diff --git a/services/core/java/com/android/server/integrity/model/AtomicFormula.java b/services/core/java/com/android/server/integrity/model/AtomicFormula.java
index 70ab98c86cda3..9a0553d7aa0c7 100644
--- a/services/core/java/com/android/server/integrity/model/AtomicFormula.java
+++ b/services/core/java/com/android/server/integrity/model/AtomicFormula.java
@@ -46,12 +46,12 @@ public abstract class AtomicFormula implements Formula {
 
     @IntDef(
             value = {
-                    PACKAGE_NAME,
-                    APP_CERTIFICATE,
-                    INSTALLER_NAME,
-                    INSTALLER_CERTIFICATE,
-                    VERSION_CODE,
-                    PRE_INSTALLED,
+                PACKAGE_NAME,
+                APP_CERTIFICATE,
+                INSTALLER_NAME,
+                INSTALLER_CERTIFICATE,
+                VERSION_CODE,
+                PRE_INSTALLED,
             })
     @Retention(RetentionPolicy.SOURCE)
     public @interface Key {}
@@ -60,11 +60,47 @@ public abstract class AtomicFormula implements Formula {
     @Retention(RetentionPolicy.SOURCE)
     public @interface Operator {}
 
+    /**
+     * Package name of the app.
+     *
+     * <p>Can only be used in {@link StringAtomicFormula}.
+     */
     public static final int PACKAGE_NAME = 0;
+
+    /**
+     * SHA-256 of the app certificate of the app.
+     *
+     * <p>Can only be used in {@link StringAtomicFormula}.
+     */
     public static final int APP_CERTIFICATE = 1;
+
+    /**
+     * Package name of the installer. Will be empty string if installed by the system (e.g., adb).
+     *
+     * <p>Can only be used in {@link StringAtomicFormula}.
+     */
     public static final int INSTALLER_NAME = 2;
+
+    /**
+     * SHA-256 of the cert of the installer. Will be empty string if installed by the system (e.g.,
+     * adb).
+     *
+     * <p>Can only be used in {@link StringAtomicFormula}.
+     */
     public static final int INSTALLER_CERTIFICATE = 3;
+
+    /**
+     * Version code of the app.
+     *
+     * <p>Can only be used in {@link IntAtomicFormula}.
+     */
     public static final int VERSION_CODE = 4;
+
+    /**
+     * If the app is pre-installed on the device.
+     *
+     * <p>Can only be used in {@link BooleanAtomicFormula}.
+     */
     public static final int PRE_INSTALLED = 5;
 
     public static final int EQ = 0;
@@ -91,7 +127,7 @@ public abstract class AtomicFormula implements Formula {
          * specified by {@code key} is of the correct relationship to {@code value} as specified by
          * {@code operator}.
          *
-         * @throws IllegalArgumentException if {@code key} is not {@link #VERSION_CODE}
+         * @throws IllegalArgumentException if {@code key} cannot be used with integer value
          */
         public IntAtomicFormula(@Key int key, @Operator int operator, int value) {
             super(key);
@@ -142,6 +178,11 @@ public abstract class AtomicFormula implements Formula {
             }
         }
 
+        @Override
+        public int getTag() {
+            return Formula.INT_ATOMIC_FORMULA_TAG;
+        }
+
         @Override
         public String toString() {
             return String.format(
@@ -157,7 +198,9 @@ public abstract class AtomicFormula implements Formula {
                 return false;
             }
             IntAtomicFormula that = (IntAtomicFormula) o;
-            return getKey() == that.getKey() && mValue == that.mValue;
+            return getKey() == that.getKey()
+                    && mValue == that.mValue
+                    && mOperator == that.mOperator;
         }
 
         @Override
@@ -206,8 +249,7 @@ public abstract class AtomicFormula implements Formula {
          * <p>This formula will hold if and only if the corresponding information of an install
          * specified by {@code key} equals {@code value}.
          *
-         * @throws IllegalArgumentException if {@code key} is not one of {@link #PACKAGE_NAME},
-         *     {@link #APP_CERTIFICATE}, {@link #INSTALLER_NAME} and {@link #INSTALLER_CERTIFICATE}
+         * @throws IllegalArgumentException if {@code key} cannot be used with string value
          */
         public StringAtomicFormula(@Key int key, @NonNull String value) {
             super(key);
@@ -246,6 +288,11 @@ public abstract class AtomicFormula implements Formula {
             return metadataValue.equals(mValue);
         }
 
