diff --git a/src/core/generator.py b/src/core/generator.py
new file mode 100644
index 0000000..bad0351
--- /dev/null
+++ b/src/core/generator.py
@@ -0,0 +1,376 @@
+"""Response Generator for creating mock responses from JSON Schema."""
+
+import random
+from datetime import date, datetime
+from typing import Any
+
+from faker import Faker
+
+
+class ResponseGeneratorError(Exception):
+    """Base exception for response generator errors."""
+
+    pass
+
+
+class UnsupportedSchemaType(ResponseGeneratorError):
+    """Raised when an unsupported schema type is encountered."""
+
+    pass
+
+
+class ResponseGenerator:
+    """Generates realistic mock responses based on JSON Schema definitions."""
+
+    TYPE_MAPPING = {
+        "string": "string",
+        "integer": "integer",
+        "number": "number",
+        "boolean": "boolean",
+        "array": "array",
+        "object": "object",
+        "null": "null",
+    }
+
+    FORMAT_MAPPING = {
+        "date": "date",
+        "date-time": "date_time",
+        "time": "time",
+        "email": "email",
+        "uri": "uri",
+        "uuid": "uuid",
+        "hostname": "hostname",
+        "ipv4": "ipv4",
+        "ipv6": "ipv6",
+        "password": "password",
+    }
+
+    def __init__(self, seed: int | None = None) -> None:
+        """Initialize the response generator.
+
+        Args:
+            seed: Optional seed for reproducible random generation.
+        """
+        self.faker = Faker()
+        if seed is not None:
+            Faker.seed(seed)
+            random.seed(seed)
+
+    def generate(self, schema: dict[str, Any]) -> Any:
+        """Generate a mock value based on the given schema.
+
+        Args:
+            schema: JSON Schema definition.
+
+        Returns:
+            Generated mock value.
+
+        Raises:
+            UnsupportedSchemaType: If the schema type is not supported.
+        """
+        if not schema:
+            return None
+
+        schema_type = schema.get("type")
+
+        if schema_type is None and "$ref" in schema:
+            return self._resolve_ref(schema["$ref"], schema)
+
+        if schema_type is None:
+            return None
+
+        type_key = schema_type.lower()
+        if type_key not in self.TYPE_MAPPING:
+            raise UnsupportedSchemaType(f"Unsupported schema type: {schema_type}")
+
+        generator_method = getattr(
+            self, f"_generate_{type_key}", self._generate_default
+        )
+        return generator_method(schema)
+
+    def _generate_string(self, schema: dict[str, Any]) -> str:
+        """Generate a string value based on the schema.
+
+        Args:
+            schema: String schema definition.
+
+        Returns:
+            Generated string value.
+        """
+        fmt = schema.get("format", "")
+        pattern = schema.get("pattern")
+
+        if fmt and fmt.lower() in self.FORMAT_MAPPING:
+            format_method_name = self.FORMAT_MAPPING[fmt.lower()]
+            format_method = getattr(self.faker, format_method_name, None)
+            if format_method:
+                return format_method()
+
+        if pattern:
+            return self._generate_by_pattern(pattern)
+
+        min_length = schema.get("minLength", 0)
+        max_length = schema.get("maxLength", 100)
+        enum_values = schema.get("enum")
+
+        if enum_values:
+            return random.choice(enum_values)
+
+        actual_max = max(min_length, max_length)
+        length = random.randint(min_length, actual_max) if actual_max > 0 else 10
+        length = max(length, 5)
+
+        return self.faker.text(max_nb_chars=length)
+
+    def _generate_by_pattern(self, pattern: str) -> str:
+        """Generate a string matching a regex pattern.
+
+        Args:
+            pattern: Regex pattern.
+
+        Returns:
+            Generated string matching the pattern.
+        """
+        if pattern == r"^[a-zA-Z0-9_-]{1,50}$":
+            return self.faker.slug()
+
+        return self.faker.word()
+
+    def _generate_integer(self, schema: dict[str, Any]) -> int:
+        """Generate an integer value based on the schema.
+
+        Args:
+            schema: Integer schema definition.
+
+        Returns:
+            Generated integer value.
+        """
+        minimum = schema.get("minimum", 0)
+        maximum = schema.get("maximum", 1000)
+        multiple_of = schema.get("multipleOf", 1)
+
+        value = random.randint(minimum, maximum)
+
+        if multiple_of > 1:
+            value = (value // multiple_of) * multiple_of
+
+        return value
+
+    def _generate_number(self, schema: dict[str, Any]) -> float:
+        """Generate a number value based on the schema.
+
+        Args:
+            schema: Number schema definition.
+
+        Returns:
+            Generated number value.
+        """
+        minimum = schema.get("minimum", 0.0)
+        maximum = schema.get("maximum", 1000.0)
+        multiple_of = schema.get("multipleOf", 1.0)
+
+        value = random.uniform(minimum, maximum)
+
+        if multiple_of > 1:
+            value = round(value / multiple_of) * multiple_of
+
+        return round(value, 2)
+
+    def _generate_boolean(self, schema: dict[str, Any]) -> bool:
+        """Generate a boolean value based on the schema.
