Merge remote-tracking branch 'origin/main' into lee/add-workflow-editor

* feat: support dev mode for backend ts server

* update message

* validate typescript file

* fix: format

* use temp file to avoid server restart

* fix format

* use npx tsc

* remove typescript deps

.changeset/olive-mangos-fly.md

@@ -0,0 +1,5 @@
+---
+"@llamaindex/server": patch
+---
+
+feat: add dev mode UI

packages/server/examples/devmode/README.md

@@ -0,0 +1,21 @@
+This example shows how to use the dev mode of the server.
+
+First, we need to set `devMode` to `true` in the `uiConfig` of the server.
+
+```ts
+new LlamaIndexServer({
+  workflow: workflowFactory,
+  uiConfig: {
+    appTitle: "Calculator",
+    devMode: true,
+  },
+  port: 6000,
+}).start();
+```
+
+Export OpenAI API key and start the server in dev mode.
+
+```bash
+export OPENAI_API_KEY=<your-openai-api-key>
+npx tsx watch index.ts
+```

packages/server/examples/devmode/index.ts

@@ -0,0 +1,15 @@
+import { LlamaIndexServer } from "@llamaindex/server";
+import { workflowFactory } from "./src/app/workflow";
+
+new LlamaIndexServer({
+  workflow: workflowFactory,
+  uiConfig: {
+    appTitle: "Calculator",
+    devMode: true,
+    starterQuestions: [
+      "What is the weather in Tokyo?",
+      "What is the weather in New York?",
+    ],
+  },
+  port: 6005,
+}).start();

packages/server/examples/devmode/src/app/workflow.ts

@@ -0,0 +1,16 @@
+import { agent } from "@llamaindex/workflow";
+import { tool } from "llamaindex";
+import { z } from "zod";
+
+export const workflowFactory = async () => {
+  return agent({
+    tools: [
+      tool({
+        name: "weather",
+        description: "Get the weather in a specific city",
+        parameters: z.object({ city: z.string() }),
+        execute: ({ city }) => `The weather in ${city} is sunny`,
+      }),
+    ],
+  });
+};

packages/server/next/app/components/ui/chat/chat-section.tsx

@@ -13,6 +13,7 @@ import CustomChatMessages from "./chat-messages";
 import { DynamicEventsErrors } from "./custom/events/dynamic-events-errors";
 import { fetchComponentDefinitions } from "./custom/events/loader";
 import { ComponentDef } from "./custom/events/types";
+import { DevModePanel } from "./dev-mode-panel";
 
 export default function ChatSection() {
   const handler = useChat({
@@ -35,12 +36,13 @@ export default function ChatSection() {
         <ChatHeader />
         <ChatUI
           handler={handler}
-          className="flex min-h-0 flex-1 flex-row justify-center gap-4 px-4 py-0"
+          className="relative flex min-h-0 flex-1 flex-row justify-center gap-4 px-4 py-0"
         >
           <ResizablePanelGroup direction="horizontal">
             <ChatSectionPanel />
             <ChatCanvasPanel />
           </ResizablePanelGroup>
+          <DevModePanel />
         </ChatUI>
       </div>
       <ChatInjection />

