diff --git a/chainforge/react-server/package-lock.json b/chainforge/react-server/package-lock.json
index b0aca99..1e01d0e 100644
--- a/chainforge/react-server/package-lock.json
+++ b/chainforge/react-server/package-lock.json
@@ -45,6 +45,7 @@
         "emoji-mart": "^5.5.2",
         "emoji-picker-react": "^4.4.9",
         "google-auth-library": "^8.8.0",
+        "lz-string": "^1.5.0",
         "mantine-contextmenu": "^1.2.15",
         "mantine-react-table": "^1.0.0-beta.8",
         "openai": "^3.3.0",
diff --git a/chainforge/react-server/package.json b/chainforge/react-server/package.json
index 748d900..e16c3a8 100644
--- a/chainforge/react-server/package.json
+++ b/chainforge/react-server/package.json
@@ -40,6 +40,7 @@
     "emoji-mart": "^5.5.2",
     "emoji-picker-react": "^4.4.9",
     "google-auth-library": "^8.8.0",
+    "lz-string": "^1.5.0",
     "mantine-contextmenu": "^1.2.15",
     "mantine-react-table": "^1.0.0-beta.8",
     "openai": "^3.3.0",
diff --git a/chainforge/react-server/src/backend/__test__/backend.test.ts b/chainforge/react-server/src/backend/__test__/backend.test.ts
new file mode 100644
index 0000000..f56864f
--- /dev/null
+++ b/chainforge/react-server/src/backend/__test__/backend.test.ts
@@ -0,0 +1,28 @@
+/*
+* @jest-environment node
+*/
+import { LLM } from '../models';
+import { expect, test } from '@jest/globals';
+import { queryLLM } from '../backend';
+import { StandardizedLLMResponse } from '../typing';
+
+test('call three LLMs with a single prompt', async () => {
+  // Setup params to call
+  const prompt = 'What is one major difference between French and English languages? Be brief.'
+  const llms = [LLM.OpenAI_ChatGPT, LLM.Claude_v1, LLM.PaLM2_Chat_Bison];
+  const n = 1;
+  const progress_listener = (progress: {[key: symbol]: any}) => {
+    console.log(JSON.stringify(progress));
+  };
+
+  // Call all three LLMs with the same prompt, n=1, and listen to progress
+  const {responses, errors} = await queryLLM('testid', llms, n, prompt, {}, undefined, progress_listener);
+
+  // Check responses
+  expect(responses).toHaveLength(3);
+  responses.forEach((resp_obj: StandardizedLLMResponse) => {
+    expect(resp_obj.prompt).toBe(prompt);
+    expect(resp_obj.responses).toHaveLength(1); // since n = 1
+    expect(Object.keys(resp_obj.vars)).toHaveLength(0);
+  });
+}, 40000);
\ No newline at end of file
diff --git a/chainforge/react-server/src/backend/__test__/cache.test.ts b/chainforge/react-server/src/backend/__test__/cache.test.ts
new file mode 100644
index 0000000..bb43221
--- /dev/null
+++ b/chainforge/react-server/src/backend/__test__/cache.test.ts
@@ -0,0 +1,32 @@
+import { expect, test } from '@jest/globals';
+import StorageCache from '../cache';
+
+test('saving and loading cache data from localStorage', () => {
+  // Store Unicode and numeric data into StorageCache
+  StorageCache.store('hello', {'a': '土', 'b': 'ہوا', 'c': '火'});
+  StorageCache.store('world', 42);
+
+  // Verify stored data:
+  let d = StorageCache.get('hello');
+  expect(d).toHaveProperty('a');
+  expect(d?.a).toBe('土');
+  
+  // Save to localStorage
+  StorageCache.saveToLocalStorage('test');
+
+  // Remove all data in the cache
+  StorageCache.clear();
+
+  // Double-check there's no data:
+  d = StorageCache.get('hello');
+  expect(d).toBeUndefined();
+
+  // Load cache from localStorage
+  StorageCache.loadFromLocalStorage('test');
+
+  // Verify stored data:
+  d = StorageCache.get('hello');
+  expect(d).toHaveProperty('c');
+  expect(d?.c).toBe('火');
+  expect(StorageCache.get('world')).toBe(42);
+});
\ No newline at end of file
diff --git a/chainforge/react-server/src/backend/backend.ts b/chainforge/react-server/src/backend/backend.ts
index 2e8bf62..caebfaa 100644
--- a/chainforge/react-server/src/backend/backend.ts
+++ b/chainforge/react-server/src/backend/backend.ts
@@ -9,7 +9,7 @@
 // from chainforge.promptengine.template import PromptTemplate, PromptPermutationGenerator
 // from chainforge.promptengine.utils import LLM, is_valid_filepath, get_files_at_dir, create_dir_if_not_exists, set_api_keys
 
