diff --git a/core/src/main/java/com/google/adk/tools/FunctionCallingUtils.java b/core/src/main/java/com/google/adk/tools/FunctionCallingUtils.java
index eec115127..3244b40e9 100644
--- a/core/src/main/java/com/google/adk/tools/FunctionCallingUtils.java
+++ b/core/src/main/java/com/google/adk/tools/FunctionCallingUtils.java
@@ -45,7 +45,7 @@
 public final class FunctionCallingUtils {
 
   private static final Logger logger = LoggerFactory.getLogger(FunctionCallingUtils.class);
-  private static final ObjectMapper objectMapper = JsonBaseModel.getMapper();
+  private static final ObjectMapper defaultObjectMapper = JsonBaseModel.getMapper();
 
   /** Holds the state during a single schema generation process to handle caching and recursion. */
   private static class SchemaGenerationContext {
@@ -162,7 +162,20 @@ private static Schema buildSchemaFromParameter(Parameter param) {
    * @throws IllegalArgumentException if a type is encountered that cannot be serialized by Jackson.
    */
   public static Schema buildSchemaFromType(Type type) {
-    return buildSchemaRecursive(objectMapper.constructType(type), new SchemaGenerationContext());
+    return buildSchemaFromType(type, defaultObjectMapper);
+  }
+
+  /**
+   * Builds a Schema from a Java Type, creating a new context for the generation process.
+   *
+   * @param type The Java {@link Type} to convert into a Schema.
+   * @param objectMapper The {@link ObjectMapper} to use for introspecting types.
+   * @return The generated {@link Schema}.
+   * @throws IllegalArgumentException if a type is encountered that cannot be serialized by Jackson.
+   */
+  public static Schema buildSchemaFromType(Type type, ObjectMapper objectMapper) {
+    return buildSchemaRecursive(
+        objectMapper.constructType(type), new SchemaGenerationContext(), objectMapper);
   }
 
   /**
@@ -173,7 +186,8 @@ public static Schema buildSchemaFromType(Type type) {
    * @return The generated {@link Schema}.
    * @throws IllegalArgumentException if a type is encountered that cannot be serialized by Jackson.
    */
-  private static Schema buildSchemaRecursive(JavaType javaType, SchemaGenerationContext context) {
+  private static Schema buildSchemaRecursive(
+      JavaType javaType, SchemaGenerationContext context, ObjectMapper objectMapper) {
     if (context.isProcessing(javaType)) {
       logger.warn("Type {} is recursive. Omitting from schema.", javaType.toCanonical());
       return Schema.builder()
@@ -194,7 +208,9 @@ private static Schema buildSchemaRecursive(JavaType javaType, SchemaGenerationCo
       Class<?> rawClass = javaType.getRawClass();
 
       if (javaType.isCollectionLikeType() && List.class.isAssignableFrom(rawClass)) {
-        builder.type("ARRAY").items(buildSchemaRecursive(javaType.getContentType(), context));
+        builder
+            .type("ARRAY")
+            .items(buildSchemaRecursive(javaType.getContentType(), context, objectMapper));
       } else if (javaType.isMapLikeType()) {
         builder.type("OBJECT");
       } else if (String.class.equals(rawClass)) {
@@ -232,7 +248,8 @@ private static Schema buildSchemaRecursive(JavaType javaType, SchemaGenerationCo
         for (BeanPropertyDefinition property : beanDescription.findProperties()) {
           AnnotatedMember member = property.getPrimaryMember();
           if (member != null) {
-            properties.put(property.getName(), buildSchemaRecursive(member.getType(), context));
+            properties.put(
+                property.getName(), buildSchemaRecursive(member.getType(), context, objectMapper));
             if (property.isRequired()) {
               required.add(property.getName());
             }
diff --git a/core/src/main/java/com/google/adk/tools/FunctionTool.java b/core/src/main/java/com/google/adk/tools/FunctionTool.java
index a6167ee46..40046aa30 100644
--- a/core/src/main/java/com/google/adk/tools/FunctionTool.java
+++ b/core/src/main/java/com/google/adk/tools/FunctionTool.java
@@ -44,12 +44,13 @@
 public class FunctionTool extends BaseTool {
 
   private static final Logger logger = LoggerFactory.getLogger(FunctionTool.class);
-  private static final ObjectMapper objectMapper = JsonBaseModel.getMapper();
+  private static final ObjectMapper defaultObjectMapper = JsonBaseModel.getMapper();
 
   private final @Nullable Object instance;
   private final Method func;
   private final FunctionDeclaration funcDeclaration;
   private final boolean requireConfirmation;
+  private final ObjectMapper objectMapper;
 
   public static FunctionTool create(Object instance, Method func) {
     return create(instance, func, /* requireConfirmation= */ false);
@@ -166,11 +167,25 @@ private static boolean wasCompiledWithDefaultParameterNames(Method func) {
   }
 
   protected FunctionTool(@Nullable Object instance, Method func, boolean isLongRunning) {
-    this(instance, func, isLongRunning, /* requireConfirmation= */ false);
+    this(instance, func, isLongRunning, /* requireConfirmation= */ false, defaultObjectMapper);
   }
 
   protected FunctionTool(
       @Nullable Object instance, Method func, boolean isLongRunning, boolean requireConfirmation) {
+    this(instance, func, isLongRunning, requireConfirmation, defaultObjectMapper);
+  }
+
+  protected FunctionTool(
+      @Nullable Object instance, Method func, boolean isLongRunning, ObjectMapper objectMapper) {
+    this(instance, func, isLongRunning, /* requireConfirmation= */ false, objectMapper);
+  }
+
+  protected FunctionTool(
+      @Nullable Object instance,
+      Method func,
+      boolean isLongRunning,
+      boolean requireConfirmation,
+      ObjectMapper objectMapper) {
     super(
         func.isAnnotationPresent(Annotations.Schema.class)
                 && !func.getAnnotation(Annotations.Schema.class).name().isEmpty()
@@ -193,6 +208,7 @@ protected FunctionTool(
         FunctionCallingUtils.buildFunctionDeclaration(
             this.func, ImmutableList.of("toolContext", "inputStream"));
     this.requireConfirmation = requireConfirmation;
+    this.objectMapper = objectMapper;
   }
 
   @Override
@@ -365,7 +381,7 @@ private static Class<?> getTypeClass(Type type, String paramName) {
     }
   }
 
-  private static List<Object> createList(List<Object> values, Class<?> type) {
+  private List<Object> createList(List<Object> values, Class<?> type) {
     List<Object> list = new ArrayList<>();
     // List of parameterized type is not supported.
     if (type == null) {
@@ -387,7 +403,7 @@ private static List<Object> createList(List<Object> values, Class<?> type) {
     return list;
   }
 
-  private static Object castValue(Object value, Class<?> type) {
+  private Object castValue(Object value, Class<?> type) {
     if (type.equals(Integer.class) || type.equals(int.class)) {
       if (value instanceof Integer) {
         return value;