packages/server/next/app/components/ui/chat/dev-mode-panel.tsx

@@ -0,0 +1,270 @@
+"use client";
+
+import {
+  CodeEditor,
+  fileExtensionToEditorLang,
+} from "@llamaindex/chat-ui/widgets";
+import { AlertCircle, Loader2 } from "lucide-react";
+import { useEffect, useState } from "react";
+import { Button } from "../button";
+import { getConfig } from "../lib/utils";
+
+const API_PATH = "/api/dev/files/workflow";
+const POLLING_TIMEOUT = 30_000; // 30 seconds
+
+type WorkflowFile = {
+  last_modified: number;
+  file_path: string;
+  content: string;
+};
+
+export function DevModePanel() {
+  const devModeEnabled = getConfig("DEV_MODE");
+  if (!devModeEnabled) return null;
+  return <DevModePanelComp />;
+}
+
+function DevModePanelComp() {
+  const [devModeOpen, setDevModeOpen] = useState(false);
+
+  const [isFetching, setIsFetching] = useState(false);
+  const [fetchingError, setFetchingError] = useState<string | null>();
+  const [workflowFile, setWorkflowFile] = useState<WorkflowFile | null>(null);
+
+  const [updatedCode, setUpdatedCode] = useState<string | null>(null);
+  const [isSaving, setIsSaving] = useState(false);
+  const [saveError, setSaveError] = useState<string | null>(null);
+
+  const [isPolling, setIsPolling] = useState(false);
+  const [pollingError, setPollingError] = useState<string | null>(null);
+
+  async function fetchWorkflowCode() {
+    try {
+      setIsFetching(true);
+      const response = await fetch(API_PATH);
+      const data = await response.json();
+
+      if (!response.ok) {
+        throw new Error(data?.detail ?? "Unknown error");
+      }
+
+      setWorkflowFile(data);
+      setFetchingError(null);
+    } catch (error) {
+      const errorMessage =
+        error instanceof Error ? error.message : "Unknown error";
+      setFetchingError(errorMessage);
+      console.warn("Error fetching workflow code:", error);
+    } finally {
+      setIsFetching(false);
+    }
+  }
+
+  async function restartingWorkflow() {
+    if (!workflowFile) return;
+
+    const initialLastModified = workflowFile.last_modified;
+    setIsPolling(true);
+    setPollingError(null);
+
+    const pollStartTime = Date.now();
+
+    // interval refetching the updated workflow code
+    const poll = async () => {
+      if (Date.now() - pollStartTime > POLLING_TIMEOUT) {
+        setPollingError(
+          `Server not responding after ${POLLING_TIMEOUT / 1000} seconds.`,
+        );
+        return;
+      }
+
+      try {
+        const pollResponse = await fetch(API_PATH);
+        const pollData = (await pollResponse.json()) as WorkflowFile;
+        if (pollData.last_modified !== initialLastModified) {
+          setWorkflowFile(pollData);
+          setUpdatedCode(pollData.content);
+          setIsPolling(false);
+          setPollingError(null);
+          setDevModeOpen(false);
+        } else {
+          setTimeout(poll, 2000);
+        }
+      } catch (error) {
+        console.info("Polling error", error);
+        setTimeout(poll, 2000);
+      }
+    };
+
+    setTimeout(poll, 2000);
+  }
+
+  const handleResetCode = () => {
+    setUpdatedCode(workflowFile?.content ?? null);
+    setSaveError(null);
+  };
+
+  const handleSaveCode = async () => {
+    if (!workflowFile) return;
+
+    try {
+      setIsSaving(true);
+      const response = await fetch(API_PATH, {
+        method: "PUT",
+        headers: {
+          Accept: "application/json",
+          "Content-Type": "application/json",
+        },
+        body: JSON.stringify({
+          content: updatedCode,
+          file_path: workflowFile.file_path,
+        }),
+      });
+      const data = await response.json();
+      if (!response.ok) {
+        throw new Error(data?.detail ?? "Unknown error");
+      }
+      setSaveError(null);
+      await restartingWorkflow();
+    } catch (error) {
+      console.warn("Error saving workflow code:", error);
+      setSaveError(
+        error instanceof Error
+          ? error.message
+          : "Unknown error happened when saving workflow code",
+      );
+    } finally {
+      setIsSaving(false);
+    }
+  };
+
+  useEffect(() => {
+    if (devModeOpen) {
+      fetchWorkflowCode();
+    }
+  }, [devModeOpen]);
+
+  const codeEditorLanguage = fileExtensionToEditorLang(
+    workflowFile?.file_path.split(".").pop() ?? "",
+  );
+
+  return (
+    <>
+      <Button
+        onClick={() => setDevModeOpen(!devModeOpen)}