-import { Dict, LLMResponseError, LLMResponseObject } from "./typing";
+import { Dict, LLMResponseError, LLMResponseObject, StandardizedLLMResponse } from "./typing";
 import { LLM } from "./models";
 import { set_api_keys } from "./utils";
 import StorageCache from "./cache";
@@ -117,16 +117,6 @@ Object.entries(LLM).forEach(([key, value]) => {
 //         md_ast_parser = mistune.create_markdown(renderer='ast')
 //         return md_ast_parser(self.text)
 
-interface StandardizedLLMResponse {
-  llm: string | Dict,
-  prompt: string,
-  responses: Array<string>,
-  vars: Dict,
-  metavars: Dict,
-  tokens: Dict,
-  eval_res?: Dict,
-}
-
 function to_standard_format(r: LLMResponseObject | Dict): StandardizedLLMResponse {
   let resp_obj = {
     vars: r['info'],
@@ -555,6 +545,7 @@ export async function queryLLM(id: string,
                                prompt: string,
                                vars: Dict,
                                api_keys?: Dict,
+                               progress_listener?: (progress: {[key: symbol]: any}) => void,
                                no_cache?: boolean): Promise<Dict> {
   // Verify the integrity of the params
   if (typeof id !== 'string' || id.trim().length === 0)
@@ -582,7 +573,8 @@ export async function queryLLM(id: string,
   
   // Get the storage keys of any cache files for specific models + settings
   const llms = llm;
-  let cache = StorageCache.get(id);  // returns {} if 'id' is not in the storage cache yet
+  let cache: Dict = StorageCache.get(id) || {};  // returns {} if 'id' is not in the storage cache yet
+
   let llm_to_cache_filename = {};
   let past_cache_files = {};
   if (typeof cache === 'object' && cache.cache_files !== undefined) {
@@ -608,7 +600,7 @@ export async function queryLLM(id: string,
     // Create a new cache JSON object
     cache = { cache_files: {}, responses_last_run: [] };
     let prev_filenames: Array<string> = [];
-    llms.forEach(llm_spec => {
+    llms.forEach((llm_spec: string | Dict) => {
       const fname = gen_unique_cache_filename(id, prev_filenames);
       llm_to_cache_filename[extract_llm_key(llm_spec)] = fname;
       cache.cache_files[fname] = llm_spec;
@@ -625,10 +617,13 @@ export async function queryLLM(id: string,
   let progressProxy = new Proxy(progress, {
     set: function (target, key, value) {
       console.log(`${key.toString()} set to ${value.toString()}`);
-      // ...
-      // Call any callbacks here
-      // ...
       target[key] = value;
+
+      // If the caller provided a callback, notify it 
+      // of the changes to the 'progress' object:
+      if (progress_listener)
+        progress_listener(target);
+
       return true;
     }
   });
diff --git a/chainforge/react-server/src/backend/cache.ts b/chainforge/react-server/src/backend/cache.ts
index 34eadf0..810bb39 100644
--- a/chainforge/react-server/src/backend/cache.ts
+++ b/chainforge/react-server/src/backend/cache.ts
@@ -1,4 +1,5 @@
 import { Dict } from "./typing";
+import LZString from 'lz-string';
 
 /**
  * Singleton JSON cache that functions like a local filesystem in a Python backend, 
@@ -21,10 +22,10 @@ export default class StorageCache {
     return StorageCache.instance;
   }
 
