,7 @@ val linux_distributions :
     lower_bounds:bool ->
     revdeps:bool ->
     string ->
-    Variant.t ->
+    Opam_ci_check.Variant.t ->
     'a) ->
   'a list
 
@@ -28,7 +28,7 @@ val macos :
     lower_bounds:bool ->
     revdeps:bool ->
     string ->
-    Variant.t ->
+    Opam_ci_check.Variant.t ->
     'a) ->
   'a list
 
@@ -38,17 +38,17 @@ val freebsd :
     lower_bounds:bool ->
     revdeps:bool ->
     string ->
-    Variant.t ->
+    Opam_ci_check.Variant.t ->
     'a) ->
   'a list
 
 val extras :
   build:
-    (opam_version:Opam_version.t ->
+    (opam_version:Opam_ci_check.Opam_version.t ->
     lower_bounds:bool ->
     revdeps:bool ->
     string ->
-    Variant.t ->
+    Opam_ci_check.Variant.t ->
     'a) ->
   'a list
 
diff --git a/lib/build_intf.ml b/lib/build_intf.ml
index efa239ab..563715eb 100644
--- a/lib/build_intf.ml
+++ b/lib/build_intf.ml
@@ -6,8 +6,8 @@ module type S = sig
     whether high- and low-priority jobs are set as urgent. *)
   val v :
     label:string ->
-    spec:Spec.t Current.t ->
-    base:Spec.base Current.t ->
+    spec:Opam_ci_check.Spec.t Current.t ->
+    base:Opam_ci_check.Spec.base Current.t ->
     master:Current_git.Commit.t Current.t ->
     urgent:([`High | `Low] -> bool) option Current.t ->
     Current_git.Commit_id.t Current.t ->
@@ -20,11 +20,11 @@ module type S = sig
       The spec is generated on top of [base], and the OCurrent job is run
       after the job specified by [after], making it a dependency. *)
   val list_revdeps :
-    variant:Variant.t ->
-    opam_version:Opam_version.t ->
+    variant:Opam_ci_check.Variant.t ->
+    opam_version:Opam_ci_check.Opam_version.t ->
     pkgopt:Package_opt.t Current.t ->
     new_pkgs:OpamPackage.t list Current.t ->
-    base:Spec.base Current.t ->
+    base:Opam_ci_check.Spec.base Current.t ->
     master:Current_git.Commit.t Current.t ->
     after:unit Current.t ->
     Current_git.Commit_id.t Current.t ->
diff --git a/lib/cluster_build.ml b/lib/cluster_build.ml
index 5b7d52d8..f151c581 100644
--- a/lib/cluster_build.ml
+++ b/lib/cluster_build.ml
@@ -2,6 +2,9 @@ open Current.Syntax
 open Capnp_rpc_lwt
 open Lwt.Infix
 
+module Variant = Opam_ci_check.Variant
+module Spec = Opam_ci_check.Spec
+module Opam_build = Opam_ci_check.Opam_build
 module Git = Current_git
 
 let ( >>!= ) = Lwt_result.bind
diff --git a/lib/cluster_build.mli b/lib/cluster_build.mli
index 937bdc8a..d5cc8ce1 100644
--- a/lib/cluster_build.mli
+++ b/lib/cluster_build.mli
@@ -14,8 +14,8 @@ val config :
 val v :
   t ->
   label:string ->
-  spec:Spec.t Current.t ->
-  base:Spec.base Current.t ->
+  spec:Opam_ci_check.Spec.t Current.t ->
+  base:Opam_ci_check.Spec.base Current.t ->
   master:Current_git.Commit.t Current.t ->
   urgent:([`High | `Low] -> bool) option Current.t ->
   Current_git.Commit_id.t Current.t ->
@@ -29,11 +29,11 @@ val v :
   the job specified by [after], making it a dependency. *)
 val list_revdeps :
   t ->
-  variant:Variant.t ->
-  opam_version:Opam_version.t ->
+  variant:Opam_ci_check.Variant.t ->
+  opam_version:Opam_ci_check.Opam_version.t ->
   pkgopt:Package_opt.t Current.t ->
   new_pkgs:OpamPackage.t list Current.t ->
-  base:Spec.base Current.t ->
+  base:Opam_ci_check.Spec.base Current.t ->
   master:Current_git.Commit.t Current.t ->
   after:unit Current.t ->
   Current_git.Commit_id.t Current.t ->
diff --git a/lib/dune b/lib/dune
index d4efe65c..03f17d12 100644
--- a/lib/dune
+++ b/lib/dune
@@ -20,4 +20,5 @@
   obuilder-spec
   opam-format
   opam-state
-  opam-repo-ci-api))
+  opam-repo-ci-api
+  opam_ci_check))
diff --git a/lib/local_build.ml b/lib/local_build.ml
index 2a7c1d7c..22ac5de5 100644
--- a/lib/local_build.ml
+++ b/lib/local_build.ml
@@ -1,6 +1,9 @@
 open Current.Syntax
 open Lwt.Infix
 