+        className="fixed right-2 top-1/2 origin-right -translate-y-1/2 rotate-90 transform rounded-l-md shadow-md transition-transform hover:-translate-x-1"
+      >
+        Dev Mode
+      </Button>
+
+      {isPolling && (
+        <div className="fixed inset-0 z-50 flex flex-col items-center justify-center bg-black/50 backdrop-blur-sm">
+          {!pollingError && (
+            <>
+              <Loader2 className="mb-4 h-16 w-16 animate-spin text-white" />
+              <p className="text-lg font-semibold text-white">
+                Applying changes and restarting server...
+              </p>
+              <p className="mt-2 text-sm text-slate-300">
+                Please wait for a while then you can start chatting with the
+                updated workflow.
+              </p>
+            </>
+          )}
+          {pollingError && (
+            <div className="bg-destructive/20 text-destructive-foreground mt-4 max-w-md rounded-md p-4 text-center">
+              <div className="mb-2 flex items-center justify-center gap-2">
+                <AlertCircle className="shrink-0" size={16} />
+                <h6 className="text-sm font-medium">Server Starting Error</h6>
+              </div>
+              <p className="text-sm">{pollingError}</p>
+
+              <p className="text-sm">
+                Please reload the page and check server logs.
+              </p>
+            </div>
+          )}
+        </div>
+      )}
+
+      <div
+        className={`border-border fixed right-0 top-0 z-10 h-full w-full border-l shadow-xl transition-all duration-300 ease-in-out ${
+          devModeOpen ? "translate-x-0 bg-black/50" : "translate-x-full"
+        }`}
+        onClick={() => setDevModeOpen(false)}
+      >
+        <div
+          className={`bg-background ml-auto flex h-full w-[800px] flex-col p-4`}
+          onClick={(e) => e.stopPropagation()}
+        >
+          <div className="mb-4 flex items-center justify-between">
+            <div>
+              <h2 className="text-xl font-bold">Workflow Editor</h2>
+              <p className="text-muted-foreground text-sm">
+                {isFetching ? (
+                  "Loading..."
+                ) : workflowFile ? (
+                  <>
+                    Edit the code of <b>{workflowFile.file_path}</b> and save to
+                    apply changes to your workflow.
+                  </>
+                ) : (
+                  ""
+                )}
+              </p>
+            </div>
+            <Button
+              variant="outline"
+              size="sm"
+              onClick={() => setDevModeOpen(false)}
+            >
+              Close
+            </Button>
+          </div>
+          <div className="flex-1 overflow-auto">
+            {fetchingError ? (
+              <div className="bg-destructive/10 text-destructive/70 mb-4 flex items-center gap-2 rounded-md p-4">
+                <AlertCircle className="shrink-0" size={16} />
+                <p className="text-sm font-medium">{fetchingError}</p>
+              </div>
+            ) : (
+              <CodeEditor
+                code={updatedCode ?? workflowFile?.content ?? ""}
+                onChange={setUpdatedCode}
+                language={codeEditorLanguage}
+              />
+            )}
+          </div>
+          <div className="mt-4 flex flex-col">
+            {saveError && (
+              <div className="bg-destructive/10 text-destructive/70 mb-4 rounded-md p-4">
+                <div className="mb-2 flex items-center gap-2">
+                  <AlertCircle className="shrink-0" size={16} />
+                  <h6 className="text-sm font-medium">Error Saving Code</h6>
+                </div>
+                <p className="whitespace-pre-wrap text-sm">{saveError}</p>
+              </div>
+            )}
+
+            <div className="flex justify-end gap-2">
+              <Button
+                variant="outline"
+                className="mr-2"
+                onClick={handleResetCode}
+              >
+                Reset Code
+              </Button>
+              <Button
+                onClick={handleSaveCode}
+                disabled={isSaving || !updatedCode || !workflowFile}
+              >
+                Save & Restart Server
+                {isSaving && <Loader2 className="ml-2 h-4 w-4 animate-spin" />}
+              </Button>
+            </div>
+          </div>
+        </div>
+      </div>
+    </>
+  );
+}