-  private getCacheData(key: string): Dict {
-    return this.data[key] || {};
+  private getCacheData(key: string): Dict | undefined {
+    return this.data[key] || undefined;
   }
-  public static get(key: string): Dict {
+  public static get(key: string): Dict | undefined {
     return StorageCache.getInstance().getCacheData(key);
   }
   
@@ -34,4 +35,62 @@ export default class StorageCache {
   public static store(key: string, data: any): void {
     StorageCache.getInstance().storeCacheData(key, data);
   }
+
+  private clearCache(): void {
+    this.data = {};
+  }
+  public static clear(): void {
+    StorageCache.getInstance().clearCache();
+  }
+
+  /**
+   * Attempts to store the entire cache in localStorage. 
+   * Performs lz-string compression (https://pieroxy.net/blog/pages/lz-string/index.html)
+   * before storing a JSON object in UTF encoding.
+   * 
+   * Use loadFromLocalStorage to unpack the localStorage data.
+   * 
+   * @param localStorageKey The key that will be used in localStorage (default='chainforge')
+   * @returns True if succeeded, false if failure (e.g., too big for localStorage).
+   */
+  public static saveToLocalStorage(localStorageKey: string='chainforge'): boolean {
+    const data = StorageCache.getInstance().data;
+    const compressed = LZString.compressToUTF16(JSON.stringify(data));
+    try {
+      localStorage.setItem(localStorageKey, compressed);
+      return true;
+    } catch (error) {
+      if (error instanceof DOMException && error.name === "QuotaExceededError") {
+        // Handle the error when storage quota is exceeded
+        console.warn("Storage quota exceeded");
+      } else {
+        // Handle other types of storage-related errors
+        console.error("Error storing data in localStorage:", error.message);
+      }
+      return false;
+    }
+  }
+
+  /**
+   * Attempts to load a previously stored cache JSON from localStorage.
+   * Performs lz-string decompression from UTF16 encoding. 
+   * 
+   * @param localStorageKey The key that will be used in localStorage (default='chainforge')
+   * @returns True if succeeded, false if failure (e.g., key not found). 
+   */
+  public static loadFromLocalStorage(localStorageKey: string='chainforge'): boolean {
+    const compressed = localStorage.getItem(localStorageKey);
+    if (!compressed) {
+      console.error(`Could not find cache data in localStorage with key ${localStorageKey}.`);
+      return false;
+    }
+    try {
+      let data = JSON.parse(LZString.decompressFromUTF16(compressed));
+      StorageCache.getInstance().data = data;
+      return true;
+    } catch (error) {
+      console.error(error.message);
+      return false;
+    }
+  }
 }
\ No newline at end of file
diff --git a/chainforge/react-server/src/backend/query.ts b/chainforge/react-server/src/backend/query.ts
index 97dce22..4a27eb0 100644
--- a/chainforge/react-server/src/backend/query.ts
+++ b/chainforge/react-server/src/backend/query.ts
@@ -214,7 +214,7 @@ export class PromptPipeline {
    * Useful for continuing if computation was interrupted halfway through. 
    */
   _load_cached_responses(): {[key: string]: LLMResponseObject} {
-    return StorageCache.get(this._storageKey);
+    return StorageCache.get(this._storageKey) || {};
   }
 
   /**
diff --git a/chainforge/react-server/src/backend/typing.ts b/chainforge/react-server/src/backend/typing.ts
index 3b78201..7a03016 100644
--- a/chainforge/react-server/src/backend/typing.ts
+++ b/chainforge/react-server/src/backend/typing.ts
@@ -29,4 +29,15 @@ export interface LLMAPICall {
    n: number,
    temperature: number,
    params?: Dict): Promise<[Dict, Dict]>
+}
+
+/** A standard response format expected by the front-end. */
+export interface StandardizedLLMResponse {
+  llm: string | Dict,
+  prompt: string,
+  responses: Array<string>,
+  vars: Dict,
+  metavars: Dict,
+  tokens: Dict,
+  eval_res?: Dict,
 }
\ No newline at end of file