diff --git a/gui/src/app/Project/ProjectDataModel.ts b/gui/src/app/Project/ProjectDataModel.ts
index e85ef8f..23eab70 100644
--- a/gui/src/app/Project/ProjectDataModel.ts
+++ b/gui/src/app/Project/ProjectDataModel.ts
@@ -90,13 +90,24 @@ const isProjectBase = (x: any): x is ProjectBase => {
   return true;
 };
 
+export enum DataSource {
+  GENERATED_BY_R = "generated_by_r",
+  GENERATED_BY_PYTHON = "generated_by_python",
+}
+
 type ProjectMetadata = {
   title: string;
+  dataSource?: DataSource;
 };
 
 export const isProjectMetaData = (x: any): x is ProjectMetadata => {
   if (!baseObjectCheck(x)) return false;
   if (typeof x.title !== "string") return false;
+  if (
+    x.dataSource !== undefined && // allow undefined for backwards compatibility
+    !Object.values(DataSource).includes(x.dataSource)
+  )
+    return false;
   return true;
 };
 
@@ -128,7 +139,7 @@ export const isProjectDataModel = (x: any): x is ProjectDataModel => {
 export type ProjectPersistentDataModel = Omit<ProjectDataModel, "ephemera">;
 
 export const initialDataModel: ProjectDataModel = {
-  meta: { title: "Untitled" },
+  meta: { title: "Untitled", dataSource: undefined },
   ephemera: {
     stanFileContent: "",
     dataFileContent: "",
diff --git a/gui/src/app/Project/ProjectReducer.ts b/gui/src/app/Project/ProjectReducer.ts
index 4a2945d..032d8cd 100644
--- a/gui/src/app/Project/ProjectReducer.ts
+++ b/gui/src/app/Project/ProjectReducer.ts
@@ -1,5 +1,6 @@
 import { FieldsContentsMap } from "@SpCore/FileMapping";
 import {
+  DataSource,
   initialDataModel,
   ProjectDataModel,
   ProjectKnownFiles,
@@ -24,6 +25,7 @@ export type ProjectReducerAction =
       type: "retitle";
       title: string;
     }
+  | { type: "setDataSource"; dataSource: DataSource | undefined }
   | {
       type: "editFile";
       content: string;
@@ -81,6 +83,9 @@ const ProjectReducer = (s: ProjectDataModel, a: ProjectReducerAction) => {
     case "clear": {
       return initialDataModel;
     }
+    case "setDataSource": {
+      return { ...s, meta: { ...s.meta, dataSource: a.dataSource } };
+    }
     default:
       return unreachable(a);
   }
diff --git a/gui/src/app/Project/ProjectSerialization.ts b/gui/src/app/Project/ProjectSerialization.ts
index c9cfd10..1912466 100644
--- a/gui/src/app/Project/ProjectSerialization.ts
+++ b/gui/src/app/Project/ProjectSerialization.ts
@@ -112,7 +112,7 @@ const loadMetaFromString = (
   json: string,
   clearExisting: boolean = false,
 ): ProjectDataModel => {
-  const newMeta = JSON.parse(json);
+  let newMeta = JSON.parse(json);
   if (!isProjectMetaData(newMeta)) {
     throw Error("Deserialized meta is not valid");
   }
diff --git a/gui/src/app/Scripting/DataGeneration/DataPyWindow.tsx b/gui/src/app/Scripting/DataGeneration/DataPyWindow.tsx
index bd6f524..4f2f8bf 100644
--- a/gui/src/app/Scripting/DataGeneration/DataPyWindow.tsx
+++ b/gui/src/app/Scripting/DataGeneration/DataPyWindow.tsx
@@ -22,7 +22,7 @@ const handleHelp = () =>
   );
 
 const DataPyWindow: FunctionComponent<Props> = () => {
-  const { consoleRef, status, onStatus, onData } = useDataGenState();
+  const { consoleRef, status, onStatus, onData } = useDataGenState("python");
 
