diff --git a/test_libs/fuzzing/decoder.py b/test_libs/fuzzing/decoder.py
new file mode 100644
index 000000000..16d798f6f
--- /dev/null
+++ b/test_libs/fuzzing/decoder.py
@@ -0,0 +1,84 @@
+from eth2spec.utils.ssz import ssz_typing as spec_ssz
+import ssz
+
+
+def translate_typ(typ) -> ssz.BaseSedes:
+    """
+    Translates a spec type to a Py-SSZ type description (sedes).
+    :param typ: The spec type, a class.
+    :return: The Py-SSZ equivalent.
+    """
+    if spec_ssz.is_container_type(typ):
+        return ssz.Container(
+            [(field_name, translate_typ(field_typ)) for (field_name, field_typ) in typ.get_fields()])
+    elif spec_ssz.is_bytesn_type(typ):
+        return ssz.ByteVector(typ.length)
+    elif spec_ssz.is_bytes_type(typ):
+        return ssz.ByteList()
+    elif spec_ssz.is_vector_type(typ):
+        return ssz.Vector(translate_typ(spec_ssz.read_vector_elem_type(typ)), typ.length)
+    elif spec_ssz.is_list_type(typ):
+        return ssz.List(translate_typ(spec_ssz.read_list_elem_type(typ)))
+    elif spec_ssz.is_bool_type(typ):
+        return ssz.boolean
+    elif spec_ssz.is_uint_type(typ):
+        size = spec_ssz.uint_byte_size(typ)
+        if size == 1:
+            return ssz.uint8
+        elif size == 2:
+            return ssz.uint16
+        elif size == 4:
+            return ssz.uint32
+        elif size == 8:
+            return ssz.uint64
+        elif size == 16:
+            return ssz.uint128
+        elif size == 32:
+            return ssz.uint256
+        else:
+            raise TypeError("invalid uint size")
+    else:
+        raise Exception("Type not supported: {}".format(typ))
+
+
+def translate_value(value, typ):
+    """
+    Translate a value output from Py-SSZ deserialization into the given spec type.
+    :param value: The PySSZ value
+    :param typ: The type from the spec to translate into
+    :return: the translated value
+    """
+    if spec_ssz.is_uint_type(typ):
+        size = spec_ssz.uint_byte_size(typ)
+        if size == 1:
+            return spec_ssz.uint8(value)
+        elif size == 2:
+            return spec_ssz.uint16(value)
+        elif size == 4:
+            return spec_ssz.uint32(value)
+        elif size == 8:
+            # uint64 is default (TODO this is changing soon)
+            return value
+        elif size == 16:
+            return spec_ssz.uint128(value)
+        elif size == 32:
+            return spec_ssz.uint256(value)
+        else:
+            raise TypeError("invalid uint size")
+    elif spec_ssz.is_list_type(typ):
+        elem_typ = spec_ssz.read_elem_type(typ)
+        return [translate_value(elem, elem_typ) for elem in value]
+    elif spec_ssz.is_bool_type(typ):
+        return False
+    elif spec_ssz.is_vector_type(typ):
+        elem_typ = spec_ssz.read_elem_type(typ)
+        return typ(translate_value(elem, elem_typ) for elem in value)
+    elif spec_ssz.is_bytesn_type(typ):
+        return typ(value)
+    elif spec_ssz.is_bytes_type(typ):
+        return value
+    elif spec_ssz.is_container_type(typ):
+        return typ(**{f_name: translate_value(f_val, f_typ) for (f_name, f_val, f_typ)
+                      in zip(typ.get_field_names(), value.values(), typ.get_field_types())})
+    else:
+        raise Exception("Type not supported: {}".format(typ))
diff --git a/test_libs/fuzzing/requirements.txt b/test_libs/fuzzing/requirements.txt
new file mode 100644
index 000000000..98dcd9564
--- /dev/null
+++ b/test_libs/fuzzing/requirements.txt
@@ -0,0 +1,3 @@
+../../test_libs/pyspec
+../../test_libs/config_helpers
+ssz==0.1.0a8