diff --git a/src/scaffoldfitter/fitterjson.py b/src/scaffoldfitter/fitterjson.py
new file mode 100644
index 0000000..74b64cc
--- /dev/null
+++ b/src/scaffoldfitter/fitterjson.py
@@ -0,0 +1,23 @@
+"""
+Factory function for constructing FitterStep types from JSON Dict.
+"""
+from scaffoldfitter.fitter import Fitter
+from scaffoldfitter.fitterstepalign import FitterStepAlign
+from scaffoldfitter.fitterstepfit import FitterStepFit
+
+
+def decodeJSONFitterSteps(fitter : Fitter, dct):
+    """
+    Function for passing as decoder to Fitter.decodeSettingsJSON().
+    Constructs scaffold objects from their JSON object encoding.
+    Used as object_hook argument to json.loads as a lambda function
+    to pass fitter:
+    lambda dct: decodeJSONFitterSteps(fitter, dct)
+    :param fitter: Owning Fitter object for new FitterSteps.
+    """
+    for FitterStepType in [ FitterStepAlign, FitterStepFit ]:
+        if FitterStepType.getJsonTypeId() in dct:
+            fitterStep = FitterStepType(fitter)
+            fitterStep.decodeSettingsJSONDict(dct)
+            return fitterStep
+    return dct