   const callbacks = useMemo(
     () => ({
diff --git a/gui/src/app/Scripting/DataGeneration/DataRWindow.tsx b/gui/src/app/Scripting/DataGeneration/DataRWindow.tsx
index b383932..d37ae26 100644
--- a/gui/src/app/Scripting/DataGeneration/DataRWindow.tsx
+++ b/gui/src/app/Scripting/DataGeneration/DataRWindow.tsx
@@ -19,7 +19,7 @@ const handleHelp = () =>
   );
 
 const DataRWindow: FunctionComponent<Props> = () => {
-  const { consoleRef, status, onStatus, onData } = useDataGenState();
+  const { consoleRef, status, onStatus, onData } = useDataGenState("r");
 
   const { run } = useWebR({ consoleRef, onStatus, onData });
   const handleRun = useCallback(
diff --git a/gui/src/app/Scripting/DataGeneration/useDataGenState.ts b/gui/src/app/Scripting/DataGeneration/useDataGenState.ts
index 892d859..25c74cc 100644
--- a/gui/src/app/Scripting/DataGeneration/useDataGenState.ts
+++ b/gui/src/app/Scripting/DataGeneration/useDataGenState.ts
@@ -1,12 +1,12 @@
 import { useCallback, useContext, useRef, useState } from "react";
-import { ProjectKnownFiles } from "@SpCore/ProjectDataModel";
+import { DataSource, ProjectKnownFiles } from "@SpCore/ProjectDataModel";
 import { writeConsoleOutToDiv } from "@SpScripting/OutputDivUtils";
 import { InterpreterStatus } from "@SpScripting/InterpreterTypes";
 import { ProjectContext } from "@SpCore/ProjectContextProvider";
 
 // A custom hook to share logic between the Python and R data generation windows
 // This contains the output div ref, the interpreter state, and the callback to update the data.
-const useDataGenState = () => {
+const useDataGenState = (source: "python" | "r") => {
   const [status, setStatus] = useState<InterpreterStatus>("idle");
   const consoleRef = useRef<HTMLDivElement>(null);
 
@@ -26,6 +26,13 @@ const useDataGenState = () => {
           filename: ProjectKnownFiles.DATAFILE,
         });
         update({ type: "commitFile", filename: ProjectKnownFiles.DATAFILE });
+        update({
+          type: "setDataSource",
+          dataSource:
+            source === "python"
+              ? DataSource.GENERATED_BY_PYTHON
+              : DataSource.GENERATED_BY_R,
+        });
         // Use "stan-playground" prefix to distinguish from console output of the running code
         writeConsoleOutToDiv(
           consoleRef,
diff --git a/gui/src/app/pages/HomePage/HomePage.tsx b/gui/src/app/pages/HomePage/HomePage.tsx
index 6e1ffa5..b1202c9 100644
--- a/gui/src/app/pages/HomePage/HomePage.tsx
+++ b/gui/src/app/pages/HomePage/HomePage.tsx
@@ -8,6 +8,7 @@ import TextEditor from "@SpComponents/TextEditor";
 import { FileNames } from "@SpCore/FileMapping";
 import { ProjectContext } from "@SpCore/ProjectContextProvider";
 import {
+  DataSource,
   modelHasUnsavedChanges,
   ProjectKnownFiles,
 } from "@SpCore/ProjectDataModel";
@@ -17,12 +18,15 @@ import DataPyWindow from "@SpScripting/DataGeneration/DataPyWindow";
 import DataRWindow from "@SpScripting/DataGeneration/DataRWindow";
 import {
   FunctionComponent,
+  useCallback,
   useContext,
   useEffect,
+  useMemo,
   useRef,
   useState,
 } from "react";
 import SamplingWindow from "./SamplingWindow/SamplingWindow";
+import { ToolbarItem } from "@SpComponents/ToolBar";
 