+        @Override
+        public int getTag() {
+            return Formula.STRING_ATOMIC_FORMULA_TAG;
+        }
+
         @Override
         public String toString() {
             return String.format("(%s %s %s)", keyToString(getKey()), operatorToString(EQ), mValue);
@@ -279,6 +326,7 @@ public abstract class AtomicFormula implements Formula {
             dest.writeStringNoHelper(mValue);
         }
 
+        @NonNull
         public String getValue() {
             return mValue;
         }
@@ -310,7 +358,7 @@ public abstract class AtomicFormula implements Formula {
          * <p>This formula will hold if and only if the corresponding information of an install
          * specified by {@code key} equals {@code value}.
          *
-         * @throws IllegalArgumentException if {@code key} is not {@link #PRE_INSTALLED}
+         * @throws IllegalArgumentException if {@code key} cannot be used with boolean value
          */
         public BooleanAtomicFormula(@Key int key, boolean value) {
             super(key);
@@ -346,6 +394,11 @@ public abstract class AtomicFormula implements Formula {
             return metadataValue == mValue;
         }
 
+        @Override
+        public int getTag() {
+            return Formula.BOOLEAN_ATOMIC_FORMULA_TAG;
+        }
+
         @Override
         public String toString() {
             return String.format("(%s %s %s)", keyToString(getKey()), operatorToString(EQ), mValue);
@@ -398,7 +451,7 @@ public abstract class AtomicFormula implements Formula {
         return mKey;
     }
 
-    String keyToString(int key) {
+    static String keyToString(int key) {
         switch (key) {
             case PACKAGE_NAME:
                 return "PACKAGE_NAME";
@@ -417,7 +470,7 @@ public abstract class AtomicFormula implements Formula {
         }
     }
 
-    String operatorToString(int op) {
+    static String operatorToString(int op) {
         switch (op) {
             case EQ:
                 return "EQ";
diff --git a/services/core/java/com/android/server/integrity/model/Formula.java b/services/core/java/com/android/server/integrity/model/Formula.java
index 852ece536f313..67698277800f5 100644
--- a/services/core/java/com/android/server/integrity/model/Formula.java
+++ b/services/core/java/com/android/server/integrity/model/Formula.java
@@ -16,6 +16,7 @@
 
 package com.android.server.integrity.model;
 
+import android.annotation.IntDef;
 import android.annotation.NonNull;
 import android.annotation.SystemApi;
 import android.os.Parcel;
@@ -26,6 +27,9 @@ import com.android.server.integrity.model.AtomicFormula.BooleanAtomicFormula;
 import com.android.server.integrity.model.AtomicFormula.IntAtomicFormula;
 import com.android.server.integrity.model.AtomicFormula.StringAtomicFormula;
 
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
 /**
  * Represents a rule logic/content.
  *
@@ -34,6 +38,15 @@ import com.android.server.integrity.model.AtomicFormula.StringAtomicFormula;
 @SystemApi
 @VisibleForTesting
 public interface Formula {
+    @IntDef(
+            value = {
+                    OPEN_FORMULA_TAG,
+                    STRING_ATOMIC_FORMULA_TAG,
+                    INT_ATOMIC_FORMULA_TAG,
+                    BOOLEAN_ATOMIC_FORMULA_TAG
+            })
+    @Retention(RetentionPolicy.SOURCE)
+    public @interface Tag {}
 
     int OPEN_FORMULA_TAG = 0;
     int STRING_ATOMIC_FORMULA_TAG = 1;
@@ -46,6 +59,9 @@ public interface Formula {
      */
     boolean isSatisfied(@NonNull AppInstallMetadata appInstallMetadata);
 
+    /** Returns the tag that identifies the current class. */
+    @Tag int getTag();
+
     /**
      * Write a {@link Formula} to {@link android.os.Parcel}.
      *
@@ -55,21 +71,8 @@ public interface Formula {
      * @throws IllegalArgumentException if {@link Formula} is not a recognized subclass
      */
     static void writeToParcel(@NonNull Formula formula, @NonNull Parcel dest, int flags) {
-        if (formula instanceof OpenFormula) {
-            dest.writeInt(OPEN_FORMULA_TAG);
-            ((OpenFormula) formula).writeToParcel(dest, flags);
-        } else if (formula instanceof StringAtomicFormula) {
-            dest.writeInt(STRING_ATOMIC_FORMULA_TAG);
-            ((StringAtomicFormula) formula).writeToParcel(dest, flags);
-        } else if (formula instanceof IntAtomicFormula) {
-            dest.writeInt(INT_ATOMIC_FORMULA_TAG);
-            ((IntAtomicFormula) formula).writeToParcel(dest, flags);
-        } else if (formula instanceof BooleanAtomicFormula) {
-            dest.writeInt(BOOLEAN_ATOMIC_FORMULA_TAG);
-            ((BooleanAtomicFormula) formula).writeToParcel(dest, flags);
-        } else {
-            throw new IllegalArgumentException("Unrecognized class " + formula.getClass());
-        }
+        dest.writeInt(formula.getTag());
+        ((Parcelable) formula).writeToParcel(dest, flags);
     }
 
