diff --git a/helios-core/build.gradle b/helios-core/build.gradle
index bf117ef..a38cef0 100644
--- a/helios-core/build.gradle
+++ b/helios-core/build.gradle
@@ -13,6 +13,7 @@ dependencies {
 
     testImplementation("io.kotest:kotest-runner-junit5:$kotlinTestVersion")
     testImplementation("io.kotest:kotest-assertions-arrow:$kotlinTestVersion")
+    testImplementation("io.arrow-kt:arrow-test:$arrowVersion")
 
     kaptTest project(":helios-meta")
     kaptTest "io.arrow-kt:arrow-meta:$arrowVersion"
diff --git a/helios-core/src/main/kotlin/helios/core/helios.kt b/helios-core/src/main/kotlin/helios/core/helios.kt
index 07f7d22..5f24a2f 100644
--- a/helios-core/src/main/kotlin/helios/core/helios.kt
+++ b/helios-core/src/main/kotlin/helios/core/helios.kt
@@ -1,7 +1,9 @@
 package helios.core
 
 import arrow.core.*
+import arrow.core.extensions.monoid
 import arrow.core.extensions.option.applicative.applicative
+import arrow.typeclasses.Monoid
 import helios.instances.HeliosFacade
 import helios.instances.jsarray.eq.eq
 import helios.instances.jsnumber.eq.eq
@@ -76,9 +78,6 @@ sealed class Json {
       is JsBoolean -> ifJsBoolean(this)
     }
 
-  fun add(key: String, value: Json): JsObject =
-    JsObject(hashMapOf(key to value))
-
   fun asJsString(): Option<JsString> =
     (this as? JsString)?.some() ?: none()
 
@@ -97,12 +96,7 @@ sealed class Json {
   fun asJsNull(): Option<JsNull> =
     (this as? JsNull)?.some() ?: none()
 
-  fun merge(that: Json): Json =
-    Option.applicative().map(asJsObject(), that.asJsObject()) { (lhs, rhs) ->
-      lhs.toList().fold(rhs) { acc, (key, value) ->
-        rhs[key].fold({ acc.add(key, value) }, { r -> acc.add(key, value.merge(r)) })
-      }
-    }.fix().getOrElse { that }
+  fun merge(that: Json, M: Monoid<Json>): Json = M.combineAll(listOf(this, that))
 
   abstract fun noSpaces(): String
 
@@ -357,7 +351,9 @@ data class JsObject(val value: Map<String, Json>) : Json() {
       JsObject(keyValues.map { it.a to it.b }.toMap())
   }
 
-  fun toList(): List<Tuple2<String, Json>> = value.toList().map { it.first toT it.second }
+  fun add(key: String, value: Json): Json = JsObject(this.value + (key to value))
+
+  fun toList(): List<Tuple2<String, Json>> = value.toList().map { it.toTuple2() }
 
   override fun noSpaces(): String =
     value.map { (k, v) -> """"$k":${v.noSpaces()}""" }.joinToString(
diff --git a/helios-core/src/main/kotlin/helios/instances/instancesEq.kt b/helios-core/src/main/kotlin/helios/instances/instancesEq.kt
index 0c407e5..a030e41 100644
--- a/helios-core/src/main/kotlin/helios/instances/instancesEq.kt
+++ b/helios-core/src/main/kotlin/helios/instances/instancesEq.kt
@@ -10,6 +10,13 @@ import helios.instances.jsnumber.eq.eq
 import helios.instances.jsobject.eq.eq
 import helios.instances.json.eq.eq
 
