diff --git a/backoff/_typing.py b/backoff/_typing.py
index a1e8a88..0159904 100644
--- a/backoff/_typing.py
+++ b/backoff/_typing.py
@@ -1,12 +1,35 @@
 # coding:utf-8
 import logging
-from typing import Any, Callable, Dict, Generator, Sequence, Union, TypeVar
-
+import sys
+from typing import (Any, Callable, Dict, Generator, Sequence, Tuple, Union,
+                    TypeVar)
 
 T = TypeVar("T")
 
+if sys.version_info >= (3, 8):
+    from typing import TypedDict
+else:
+    try:
+        from typing_extensions import TypedDict
+    except ImportError:
+        TypedDict = object
+
+
+class _Details(TypedDict):
+    target: Callable[..., Any]
+    args: Tuple[Any, ...]
+    kwargs: Dict[str, Any]
+    tries: int
+    elapsed: float
+
+
+class Details(_Details, total=False):
+    wait: float  # this key will be present in the on_backoff handler case for either decorator
+    value: Any  # this key will be present in the on_predicate decorator case
+
+
 _CallableT = TypeVar('_CallableT', bound=Callable[..., Any])
-_Handler = Callable[[Dict[str, Any]], None]
+_Handler = Callable[[Details], None]
 _Jitterer = Callable[[float], float]
 _MaybeCallable = Union[T, Callable[[], T]]
 _MaybeLogger = Union[str, logging.Logger]
diff --git a/backoff/types.py b/backoff/types.py
new file mode 100644
index 0000000..25f20a4
--- /dev/null
+++ b/backoff/types.py
@@ -0,0 +1,6 @@
+# coding:utf-8
+from ._typing import Details
+
+__all__ = [
+    'Details'
+]