     /**
diff --git a/services/core/java/com/android/server/integrity/model/OpenFormula.java b/services/core/java/com/android/server/integrity/model/OpenFormula.java
index f29706adeebbc..7a3600f7a4fef 100644
--- a/services/core/java/com/android/server/integrity/model/OpenFormula.java
+++ b/services/core/java/com/android/server/integrity/model/OpenFormula.java
@@ -63,7 +63,7 @@ public final class OpenFormula implements Formula, Parcelable {
     public static final int NOT = 2;
 
     private final @Connector int mConnector;
-    private final List<Formula> mFormulas;
+    private final @NonNull List<Formula> mFormulas;
 
     @NonNull
     public static final Creator<OpenFormula> CREATOR =
@@ -99,6 +99,7 @@ public final class OpenFormula implements Formula, Parcelable {
         for (int i = 0; i < length; i++) {
             mFormulas.add(Formula.readFromParcel(in));
         }
+        validateFormulas(mConnector, mFormulas);
     }
 
     public @Connector int getConnector() {
@@ -127,6 +128,11 @@ public final class OpenFormula implements Formula, Parcelable {
         }
     }
 
+    @Override
+    public int getTag() {
+        return Formula.OPEN_FORMULA_TAG;
+    }
+
     @Override
     public String toString() {
         StringBuilder sb = new StringBuilder();
@@ -175,7 +181,7 @@ public final class OpenFormula implements Formula, Parcelable {
         }
     }
 
-    private void validateFormulas(@Connector int connector, List<Formula> formulas) {
+    private static void validateFormulas(@Connector int connector, List<Formula> formulas) {
         switch (connector) {
             case AND:
             case OR:
@@ -195,7 +201,7 @@ public final class OpenFormula implements Formula, Parcelable {
         }
     }
 
-    private String connectorToString(int connector) {
+    private static String connectorToString(int connector) {
         switch (connector) {
             case AND:
                 return "AND";
diff --git a/services/core/java/com/android/server/integrity/model/Rule.java b/services/core/java/com/android/server/integrity/model/Rule.java
index 14dcb26d10256..f87e4e875eef4 100644
--- a/services/core/java/com/android/server/integrity/model/Rule.java
+++ b/services/core/java/com/android/server/integrity/model/Rule.java
@@ -58,7 +58,7 @@ public final class Rule implements Parcelable {
      */
     public static final int FORCE_ALLOW = 1;
 
-    private final Formula mFormula;
+    private final @NonNull Formula mFormula;
     private final @Effect int mEffect;
 
     public Rule(@NonNull Formula formula, @Effect int effect) {
@@ -119,7 +119,7 @@ public final class Rule implements Parcelable {
             return false;
         }
         Rule that = (Rule) o;
-        return Objects.equals(mFormula, that.mFormula) && mEffect == that.mEffect;
+        return mEffect == that.mEffect && Objects.equals(mFormula, that.mFormula);
     }
 
     @Override
@@ -127,7 +127,7 @@ public final class Rule implements Parcelable {
         return Objects.hash(mFormula, mEffect);
     }
 
-    private String effectToString(int effect) {
+    private static String effectToString(int effect) {
         switch (effect) {
             case DENY:
                 return "DENY";
diff --git a/services/tests/servicestests/src/com/android/server/integrity/serializer/RuleXmlSerializerTest.java b/services/tests/servicestests/src/com/android/server/integrity/serializer/RuleXmlSerializerTest.java
index a256271559502..77886c89c4165 100644
--- a/services/tests/servicestests/src/com/android/server/integrity/serializer/RuleXmlSerializerTest.java
+++ b/services/tests/servicestests/src/com/android/server/integrity/serializer/RuleXmlSerializerTest.java
@@ -297,6 +297,11 @@ public class RuleXmlSerializerTest {
                 return false;
             }
 
+            @Override
+            public int getTag() {
+                return 0;
+            }
+
             @Override
             public int hashCode() {
                 return super.hashCode();