packages/server/package.json

@@ -55,7 +55,7 @@
     "@babel/traverse": "^7.27.0",
     "@babel/types": "^7.27.0",
     "@hookform/resolvers": "^5.0.1",
-    "@llamaindex/chat-ui": "0.4.3",
+    "@llamaindex/chat-ui": "0.4.4",
     "@radix-ui/react-accordion": "^1.2.3",
     "@radix-ui/react-alert-dialog": "^1.1.7",
     "@radix-ui/react-aspect-ratio": "^1.1.3",

packages/server/src/handlers/files.ts

@@ -1,7 +1,9 @@
+import { exec } from "child_process";
 import fs from "fs";
 import type { IncomingMessage, ServerResponse } from "http";
+import path from "path";
 import { promisify } from "util";
-import { sendJSONResponse } from "../utils/request";
+import { parseRequestBody, sendJSONResponse } from "../utils/request";
 
 export const handleServeFiles = async (
   req: IncomingMessage,
@@ -21,3 +23,84 @@ export const handleServeFiles = async (
     return sendJSONResponse(res, 404, { error: "File not found" });
   }
 };
+
+const DEFAULT_WORKFLOW_FILE_PATH = "src/app/workflow.ts"; // TODO: we can make it as a parameter in server later
+
+export const getWorkflowFile = async (
+  req: IncomingMessage,
+  res: ServerResponse,
+  filePath: string = DEFAULT_WORKFLOW_FILE_PATH,
+) => {
+  const fileExists = await promisify(fs.exists)(filePath);
+  if (!fileExists) {
+    return sendJSONResponse(res, 404, {
+      detail: `Dev mode is currently in beta. It only supports updating workflow file at ${DEFAULT_WORKFLOW_FILE_PATH}`,
+    });
+  }
+
+  const content = await promisify(fs.readFile)(filePath, "utf-8");
+  const last_modified = fs.statSync(filePath).mtime.getTime();
+  sendJSONResponse(res, 200, { content, file_path: filePath, last_modified });
+};
+
+export const updateWorkflowFile = async (
+  req: IncomingMessage,
+  res: ServerResponse,
+  filePath: string = DEFAULT_WORKFLOW_FILE_PATH,
+) => {
+  const body = await parseRequestBody(req);
+  const { content } = body as { content: string };
+
+  const fileExists = await promisify(fs.exists)(filePath);
+  if (!fileExists) {
+    return sendJSONResponse(res, 404, {
+      detail: `Dev mode is currently in beta. It only supports updating workflow file at ${DEFAULT_WORKFLOW_FILE_PATH}`,
+    });
+  }
+
+  try {
+    const resolvedFilePath = path.resolve(DEFAULT_WORKFLOW_FILE_PATH);
+    const result = await validateTypeScriptFile(resolvedFilePath, content);
+
+    if (!result.isValid) {
+      return sendJSONResponse(res, 400, {
+        detail: result.errors.join("\n"),
+      });
+    }
+
+    await promisify(fs.writeFile)(filePath, content);
+    sendJSONResponse(res, 200, { content });
+  } catch (error) {
+    console.error("Error updating workflow file:", error);
+    sendJSONResponse(res, 500, { error: "Failed to update workflow file" });
+  }
+};
+
+// use typescript package to validate the file syntax and imports
+async function validateTypeScriptFile(filePath: string, content: string) {
+  // Update workflow file directly will cause the server restart immediately.
+  // So we create a temporary file with the same content in the same directory as the workflow file
+  // This file will be used to validate the file syntax and imports. It will be deleted after validation.
+  const tempFilePath = path.join(
+    path.dirname(filePath),
+    `workflow_${Date.now()}.ts`,
+  );
+  fs.writeFileSync(tempFilePath, content);
+
+  const errors = [];
+  try {
+    const tscCommand = `npx tsc ${tempFilePath} --noEmit --skipLibCheck true`;
+    await promisify(exec)(tscCommand);
+  } catch (error) {
+    const errorMessage = (error as { stdout: string })?.stdout;
+    errors.push(errorMessage);
+  } finally {
+    // Clean up temporary file
+    if (fs.existsSync(tempFilePath)) fs.unlinkSync(tempFilePath);
+  }
+
+  return {
+    isValid: errors.length === 0,
+    errors: errors,
+  };
+}

