diff --git a/examples/developer-tools/src/backwards_compatibility.ts b/examples/developer-tools/src/backwards_compatibility.ts
index 3a3a46845a..2d2b94b41d 100644
--- a/examples/developer-tools/src/backwards_compatibility.ts
+++ b/examples/developer-tools/src/backwards_compatibility.ts
@@ -37,6 +37,10 @@ const CONNECTION_CHECK_SHADOW = {
 export function convertBaseBlock(
   oldBlock: Blockly.serialization.blocks.State,
 ): Blockly.serialization.blocks.State {
+  if (oldBlock.type !== 'factory_base') {
+    throw Error('Malformed block data');
+  }
+
   const newBlock = {...oldBlock};
   // extraState from the old tool isn't relevant.
   delete newBlock.extraState;
diff --git a/examples/developer-tools/src/controller.ts b/examples/developer-tools/src/controller.ts
index 3c33669587..bb4bf7945f 100644
--- a/examples/developer-tools/src/controller.ts
+++ b/examples/developer-tools/src/controller.ts
@@ -6,13 +6,16 @@
 
 import * as Blockly from 'blockly';
 import * as storage from './storage';
-import {createNewBlock, loadBlock} from './serialization';
+import {createNewBlock, loadBlock, loadBlockFromData} from './serialization';
 import {ViewModel} from './view_model';
 import {JavascriptDefinitionGenerator} from './output-generators/javascript_definition_generator';
 import {JsonDefinitionGenerator} from './output-generators/json_definition_generator';
 import {CodeHeaderGenerator} from './output-generators/code_header_generator';
 import {Menu} from '@material/web/menu/menu';
 import {GeneratorStubGenerator} from './output-generators/generator_stub_generator';
+import {convertBaseBlock} from './backwards_compatibility';
+
+const IMPORT_BLOCK_FACTORY_ID = 'Import from block factory...';
 
 /**
  * This class handles updating the UI output, including refreshing the block preview,
@@ -51,6 +54,33 @@ export class Controller {
       this.handleLoadButton();
     });
 
+    this.viewModel.fileModalCloseButton.addEventListener('click', () => {
+      this.viewModel.toggleFileUploadModal(false);
+    });
+
+    this.viewModel.fileDropZone.addEventListener('drop', (e) => {
+      this.handleFileDrop(e);
+    });
+
+    this.viewModel.fileUploadInput.addEventListener('change', () => {
+      this.handleFileUpload();
+    });
+
+    this.viewModel.fileLabel.addEventListener('keydown', function (ev) {
+      // Clicks the file input if you hit enter on the label for the input
+      if (ev.key === 'Enter') (ev.target as HTMLElement).click();
+    });
+
+    this.viewModel.fileDropZone.addEventListener('dragover', (ev) => {
+      ev.preventDefault();
+      this.viewModel.fileDropZone.classList.add('isDragging');
+    });
+
+    this.viewModel.fileDropZone.addEventListener('dragleave', (ev) => {
+      ev.preventDefault();
+      this.viewModel.fileDropZone.classList.remove('isDragging');
+    });
+
     // Load previously-saved settings once on page load
     this.loadBlockFactorySettings();
   }
@@ -210,6 +240,10 @@ export class Controller {
   private handleLoadSelect(e: Event) {
     if (e.target && e.target instanceof HTMLElement) {
       const blockName = e.target.getAttribute('data-id');
+      if (blockName === IMPORT_BLOCK_FACTORY_ID) {
+        this.handleLoadFromFile();
+        return;
+      }
       loadBlock(this.mainWorkspace, blockName);
     }
   }
@@ -222,7 +256,9 @@ export class Controller {
    */
   private populateLoadMenu() {
     const menuEl = this.viewModel.loadMenu;
-    const newItems = Array.from(storage.getAllSavedBlockNames()).map((name) => {
+    const optionNames = Array.from(storage.getAllSavedBlockNames());
+    optionNames.push(IMPORT_BLOCK_FACTORY_ID);
+    const newItems = optionNames.map((name) => {
       const el = document.createElement('md-menu-item');
       el.setAttribute('data-id', name);
       const div = document.createElement('div');
@@ -236,4 +272,73 @@ export class Controller {
     });
     menuEl.replaceChildren(...newItems);
   }
+
+  /** Shows the file upload modal when the user selects that option from the load menu. */
+  private handleLoadFromFile() {
+    this.viewModel.toggleFileUploadModal(true);
+  }
+
+  /**
+   * Handles the drag event that occurs when a user drops a file onto the file upload
+   * drag-n-drop zone. Gets the first file of the type we want and attempts to load it
+   * into the block factory editor.
+   *
+   * @param e drop event
+   */
+  private handleFileDrop(e: DragEvent) {
+    // Prevent default behavior (Prevent file from being opened)
+    e.preventDefault();
+
+    this.viewModel.toggleFileUploadWarning(false);
+
+    this.viewModel.fileDropZone.classList.remove('isDragging');
+
+    if (!e.dataTransfer.items) return;
+
+    const firstItem = [...e.dataTransfer.items].find((item) => {
+      // Get the first plain text file, in case the user uploaded multiple
+      if (item.kind === 'file' && item.type === 'text/plain') {
+        return true;
+      }
+    });
+
+    if (!firstItem) {
+      this.viewModel.toggleFileUploadWarning(true);
+      return;
+    }
+    this.loadFromFile(firstItem.getAsFile());
+  }
+
+  /**
+   * Handles the event that occurs when a user picks a file from the file input.
+   * Attempts to load the file into the block factory editor.
+   */
+  private handleFileUpload() {
+    this.viewModel.toggleFileUploadWarning(false);
+    const input = this.viewModel.fileUploadInput as HTMLInputElement;
+    const file = input.files[0];
+    if (!file) return;
+    this.loadFromFile(file);
+  }
+
+  /**
+   * Given a file, tries to run it through our backwards-compatibility converter
+   * and load the block into block factory. If there's an error at any point,
+   * we show a warning and allow the user to try the upload again.
+   *
+   * @param file File containing the block json to load. This should be the file
+   *    downloaded directly from the old block factory tool.
+   */
+  private loadFromFile(file: File) {
+    file
+      .text()
+      .then((contents) => {
+        const fixedBlockData = convertBaseBlock(JSON.parse(contents));
+        loadBlockFromData(this.mainWorkspace, fixedBlockData);
+        this.viewModel.toggleFileUploadModal(false);
+      })
+      .catch((e) => {
+        this.viewModel.toggleFileUploadWarning(true);
+      });
+  }
 }
diff --git a/examples/developer-tools/src/index.css b/examples/developer-tools/src/index.css
index 3d48bd6bc6..7997e55d00 100644
--- a/examples/developer-tools/src/index.css
+++ b/examples/developer-tools/src/index.css
@@ -1,3 +1,7 @@
+:root {
+  --md-dialog-container-color: white;
+}
+
 body {
   margin: 0;
 }
@@ -83,6 +87,54 @@ md-menu {
   max-height: 430px;
 }
 