+@extension
+interface JsStringEq : Eq<JsString> {
+  override fun JsString.eqv(b: JsString): Boolean = with(String.eq()) {
+    value.toString().eqv(b.value.toString())
+  }
+}
+
 @extension
 interface JsObjectEq : Eq<JsObject> {
   override fun JsObject.eqv(b: JsObject): Boolean = with(Json.eq()) {
diff --git a/helios-core/src/main/kotlin/helios/instances/instancesMonoid.kt b/helios-core/src/main/kotlin/helios/instances/instancesMonoid.kt
new file mode 100644
index 0000000..5abd621
--- /dev/null
+++ b/helios-core/src/main/kotlin/helios/instances/instancesMonoid.kt
@@ -0,0 +1,46 @@
+package helios.instances
+
+import arrow.extension
+import arrow.typeclasses.Monoid
+import helios.core.JsArray
+import helios.core.JsDouble
+import helios.core.JsFloat
+import helios.core.JsInt
+import helios.core.JsLong
+import helios.core.JsObject
+import helios.core.JsString
+
+@extension
+interface JsIntMonoid : Monoid<JsInt>, JsIntSemigroup {
+    override fun empty(): JsInt = JsInt(0)
+}
+
+@extension
+interface JsLongMonoid : Monoid<JsLong>, JsLongSemigroup {
+    override fun empty(): JsLong = JsLong(0L)
+}
+
+@extension
+interface JsFloatMonoid : Monoid<JsFloat>, JsFloatSemigroup {
+    override fun empty(): JsFloat = JsFloat(0f)
+}
+
+@extension
+interface JsDoubleMonoid : Monoid<JsDouble>, JsDoubleSemigroup {
+    override fun empty(): JsDouble = JsDouble(0.0)
+}
+
+@extension
+interface JsStringMonoid : Monoid<JsString>, JsStringSemigroup {
+    override fun empty(): JsString = JsString("")
+}
+
+@extension
+interface JsArrayMonoid : Monoid<JsArray>, JsArraySemigroup {
+    override fun empty(): JsArray = JsArray(emptyList())
+}
+
+@extension
+interface JsObjectMonoid : Monoid<JsObject>, JsObjectSemigroup {
+    override fun empty(): JsObject = JsObject(emptyMap())
+}
diff --git a/helios-core/src/main/kotlin/helios/instances/instancesSemigroup.kt b/helios-core/src/main/kotlin/helios/instances/instancesSemigroup.kt
new file mode 100644
index 0000000..d8e0734
--- /dev/null
+++ b/helios-core/src/main/kotlin/helios/instances/instancesSemigroup.kt
@@ -0,0 +1,63 @@
+package helios.instances
+
+import arrow.core.ListK
+import arrow.core.extensions.listk.semigroup.semigroup
+import arrow.core.extensions.semigroup
+import arrow.core.k
+import arrow.extension
+import arrow.typeclasses.Semigroup
+import helios.core.JsArray
+import helios.core.JsDouble
+import helios.core.JsFloat
+import helios.core.JsInt
+import helios.core.JsLong
+import helios.core.JsObject
+import helios.core.JsString
+import helios.core.Json
+
+@extension
+interface JsIntSemigroup : Semigroup<JsInt> {
+    override fun JsInt.combine(b: JsInt): JsInt = JsInt(Int.semigroup().run {
+        value.combine(b.value)
+    })
+}
+
+@extension
+interface JsLongSemigroup : Semigroup<JsLong> {
+    override fun JsLong.combine(b: JsLong): JsLong = JsLong(Long.semigroup().run {
+        value.combine(b.value)
+    })
+}
+
+@extension
+interface JsFloatSemigroup : Semigroup<JsFloat> {
+    override fun JsFloat.combine(b: JsFloat): JsFloat = JsFloat(Float.semigroup().run {
+        value.combine(b.value)
+    })
+}
+
+@extension
+interface JsDoubleSemigroup : Semigroup<JsDouble> {
+    override fun JsDouble.combine(b: JsDouble): JsDouble = JsDouble(Double.semigroup().run {
+        value.combine(b.value)
+    })
+}
+
+@extension
+interface JsStringSemigroup : Semigroup<JsString> {
+    override fun JsString.combine(b: JsString): JsString = JsString(String.semigroup().run {
+        value.toString().combine(b.value.toString())
+    })
+}
+
+@extension
+interface JsArraySemigroup : Semigroup<JsArray> {
+    override fun JsArray.combine(b: JsArray): JsArray = JsArray(ListK.semigroup<Json>().run {
+        value.k().combine(b.value.k())
+    })
+}
+
+@extension
+interface JsObjectSemigroup : Semigroup<JsObject> {
+    override fun JsObject.combine(b: JsObject): JsObject = JsObject(value + b.value)
+}
diff --git a/helios-core/src/test/kotlin/helios/core/MonoidTest.kt b/helios-core/src/test/kotlin/helios/core/MonoidTest.kt
new file mode 100644
index 0000000..f6948ab
--- /dev/null
+++ b/helios-core/src/test/kotlin/helios/core/MonoidTest.kt
@@ -0,0 +1,32 @@
+package helios.core
+
+import arrow.test.UnitSpec
+import arrow.test.laws.MonoidLaws
+import arrow.test.laws.SemigroupLaws
+import helios.instances.jsstring.eq.eq
+import helios.instances.jsstring.monoid.monoid
+import helios.instances.jsstring.semigroup.semigroup
+import io.kotlintest.properties.Gen
+
+class MonoidTest : UnitSpec() {
+
+    init {
+        testLaws(
+            SemigroupLaws.laws(
+                JsString.semigroup(),
+                JsString("a"),
+                JsString("b"),
+                JsString("c"),
+                JsString.eq()
+            )
+        )
+
+        testLaws(
+            MonoidLaws.laws(
+                JsString.monoid(),
+                Gen.string().map { JsString(it) },
+                JsString.eq()
+            )
+        )
+    }
+}
diff --git a/helios-optics/src/test/kotlin/helios/optics/instances.kt b/helios-optics/src/test/kotlin/helios/optics/instances.kt
index a9ec8af..cf0f6da 100644
--- a/helios-optics/src/test/kotlin/helios/optics/instances.kt
+++ b/helios-optics/src/test/kotlin/helios/optics/instances.kt
@@ -1,24 +1,14 @@
 package helios.optics
 