packages/server/src/server.ts

@@ -9,8 +9,13 @@ import { promisify } from "util";
 import { handleChat } from "./handlers/chat";
 import { getLlamaCloudConfig } from "./handlers/cloud";
 import { getComponents } from "./handlers/components";
-import { handleServeFiles } from "./handlers/files";
+import {
+  getWorkflowFile,
+  handleServeFiles,
+  updateWorkflowFile,
+} from "./handlers/files";
 import type { LlamaIndexServerOptions } from "./types";
+
 const nextDir = path.join(__dirname, "..", "server");
 const configFile = path.join(__dirname, "..", "server", "public", "config.js");
 const dev = process.env.NODE_ENV !== "production";
@@ -44,6 +49,7 @@ export class LlamaIndexServer {
         ? "/api/chat/config/llamacloud"
         : undefined;
     const componentsApi = this.componentsDir ? "/api/components" : undefined;
+    const devMode = uiConfig?.devMode ?? false;
 
     // content in javascript format
     const content = `
@@ -52,7 +58,8 @@ export class LlamaIndexServer {
         APP_TITLE: ${JSON.stringify(appTitle)},
         LLAMA_CLOUD_API: ${JSON.stringify(llamaCloudApi)},
         STARTER_QUESTIONS: ${JSON.stringify(starterQuestions)},
-        COMPONENTS_API: ${JSON.stringify(componentsApi)}
+        COMPONENTS_API: ${JSON.stringify(componentsApi)},
+        DEV_MODE: ${JSON.stringify(devMode)}
       }
     `;
     fs.writeFileSync(configFile, content);
@@ -96,6 +103,14 @@ export class LlamaIndexServer {
         return getLlamaCloudConfig(req, res);
       }
 
+      if (pathname === "/api/dev/files/workflow" && req.method === "GET") {
+        return getWorkflowFile(req, res);
+      }
+
+      if (pathname === "/api/dev/files/workflow" && req.method === "PUT") {
+        return updateWorkflowFile(req, res);
+      }
+
       const handle = this.app.getRequestHandler();
       handle(req, res, parsedUrl);
     });

packages/server/src/types.ts

@@ -17,6 +17,7 @@ export type UIConfig = {
   starterQuestions?: string[];
   componentsDir?: string;
   llamaCloudIndexSelector?: boolean;
+  devMode?: boolean;
 };
 
 export type LlamaIndexServerOptions = NextAppOptions & {

pnpm-lock.yaml

@@ -181,8 +181,8 @@ importers:
         specifier: ^5.0.1
         version: 5.0.1(react-hook-form@7.56.1(react@19.1.0))
       '@llamaindex/chat-ui':
-        specifier: 0.4.3
+        specifier: 0.4.4
-        version: 0.4.3(@babel/runtime@7.27.0)(@codemirror/autocomplete@6.18.6)(@codemirror/language@6.11.0)(@codemirror/lint@6.8.5)(@codemirror/search@6.5.10)(@codemirror/state@6.5.2)(@codemirror/theme-one-dark@6.1.2)(@codemirror/view@6.36.7)(@types/react-dom@19.1.2(@types/react@19.1.2))(@types/react@19.1.2)(codemirror@6.0.1)(react-dom@19.1.0(react@19.1.0))(react@19.1.0)
+        version: 0.4.4(@babel/runtime@7.27.0)(@codemirror/autocomplete@6.18.6)(@codemirror/language@6.11.0)(@codemirror/lint@6.8.5)(@codemirror/search@6.5.10)(@codemirror/state@6.5.2)(@codemirror/theme-one-dark@6.1.2)(@codemirror/view@6.36.7)(@types/react-dom@19.1.2(@types/react@19.1.2))(@types/react@19.1.2)(codemirror@6.0.1)(react-dom@19.1.0(react@19.1.0))(react@19.1.0)
       '@llamaindex/env':
         specifier: ^0.1.29
         version: 0.1.29
@@ -1177,8 +1177,8 @@ packages:
       zod:
         optional: true
 
-  '@llamaindex/chat-ui@0.4.3':
+  '@llamaindex/chat-ui@0.4.4':
-    resolution: {integrity: sha512-JeS5pzEXZRRzTL70lHRtbWbaPjeZuMMHlqkTNBgYqc2eMM+o9VMOzVKKsXoYfOeE+wunqJd+cBrtkECGEmhRZg==}
+    resolution: {integrity: sha512-sE3mJxlmAV3eiIaqOnioUNYYBLJJL8sy2mdFP4xXDf3PfkcEn0wT2Om/ButpVgIXHlPG9lONtv8mzw7hWq2Atg==}
     peerDependencies:
       react: ^18.2.0 || ^19.0.0 || ^19.0.0-rc
 
