diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 840e80e..f1de8da 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,6 +17,9 @@ jobs:
       - uses: actions/setup-python@v5
         with:
           python-version: '3.12.5'
+      - uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: latest
 
       - name: Install uv
         run: pipx install uv
diff --git a/Makefile b/Makefile
index ed8ceaa..bcf0c53 100644
--- a/Makefile
+++ b/Makefile
@@ -35,6 +35,10 @@ define docker_run
 				@sed -i 's/$$/,$(.SHELLSTATUS)/' $@
 endef
 
+schemas/%/schema-2020-12.json: \
+	schemas/%/schema.json
+	bunx alterschema --from draft4 --to 2020-12 $< > $@
+
 # JSON Toolkit
 
 implementations/jsontoolkit/.dockertimestamp: \
@@ -134,3 +138,22 @@ dist/results/go-jsonschema/%: \
 	schemas/%/instances.jsonl \
 	| dist/results/go-jsonschema
 	@$(call docker_run,go-jsonschema,/workspace/$(dir $(word 2,$^)))
+
+# MJS
+
+implementations/mjs/.dockertimestamp: \
+	implementations/mjs/build.sbt \
+	implementations/mjs/Benchmark.scala \
+	implementations/mjs/project/build.properties \
+	implementations/mjs/project/plugins.sbt \
+	implementations/mjs/Dockerfile
+	docker build -t jsonschema-benchmark/mjs implementations/mjs
+	touch $@
+
+dist/results/mjs/%: \
+	implementations/mjs/.dockertimestamp \
+	schemas/%/schema-2020-12.json \
+	schemas/%/instances.jsonl \
+	| dist/results/mjs
+	@$(call docker_run,mjs,/workspace/$(word 2,$^) /workspace/$(word 3,$^))
+
diff --git a/implementations/mjs/Benchmark.scala b/implementations/mjs/Benchmark.scala
new file mode 100644
index 0000000..12bf025
--- /dev/null
+++ b/implementations/mjs/Benchmark.scala
@@ -0,0 +1,28 @@
+import main.MainClass
+
+import scala.io.Source
+
+object Benchmark {
+  def main(args: Array[String]): Unit = {
+    if (args.length != 2) {
+      System.exit(1)
+    }
+    val schemaPath = args(0)
+    val instancePath = args(1)
+
+    val schema = Source.fromFile(schemaPath).mkString
+    val registryMap = Map.empty[String, String]
+
+    val start = System.nanoTime()
+    for (instance <- Source.fromFile(instancePath).getLines()) {
+      val result = MainClass.validateInstance(schema, instance, registryMap)
+      if (!result) {
+        System.err.println("Invalid instance")
+        System.exit(1)
+      }
+    }
+    val finish = System.nanoTime()
+
+    println((finish - start).toString)
+  }
+}
diff --git a/implementations/mjs/Dockerfile b/implementations/mjs/Dockerfile
new file mode 100644
index 0000000..29555d0
--- /dev/null
+++ b/implementations/mjs/Dockerfile
@@ -0,0 +1,9 @@
+FROM sbtscala/scala-sbt:eclipse-temurin-17.0.4_1.7.2_2.13.10 AS builder
+
+WORKDIR /app
+COPY Benchmark.scala /app
+COPY build.sbt /app
+COPY project /app/project
+RUN sbt assembly
+ENTRYPOINT ["java", "-jar", "/app/target/scala-2.13/benchmarkMjs.jar"]
+CMD []
diff --git a/implementations/mjs/build.sbt b/implementations/mjs/build.sbt
new file mode 100644
index 0000000..c5c4d12
--- /dev/null
+++ b/implementations/mjs/build.sbt
@@ -0,0 +1,29 @@
+name := "mjs-validator"
+
+ThisBuild / version := "1.0"
+ThisBuild / scalaVersion := "2.13.10"
+
+javacOptions ++= Seq("-source", "17", "-target", "17")
+
+resolvers += Resolver.mavenCentral
+
+libraryDependencies ++= Seq(
+  "org.scala-lang" % "scala-library" % "2.13.10"
+)
+
+val mjsVersion = "v0.1.0"
+lazy val mjs = RootProject(
+  uri(s"https://gitlab.lip6.fr/jsonschema/modernjsonschemavalidator.git#$mjsVersion")
+)
+lazy val benchmarkMjs = (project in file(".")).dependsOn(mjs)
+assembly / assemblyJarName := "benchmarkMjs.jar"
+assembly / packageOptions := Seq(
+  Package.ManifestAttributes(
+    "Main-Class" -> "Benchmark",
+    "Implementation-Group" -> "org.up.mjs",
+    "Implementation-Name" -> "mjs",
+    "Implementation-Version" -> mjsVersion
+  )
+)
+
+scalacOptions += "-Ymacro-annotations"
diff --git a/implementations/mjs/project/build.properties b/implementations/mjs/project/build.properties
new file mode 100644
index 0000000..2743082
--- /dev/null
+++ b/implementations/mjs/project/build.properties
@@ -0,0 +1 @@
+sbt.version=1.9.6
diff --git a/implementations/mjs/project/plugins.sbt b/implementations/mjs/project/plugins.sbt
new file mode 100644
index 0000000..d83c883
--- /dev/null
+++ b/implementations/mjs/project/plugins.sbt
@@ -0,0 +1 @@
+addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "2.1.5")
diff --git a/implementations/mjs/version.sh b/implementations/mjs/version.sh
new file mode 100755
index 0000000..6b40408
--- /dev/null
+++ b/implementations/mjs/version.sh
@@ -0,0 +1,6 @@
+#!/bin/sh
+
+set -o errexit
+set -o nounset
+
+grep '^val mjsVersion =' implementations/mjs/build.sbt | cut -d= -f2 | tr -d '" '