 type Props = {
   //
@@ -92,6 +96,7 @@ type LeftViewProps = {
 
 const LeftView: FunctionComponent<LeftViewProps> = () => {
   const { data, update } = useContext(ProjectContext);
+
   return (
     <Split horizontal>
       <StanFileEditor
@@ -114,31 +119,73 @@ const LeftView: FunctionComponent<LeftViewProps> = () => {
         }
         readOnly={false}
       />
-      <TextEditor
-        language="json"
-        label={FileNames.DATAFILE}
-        text={data.dataFileContent}
-        onSaveText={() =>
-          update({
-            type: "commitFile",
-            filename: ProjectKnownFiles.DATAFILE,
-          })
-        }
-        editedText={data.ephemera.dataFileContent}
-        onSetEditedText={(content: string) =>
-          update({
-            type: "editFile",
-            content,
-            filename: ProjectKnownFiles.DATAFILE,
-          })
-        }
-        readOnly={false}
-        contentOnEmpty={"Enter JSON data or use the data generation tab"}
-      />
+      <DataEditor />
     </Split>
   );
 };
 
+const DataEditor: FunctionComponent<{}> = () => {
+  const { data, update } = useContext(ProjectContext);
+
+  const dataIsEdited = useMemo(() => {
+    return data.dataFileContent !== data.ephemera.dataFileContent;
+  }, [data.dataFileContent, data.ephemera.dataFileContent]);
+
+  const dataMessage: ToolbarItem[] = useMemo(() => {
+    if (data.meta.dataSource === undefined || dataIsEdited) {
+      return [];
+    } else {
+      return [
+        {
+          type: "text",
+          label:
+            "Data is generated by data." +
+            (data.meta.dataSource === DataSource.GENERATED_BY_PYTHON
+              ? "py"
+              : "R"),
+          color: "info.main",
+        },
+      ];
+    }
+  }, [data.meta.dataSource, dataIsEdited]);
+
+  const onSetEditedText = useCallback(
+    (content: string) => {
+      update({
+        type: "editFile",
+        content,
+        filename: ProjectKnownFiles.DATAFILE,
+      });
+    },
+    [update],
+  );
+
+  const onSaveText = useCallback(() => {
+    update({
+      type: "commitFile",
+      filename: ProjectKnownFiles.DATAFILE,
+    });
+    update({
+      type: "setDataSource",
+      dataSource: undefined,
+    });
+  }, [update]);
+
+  return (
+    <TextEditor
+      language="json"
+      label={FileNames.DATAFILE}
+      text={data.dataFileContent}
+      onSaveText={onSaveText}
+      editedText={data.ephemera.dataFileContent}
+      onSetEditedText={onSetEditedText}
+      readOnly={false}
+      toolbarItems={dataMessage}
+      contentOnEmpty={"Enter JSON data or use the data generation tab"}
+    />
+  );
+};
+
 // adapted from https://mui.com/material-ui/react-drawer/#persistent-drawer
 const MovingBox = styled(Box, {
   shouldForwardProp: (prop) => prop !== "open",
diff --git a/gui/test/app/Project/ProjectDataModel.test.ts b/gui/test/app/Project/ProjectDataModel.test.ts
index 73dc7e7..1783488 100644
--- a/gui/test/app/Project/ProjectDataModel.test.ts
+++ b/gui/test/app/Project/ProjectDataModel.test.ts
@@ -1,4 +1,5 @@
 import {
+  DataSource,
   defaultSamplingOpts,
   exportedForTesting,
   getStringKnownFileKeys,
@@ -248,6 +249,23 @@ describe("Project data model type guards", () => {
       expect(isProjectMetaData({ title: 6 })).toBe(false);
       expect(isProjectMetaData({ no_title: "title" })).toBe(false);
     });
+    test("Returns true for valid data source", () => {
+      expect(
+        isProjectMetaData({
+          title: "title",
+          dataSource: DataSource.GENERATED_BY_PYTHON,
+        }),
+      ).toBe(true);
+      expect(
+        isProjectMetaData({
+          title: "title",
+          dataSource: DataSource.GENERATED_BY_R,
+        }),
+      ).toBe(true);
+    });
+    test("Returns false on bad data source", () => {
+      expect(isProjectMetaData({ title: "title", dataSource: 1 })).toBe(false);
+    });
   });
   describe("Project ephemeral-data typeguard", () => {
     test("Returns true for valid project files object", () => {