@@ -7113,7 +7113,7 @@ snapshots:
       next: 15.3.1(@opentelemetry/api@1.9.0)(@playwright/test@1.52.0)(react-dom@19.1.0(react@19.1.0))(react@19.1.0)
       zod: 3.24.3
 
-  '@llamaindex/chat-ui@0.4.3(@babel/runtime@7.27.0)(@codemirror/autocomplete@6.18.6)(@codemirror/language@6.11.0)(@codemirror/lint@6.8.5)(@codemirror/search@6.5.10)(@codemirror/state@6.5.2)(@codemirror/theme-one-dark@6.1.2)(@codemirror/view@6.36.7)(@types/react-dom@19.1.2(@types/react@19.1.2))(@types/react@19.1.2)(codemirror@6.0.1)(react-dom@19.1.0(react@19.1.0))(react@19.1.0)':
+  '@llamaindex/chat-ui@0.4.4(@babel/runtime@7.27.0)(@codemirror/autocomplete@6.18.6)(@codemirror/language@6.11.0)(@codemirror/lint@6.8.5)(@codemirror/search@6.5.10)(@codemirror/state@6.5.2)(@codemirror/theme-one-dark@6.1.2)(@codemirror/view@6.36.7)(@types/react-dom@19.1.2(@types/react@19.1.2))(@types/react@19.1.2)(codemirror@6.0.1)(react-dom@19.1.0(react@19.1.0))(react@19.1.0)':
     dependencies:
       '@codemirror/lang-css': 6.3.1
       '@codemirror/lang-html': 6.4.9

python/llama-index-server/README.md

@@ -83,6 +83,7 @@ The LlamaIndexServer accepts the following configuration parameters:
   - `ui_path`: Path for downloaded UI static files (default: ".ui")
   - `component_dir`: The directory for custom UI components rendering events emitted by the workflow. The default is None, which does not render custom UI components.
   - `llamacloud_index_selector`: Whether to show the LlamaCloud index selector in the chat UI (default: False). Requires `LLAMA_CLOUD_API_KEY` to be set.
+  - `dev_mode`: When enabled, you can update workflow code in the UI and see the changes immediately. It's currently in beta and only supports updating workflow code at `app/workflow.py`. You might also need to set `env="dev"` and start the server with the reload feature enabled.
 - `verbose`: Enable verbose logging
 - `api_prefix`: API route prefix (default: "/api")
 - `server_url`: The deployment URL of the server (default is None)
@@ -120,6 +121,21 @@ In development mode (`env="dev"`), the server:
 - Automatically includes the chat UI
 - Provides more verbose logging
 
+### Workflow Editor (Beta)
+
+In development mode, you can set `dev_mode` to `True` in the UI configuration to enable the workflow editor, which allows you to edit the workflow code directly in the browser.
+
+```python
+app = LlamaIndexServer(
+    workflow_factory=create_workflow,
+    env="dev",
+    ui_config={"dev_mode": True},
+)
+```
+
+**Note**: The workflow editor is currently in beta and only supports updating LlamaIndexServer projects created with [create-llama](https://github.com/run-llama/create-llama/). You also need to start the server via `fastapi dev` so that the server can hot reload the workflow code.
+
+
 ## API Endpoints
 
 The server provides the following default endpoints:

python/llama-index-server/examples/simple-agent/README.md

@@ -0,0 +1,38 @@
+# A simple chat app
+
+This guide explains how to set up and use the LlamaIndex server with a simple chatbot agent.
+
+## Prerequisites
+
+- [uv](https://github.com/astral-sh/uv) installed (a fast Python package manager and runner)
+- An OpenAI API key
+
+## Steps
+
+1. **Set the OpenAI API Key**
+
+   Export your OpenAI API key as an environment variable:
+
+   ```sh
+   export OPENAI_API_KEY=your_openai_api_key_here
+   ```
+
+2. **Run the Server Using uv**
+
+   Start the server with the following command:
+
+   ```sh
+   uv run workflow.py
+   ```
+
+   This will launch the FastAPI server using the workflow defined in `main.py`.
+
+3. **Access the Application**
+
+   Open your browser and go to:
+
+   ```
+   http://localhost:8000
+   ```
+
+   You will see the LlamaIndex chat app UI, where you can interact with the agent.