+module Spec = Opam_ci_check.Spec
+module Variant = Opam_ci_check.Variant
+module Opam_build = Opam_ci_check.Opam_build
 module Git = Current_git
 module Raw = Current_docker.Raw
 
@@ -158,7 +161,7 @@ module Op = struct
           ~os (Opam_build.build_spec ~base ~local:true ~for_docker:true build_config)
     in
     Current.Job.write job
-      (Fmt.str "@[<v>Base: %a@,%a@]@." Raw.Image.pp image Spec.pp_summary ty);
+      (Fmt.str "@[<v>Base: %s@,%a@]@." image Spec.pp_summary ty);
     Current.Job.write job
       (Fmt.str
           "@.To reproduce locally:@.@.cd $(mktemp -d)@.%a@.cat > Dockerfile \
diff --git a/lib/local_build.mli b/lib/local_build.mli
index d86f6743..8e00bd40 100644
--- a/lib/local_build.mli
+++ b/lib/local_build.mli
@@ -5,8 +5,8 @@
     to conform with the interface for [Cluster_build]. *)
 val v :
   label:string ->
-  spec:Spec.t Current.t ->
-  base:Spec.base Current.t ->
+  spec:Opam_ci_check.Spec.t Current.t ->
+  base:Opam_ci_check.Spec.base Current.t ->
   master:Current_git.Commit.t Current.t ->
   urgent:([ `High | `Low ] -> bool) option Current.t ->
   Current_git.Commit_id.t Current.t -> unit Current.t
@@ -19,11 +19,11 @@ val v :
     The spec is generated on top of [base], and the OCurrent job is run after
     the job specified by [after], making it a dependency. *)
 val list_revdeps :
-  variant:Variant.t ->
-  opam_version:Opam_version.t ->
+  variant:Opam_ci_check.Variant.t ->
+  opam_version:Opam_ci_check.Opam_version.t ->
   pkgopt:Package_opt.t Current.t ->
   new_pkgs:OpamPackage.t list Current.t ->
-  base:Spec.base Current.t ->
+  base:Opam_ci_check.Spec.base Current.t ->
   master:Current_git.Commit.t Current.t ->
   after:unit Current.t ->
   Current_git.Commit_id.t Current.t -> OpamPackage.Set.t Current.t
diff --git a/opam-ci-check.opam b/opam-ci-check.opam
index b0b22f0c..c9389e44 100644
--- a/opam-ci-check.opam
+++ b/opam-ci-check.opam
@@ -23,7 +23,11 @@ depends: [
   "sexplib"
   "cmdliner" {>= "1.1.1"}
   "opam-client" {>= "2.3.0~alpha1"}
+  "ocaml-version" {>= "3.6.9"}
+  "obuilder-spec"
   "odoc" {with-doc}
+  "ppx_deriving" {>= "5.2.1"}
+  "ppx_deriving_yojson"
 ]
 build: [
   ["dune" "subst"] {dev}
diff --git a/opam-ci-check/lib/dune b/opam-ci-check/lib/dune
index 38873286..3cdd03af 100644
--- a/opam-ci-check/lib/dune
+++ b/opam-ci-check/lib/dune
@@ -1,4 +1,11 @@
 (library
  (name opam_ci_check)
  (public_name opam-ci-check)
- (libraries opam-client sexplib str))
+ (preprocess
+  (pps ppx_deriving.std ppx_deriving_yojson))
+ (libraries
+  opam-client
+  sexplib
+  str
+  ocaml-version
+  obuilder-spec))
diff --git a/lib/opam_build.ml b/opam-ci-check/lib/opam_build.ml
similarity index 100%
rename from lib/opam_build.ml
rename to opam-ci-check/lib/opam_build.ml
diff --git a/lib/opam_build.mli b/opam-ci-check/lib/opam_build.mli
similarity index 100%
rename from lib/opam_build.mli
rename to opam-ci-check/lib/opam_build.mli
diff --git a/opam-ci-check/lib/opam_ci_check.ml b/opam-ci-check/lib/opam_ci_check.ml
index ae31d9a4..a0fa2697 100644
--- a/opam-ci-check/lib/opam_ci_check.ml
+++ b/opam-ci-check/lib/opam_ci_check.ml
@@ -5,3 +5,7 @@
 module Revdeps = Revdeps
 module Test = Test
 module Lint = Lint
+module Opam_build = Opam_build
+module Variant = Variant
+module Opam_version = Opam_version
+module Spec = Spec
diff --git a/lib/opam_version.ml b/opam-ci-check/lib/opam_version.ml
similarity index 100%
rename from lib/opam_version.ml
rename to opam-ci-check/lib/opam_version.ml
diff --git a/lib/opam_version.mli b/opam-ci-check/lib/opam_version.mli
similarity index 100%
rename from lib/opam_version.mli
rename to opam-ci-check/lib/opam_version.mli
diff --git a/lib/spec.ml b/opam-ci-check/lib/spec.ml
similarity index 94%
rename from lib/spec.ml
rename to opam-ci-check/lib/spec.ml
index fd606349..5cf39dba 100644
--- a/lib/spec.ml
+++ b/opam-ci-check/lib/spec.ml
@@ -1,11 +1,11 @@
 (* TODO: Make macOS use docker images *)
 type base =
-  | Docker of Current_docker.Raw.Image.t
+  | Docker of string
   | Macos of string
   | Freebsd of string
 