-import arrow.core.None
-import arrow.core.Option
-import arrow.core.extensions.option.eq.eq
+import arrow.typeclasses.Eq
 import helios.arrow.UnitSpec
 import helios.arrow.generators.functionAToB
-import helios.arrow.generators.option
-import helios.arrow.laws.LensLaws
 import helios.arrow.laws.OptionalLaws
 import helios.arrow.laws.TraversalLaws
-import arrow.typeclasses.Eq
-import arrow.typeclasses.Monoid
 import helios.core.JsArray
 import helios.core.JsObject
-import helios.core.Json
-import helios.instances.jsobject.eq.eq
-import helios.instances.json.eq.eq
 import helios.optics.jsarray.each.each
 import helios.optics.jsarray.index.index
-import helios.optics.jsobject.at.at
 import helios.optics.jsobject.each.each
 import helios.optics.jsobject.index.index
 import helios.test.generators.alphaStr
@@ -29,66 +19,52 @@ import io.kotest.properties.Gen
 
 class InstancesTest : UnitSpec() {
 
-  init {
-
-    testLaws(
-      OptionalLaws.laws(
-        optionalGen = Gen.alphaStr().map { JsObject.index().index(it) },
-        aGen = Gen.jsObject(),
-        bGen = Gen.json(),
-        funcGen = Gen.functionAToB(Gen.json()),
-        EQA = Eq.any(),
-        EQOptionB = Eq.any()
-      )
-    )
-
-    testLaws(
-      OptionalLaws.laws(
-        optional = JsArray.index().index(1),
-        aGen = Gen.jsArray(),
-        bGen = Gen.json(),
-        funcGen = Gen.functionAToB(Gen.json()),
-        EQA = Eq.any(),
-        EQOptionB = Eq.any()
-      )
-    )
+    init {
 
-    testLaws(
-      TraversalLaws.laws(
-        traversal = JsObject.each().each(),
-        aGen = Gen.jsObject(),
-        bGen = Gen.json(),
-        funcGen = Gen.functionAToB(Gen.json()),
-        EQA = Eq.any(),
-        EQOptionB = Eq.any(),
-        EQListB = Eq.any()
-      )
-    )
+        testLaws(
+            OptionalLaws.laws(
+                optionalGen = Gen.alphaStr().map { JsObject.index().index(it) },
+                aGen = Gen.jsObject(),
+                bGen = Gen.json(),
+                funcGen = Gen.functionAToB(Gen.json()),
+                EQA = Eq.any(),
+                EQOptionB = Eq.any()
+            )
+        )
 
-    testLaws(
-      TraversalLaws.laws(
-        traversal = JsArray.each().each(),
-        aGen = Gen.jsArray(),
-        bGen = Gen.json(),
-        funcGen = Gen.functionAToB(Gen.json()),
-        EQA = Eq.any(),
-        EQOptionB = Eq.any(),
-        EQListB = Eq.any()
-      )
-    )
+        testLaws(
+            OptionalLaws.laws(
+                optional = JsArray.index().index(1),
+                aGen = Gen.jsArray(),
+                bGen = Gen.json(),
+                funcGen = Gen.functionAToB(Gen.json()),
+                EQA = Eq.any(),
+                EQOptionB = Eq.any()
+            )
+        )
 
-    testLaws(LensLaws.laws(
-      lensGen = Gen.alphaStr().map { JsObject.at().at(it) },
-      aGen = Gen.jsObject(),
-      bGen = Gen.option(Gen.json()),
-      funcGen = Gen.functionAToB(Gen.option(Gen.json())),
-      EQA = JsObject.eq(),
-      EQB = Option.eq(Json.eq()),
-      MB = object : Monoid<Option<Json>> {
-        override fun Option<Json>.combine(b: Option<Json>) = flatMap { a -> b.map { a.merge(it) } }
-        override fun empty(): Option<Json> = None
-      }
-    ))
+        testLaws(
+            TraversalLaws.laws(
+                traversal = JsObject.each().each(),
+                aGen = Gen.jsObject(),
+                bGen = Gen.json(),
+                funcGen = Gen.functionAToB(Gen.json()),
+                EQA = Eq.any(),
+                EQOptionB = Eq.any(),
+                EQListB = Eq.any()
+            )
+        )
 
-  }
+        testLaws(
+            TraversalLaws.laws(
+                traversal = JsArray.each().each(),
+                aGen = Gen.jsArray(),
+                bGen = Gen.json(),
+                funcGen = Gen.functionAToB(Gen.json()),
+                EQA = Eq.any(),
+                EQOptionB = Eq.any(),
+                EQListB = Eq.any()
+            )
+        )
+    }
 }
\ No newline at end of file