+#file-upload-drop-zone {
+  background-color: white;
+  outline: 2px dashed #2bb4ca;
+  outline-offset: -10px;
+  border-radius: 8px;
+  min-height: 200px;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+}
+
+#file-upload-drop-zone > * {
+  flex-grow: 0;
+  margin: 12px 24px;
+}
+#file-upload-drop-zone > span {
+  font-size: 48px;
+}
+
+#file-upload-drop-zone.isDragging {
+  background-color: rgba(0, 0, 0, 0.1);
+}
+
+#file-label {
+  font-weight: 700;
+  cursor: pointer;
+}
+
+.warning-message {
+  visibility: hidden;
+  color: #b00020;
+  text-align: center;
+}
+
+/* Hides an element visually but not from screen readers */
+.visually-hidden {
+  position: absolute !important;
+  width: 1px !important;
+  height: 1px !important;
+  padding: 0 !important;
+  margin: -1px !important;
+  overflow: hidden !important;
+  clip: rect(0, 0, 0, 0) !important;
+  white-space: nowrap !important;
+  border: 0 !important;
+}
+
 @media screen and (max-width: 900px) {
   #block-factory-container {
     flex-direction: column;
diff --git a/examples/developer-tools/src/index.html b/examples/developer-tools/src/index.html
index 864a7494d4..647f38561c 100644
--- a/examples/developer-tools/src/index.html
+++ b/examples/developer-tools/src/index.html
@@ -4,6 +4,9 @@
     <meta charset="utf-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>Blockly Developer Tools</title>
+    <link
+      rel="stylesheet"
+      href="https://fonts.googleapis.com/css2?family=Google+Symbols:opsz,wght,FILL,GRAD@48,400,0,0" />
   </head>
   <body>
     <div class="page-container">
@@ -22,6 +25,41 @@
         <button id="delete-btn" class="btn">Delete</button>
       </div>
       <div id="block-factory-container">
+        <md-dialog id="file-upload-modal">
+          <div slot="headline">Import from Block Factory</div>
+          <div slot="content">
+            <p>
+              You can upload a file from the legacy Block Factory to import that
+              block here.
+            </p>
+            <div id="file-upload-drop-zone">
+              <span class="google-symbols" aria-hidden="true">upload_file</span>
+              <input
+                type="file"
+                id="file-upload"
+                class="visually-hidden"
+                accept=".txt" />
+              <p>
+                <label for="file-upload" id="file-label" tabindex="1">
+                  Choose a file
+                </label>
+                or drag it here
+              </p>
+              <p id="file-upload-warning" class="warning-message">
+                File could not be parsed. Make sure you're uploading the file
+                you downloaded from the legacy Block Factory.
+              </p>
+            </div>
+          </div>
+          <div slot="actions">
+            <md-text-button
+              id="file-upload-close"
+              form="form-id"
+              value="cancel">
+              Cancel
+            </md-text-button>
+          </div>
+        </md-dialog>
         <div id="main-workspace"></div>
         <div id="output-pane" class="panel-container">
           <div id="block-preview"></div>
diff --git a/examples/developer-tools/src/serialization.ts b/examples/developer-tools/src/serialization.ts
index 126a2e12ae..dcafb48646 100644
--- a/examples/developer-tools/src/serialization.ts
+++ b/examples/developer-tools/src/serialization.ts
@@ -59,6 +59,30 @@ export function loadBlock(workspace: Blockly.Workspace, blockName?: string) {
   }
 }
 