python/llama-index-server/examples/simple-agent/app/workflow.py

@@ -0,0 +1,14 @@
+from typing import Optional
+
+from llama_index.core.agent.workflow import AgentWorkflow
+from llama_index.core.settings import Settings
+from llama_index.llms.openai import OpenAI
+from llama_index.server.api.models import ChatRequest
+
+
+def create_workflow(chat_request: Optional[ChatRequest] = None) -> AgentWorkflow:
+    return AgentWorkflow.from_tools_or_functions(
+        tools_or_functions=[],
+        llm=Settings.llm or OpenAI(model="gpt-4o-mini"),
+        system_prompt="You are a helpful assistant that can tell a joke about Llama.",
+    )

python/llama-index-server/examples/simple-agent/main.py

@@ -0,0 +1,29 @@
+from app.workflow import create_workflow
+from fastapi import FastAPI
+
+from llama_index.server import LlamaIndexServer, UIConfig
+
+
+def create_app() -> FastAPI:
+    app = LlamaIndexServer(
+        workflow_factory=create_workflow,
+        ui_config=UIConfig(
+            app_title="Artifact",
+            starter_questions=[
+                "Tell me a funny joke.",
+                "Tell me some jokes about AI.",
+            ],
+            component_dir="components",
+            dev_mode=True,  # To show the dev UI, should disable this in production
+        ),
+    )
+    return app
+
+
+app = create_app()
+
+
+if __name__ == "__main__":
+    import uvicorn
+
+    uvicorn.run("main:app", host="0.0.0.0", port=8000, reload=True)

python/llama-index-server/llama_index/server/api/routers/__init__.py

@@ -1,4 +1,9 @@
 from llama_index.server.api.routers.chat import chat_router
 from llama_index.server.api.routers.ui import custom_components_router
+from llama_index.server.api.routers.dev import dev_router
 
-__all__ = ["chat_router", "custom_components_router"]
+__all__ = [
+    "chat_router",
+    "custom_components_router",
+    "dev_router",
+]

python/llama-index-server/llama_index/server/api/routers/dev.py

@@ -0,0 +1,102 @@
+import os
+import tempfile
+
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel, Field
+
+from llama_index.server.settings import server_settings
+from llama_index.server.utils.workflow_validation import validate_workflow_file
+
+
+class WorkflowFile(BaseModel):
+    last_modified: int
+    file_path: str = Field(
+        default="app/workflow.py",
+        description="Relative path to the workflow file",
+    )
+    content: str
+
+
+class WorkflowFileUpdate(BaseModel):
+    content: str
+    file_path: str = Field(
+        default="app/workflow.py",
+        description="Relative path to the workflow file",
+    )
+
+
+class WorkflowValidationResult(BaseModel):
+    valid: bool
+    error: str
+
+
+def dev_router() -> APIRouter:
+    # Use a prefix here to avoid conflicts with other routers
+    # but we probably don't need to do this
+    router = APIRouter(prefix="/dev", tags=["dev"])
+
+    default_workflow_file_path = "app/workflow.py"
+
+    @router.get("/files/workflow")
+    async def get_workflow_file() -> WorkflowFile:
+        """
+        Fetch the current workflow code
+        """
+        # Check if the file exists
+        if not os.path.exists(default_workflow_file_path):
+            raise HTTPException(
+                status_code=400,
+                detail="Dev mode is currently in beta. It only supports updating workflow file at 'app/workflow.py'",
+            )
+        stat = os.stat(default_workflow_file_path)
+        with open(default_workflow_file_path, "r") as f:
+            return WorkflowFile(
+                last_modified=int(stat.st_mtime),
+                file_path=default_workflow_file_path,
+                content=f.read(),
+            )
+
+    @router.post("/files/workflow/validate")
+    async def validate_workflow(file: WorkflowFileUpdate) -> WorkflowValidationResult:
+        """
+        Validate the current workflow code
+        """
+        try:
+            if file.file_path != default_workflow_file_path:
+                raise HTTPException(
+                    status_code=400, detail=f"Updating {file.file_path} is not allowed"
+                )
+            validate_workflow_file(
+                workflow_content=file.content,
+                factory_signature=server_settings.workflow_factory_signature,
+            )
+            return WorkflowValidationResult(valid=True, error="")
+        except Exception as e:
+            raise HTTPException(status_code=400, detail=str(e))
+
+    @router.put("/files/workflow")
+    async def put_workflow_file(update: WorkflowFileUpdate) -> None:
+        """
+        Update the current workflow code
+        """
+        # Validations
+        if update.file_path != default_workflow_file_path:
+            raise HTTPException(
+                status_code=400, detail=f"Updating {update.file_path} is not allowed"
+            )
+        with tempfile.NamedTemporaryFile("w", suffix=".py", delete=False) as tmp:
+            tmp.write(update.content)
+            tmp_path = tmp.name
+        try:
+            # Validate workflow file using the actual callable name from the workflow_factory
+            factory_func_name = server_settings.workflow_factory_signature
+            validate_workflow_file(
+                workflow_path=tmp_path, factory_signature=factory_func_name
+            )
+        except Exception as e:
+            raise HTTPException(status_code=400, detail=str(e))
+        # If all checks pass, overwrite the real file
+        with open(default_workflow_file_path, "w") as f:
+            f.write(update.content)
+
+    return router