 let base_to_string = function
-  | Docker img -> Current_docker.Raw.Image.hash img
+  | Docker img -> img
   | Macos base -> base
   | Freebsd base -> base
 
diff --git a/lib/spec.mli b/opam-ci-check/lib/spec.mli
similarity index 97%
rename from lib/spec.mli
rename to opam-ci-check/lib/spec.mli
index 2d64c020..75e18020 100644
--- a/lib/spec.mli
+++ b/opam-ci-check/lib/spec.mli
@@ -4,7 +4,7 @@
     MacOS and FreeBSD do not yet have Docker images and
     start from custom base images stored in the workers. *)
 type base =
-  | Docker of Current_docker.Raw.Image.t
+  | Docker of string
   | Macos of string
   | Freebsd of string
 
diff --git a/lib/variant.ml b/opam-ci-check/lib/variant.ml
similarity index 100%
rename from lib/variant.ml
rename to opam-ci-check/lib/variant.ml
diff --git a/lib/variant.mli b/opam-ci-check/lib/variant.mli
similarity index 100%
rename from lib/variant.mli
rename to opam-ci-check/lib/variant.mli
diff --git a/test/dune b/test/dune
index 3ef03124..920e784d 100644
--- a/test/dune
+++ b/test/dune
@@ -1,7 +1,12 @@
 (test
  (name test)
  (package opam-repo-ci-service)
- (libraries opam_repo_ci alcotest alcotest-lwt ppx_deriving_yojson.runtime)
+ (libraries
+  opam_ci_check
+  opam_repo_ci
+  alcotest
+  alcotest-lwt
+  ppx_deriving_yojson.runtime)
  (preprocess
   (pps ppx_deriving.eq ppx_deriving_yojson))
  (deps
diff --git a/test/test.ml b/test/test.ml
index 6b1287d0..599142fe 100644
--- a/test/test.ml
+++ b/test/test.ml
@@ -1,7 +1,9 @@
-
-
 open Opam_repo_ci
 
+module Spec = Opam_ci_check.Spec
+module Opam_version = Opam_ci_check.Opam_version
+module Variant = Opam_ci_check.Variant
+module Opam_build = Opam_ci_check.Opam_build
 module Git = Current_git
 
 let specs =