+
+        Args:
+            schema: Boolean schema definition.
+
+        Returns:
+            Generated boolean value.
+        """
+        return random.choice([True, False])
+
+    def _generate_array(self, schema: dict[str, Any]) -> list[Any]:
+        """Generate an array based on the schema.
+
+        Args:
+            schema: Array schema definition.
+
+        Returns:
+            Generated array of values.
+        """
+        items_schema = schema.get("items", {})
+        min_items = schema.get("minItems", 0)
+        max_items = schema.get("maxItems", 10)
+        enum_values = schema.get("enum")
+
+        count = random.randint(min_items, max_items)
+
+        if enum_values:
+            return [random.choice(enum_values) for _ in range(count)]
+
+        return [self.generate(items_schema) for _ in range(count)]
+
+    def _generate_object(self, schema: dict[str, Any]) -> dict[str, Any]:
+        """Generate an object based on the schema.
+
+        Args:
+            schema: Object schema definition.
+
+        Returns:
+            Generated object as a dictionary.
+        """
+        properties = schema.get("properties", {})
+        required_fields = schema.get("required", [])
+        additional_properties = schema.get("additionalProperties", True)
+
+        result: dict[str, Any] = {}
+
+        for prop_name, prop_schema in properties.items():
+            if prop_name in required_fields or additional_properties:
+                value = self.generate(prop_schema)
+                result[prop_name] = self._convert_datetime(value)
+
+        return result
+
+    def _convert_datetime(self, value: Any) -> Any:
+        """Convert datetime objects to ISO format strings.
+
+        Args:
+            value: The value to convert.
+
+        Returns:
+            Converted value.
+        """
+        if isinstance(value, datetime):
+            return value.isoformat()
+        elif isinstance(value, date):
+            return value.isoformat()
+        return value
+
+    def _generate_null(self, schema: dict[str, Any]) -> None:
+        """Generate a null value.
+
+        Args:
+            schema: Null schema definition.
+
+        Returns:
+            None.
+        """
+        return None
+
+    def _generate_default(self, schema: dict[str, Any]) -> Any:
+        """Default generator for unknown types.
+
+        Args:
+            schema: Schema definition.
+
+        Returns:
+            None as default value.
+        """
+        return None
+
+    def _resolve_ref(
+        self, ref: str, schema: dict[str, Any]
+    ) -> Any:
+        """Resolve a $ref reference.
+
+        Args:
+            ref: The reference string.
+            schema: The current schema containing the reference.
+
+        Returns:
+            The resolved value.
+        """
+        if ref.startswith("#/components/schemas/"):
+            ref_name = ref.split("/")[-1]
+            return schema.get("resolved_schemas", {}).get(ref_name, {})
+
+        return None
+
+    def set_resolved_schemas(
+        self, schemas: dict[str, Any]
+    ) -> None:
+        """Set resolved schema references.
+
+        Args:
+            schemas: Dictionary of resolved schema names to schema objects.
+        """
+        self._resolved_schemas = schemas
+
+    def generate_response(
+        self,
+        schema: dict[str, Any],
+        status_code: int = 200,
+        headers: dict[str, str] | None = None,
+    ) -> dict[str, Any]:
+        """Generate a complete HTTP response.
+
+        Args:
+            schema: Response schema definition.
+            status_code: HTTP status code.
+            headers: Optional response headers.
+
+        Returns:
+            Complete response dictionary.
+        """
+        response_body = self.generate(schema)
+
+        response: dict[str, Any] = {
+            "status_code": status_code,
+            "body": response_body,
+        }
+
+        if headers:
+            response["headers"] = headers
+
+        return response
+
+    def generate_list_response(
+        self,
+        item_schema: dict[str, Any],
+        count: int | None = None,
+        status_code: int = 200,
+    ) -> dict[str, Any]:
+        """Generate a list/array response.
+
+        Args:
+            item_schema: Schema for array items.
+            count: Number of items to generate (random if not specified).
+            status_code: HTTP status code.
+
+        Returns:
+            Complete response with array body.
+        """
+        if count is None:
+            count = random.randint(1, 10)
+
+        items = [self.generate(item_schema) for _ in range(count)]
+
+        return {
+            "status_code": status_code,
+            "body": items,
+        }
+
+    def generate_error_response(
+        self,
+        message: str,
+        status_code: int = 400,
+        error_type: str = "Bad Request",
+    ) -> dict[str, Any]:
+        """Generate an error response.
+
+        Args:
+            message: Error message.
+            status_code: HTTP status code.
+            error_type: Type of error.
+
+        Returns:
+            Error response dictionary.
+        """
+        return {
+            "status_code": status_code,
+            "body": {
+                "error": {
+                    "type": error_type,
+                    "message": message,
+                }
+            },
+        }