+/**
+ * Loads given block json into the given workspace.
+ *
+ * @param workspace Blockly workspace to load into.
+ * @param blockJson Block json to load. This is state representing a single block,
+ *    not the entire workspace.
+ */
+export function loadBlockFromData(
+  workspace: Blockly.Workspace,
+  blockJson: Blockly.serialization.blocks.State,
+) {
+  // Disable events so we don't save while deleting blocks.
+  Blockly.Events.disable();
+  workspace.clear();
+  Blockly.Events.enable();
+
+  // There might be conflicts when loading a block from a file.
+  // If so, find a similar unused name so we don't overwrite.
+  const blockName = getNewUnusedName(blockJson.fields.NAME);
+  blockJson.fields.NAME = blockName;
+
+  Blockly.serialization.blocks.append(blockJson, workspace);
+}
+
 /**
  * Creates a new block from scratch.
  *
diff --git a/examples/developer-tools/src/view_model.ts b/examples/developer-tools/src/view_model.ts
index b8c84cfaab..a5114ae89c 100644
--- a/examples/developer-tools/src/view_model.ts
+++ b/examples/developer-tools/src/view_model.ts
@@ -6,6 +6,8 @@
 
 import '@material/web/menu/menu';
 import '@material/web/menu/menu-item';
+import '@material/web/dialog/dialog';
+import '@material/web/button/text-button';
 
 export class ViewModel {
   mainWorkspaceDiv = document.getElementById('main-workspace');
@@ -20,6 +22,13 @@ export class ViewModel {
   loadButton = document.getElementById('load-btn');
   loadMenu = document.getElementById('load-menu');
 
+  fileModal = document.getElementById('file-upload-modal');
+  fileModalCloseButton = document.getElementById('file-upload-close');
+  fileDropZone = document.getElementById('file-upload-drop-zone');
+  fileUploadInput = document.getElementById('file-upload');
+  fileLabel = document.getElementById('file-label');
+  fileUploadWarning = document.getElementById('file-upload-warning');
+
   /**
    * Gets a string representing the format of the block
    * definition the user selected.
@@ -92,4 +101,40 @@ export class ViewModel {
       ? (importButton.checked = true)
       : (scriptButton.checked = true);
   }
+
+  /**
+   * Shows or hides the file upload modal.
+   *
+   * @param show true to show, false to hide.
+   */
+  toggleFileUploadModal(show: boolean) {
+    if (show) {
+      this.fileModal.setAttribute('open', '');
+
+      // Set z-index of scrim so that it covers the Blockly toolbox
+      // https://github.com/material-components/material-web/issues/4948
+      if (this.fileModal.shadowRoot) {
+        const scrim =
+          this.fileModal.shadowRoot.querySelector<HTMLElement>('.scrim');
+        if (scrim) {
+          scrim.style.zIndex = '99';
+        }
+      }
+    } else {
+      this.fileModal.removeAttribute('open');
+    }
+  }
+
+  /**
+   * Shows or hides the file upload error message.
+   *
+   * @param show true to show, false to hide.
+   */
+  toggleFileUploadWarning(show: boolean) {
+    if (show) {
+      this.fileUploadWarning.style.visibility = 'visible';
+    } else {
+      this.fileUploadWarning.style.visibility = 'hidden';
+    }
+  }
 }