python/llama-index-server/llama_index/server/server.py

@@ -10,7 +10,11 @@ from fastapi.staticfiles import StaticFiles
 from pydantic import BaseModel, Field
 
 from llama_index.core.workflow import Workflow
-from llama_index.server.api.routers import chat_router, custom_components_router
+from llama_index.server.api.routers import (
+    chat_router,
+    custom_components_router,
+    dev_router,
+)
 from llama_index.server.chat_ui import download_chat_ui
 from llama_index.server.settings import server_settings
 
@@ -33,6 +37,9 @@ class UIConfig(BaseModel):
     component_dir: Optional[str] = Field(
         default=None, description="The directory to custom UI components code"
     )
+    dev_mode: bool = Field(
+        default=False, description="Whether to enable the UI dev mode"
+    )
 
     def get_config_content(self) -> str:
         return json.dumps(
@@ -46,6 +53,7 @@ class UIConfig(BaseModel):
                 "COMPONENTS_API": f"{server_settings.api_url}/components"
                 if self.component_dir
                 else None,
+                "DEV_MODE": self.dev_mode,
             },
             indent=2,
         )
@@ -100,24 +108,33 @@ class LlamaIndexServer(FastAPI):
             server_settings.set_url(server_url)
         if api_prefix:
             server_settings.set_api_prefix(api_prefix)
-
+        server_settings.set_workflow_factory(workflow_factory.__name__)
-        if self.use_default_routers:
-            self.add_default_routers()
 
         if str(env).lower() == "dev":
             self.allow_cors("*")
             if self.ui_config.enabled is None:
                 self.ui_config.enabled = True
-
+        else:
+            if self.ui_config.enabled and self.ui_config.dev_mode:
+                raise ValueError(
+                    "UI dev mode requires the environment variable for LlamaIndexServer to be set to 'dev' and start the FastAPI app in dev mode."
+                )
         if self.ui_config.enabled is None:
             self.ui_config.enabled = False
 
+        # Routers
+        if self.use_default_routers:
+            self.add_default_routers()
+
+        # Should mount ui at the end
         if self.ui_config.enabled:
             self.mount_ui()
 
     # Default routers
     def add_default_routers(self) -> None:
         self.add_chat_router()
+        if self.ui_config.enabled and self.ui_config.dev_mode:
+            self.include_router(dev_router(), prefix=server_settings.api_prefix)
         self.mount_data_dir()
         self.mount_output_dir()
 

python/llama-index-server/llama_index/server/settings.py

@@ -11,6 +11,10 @@ class ServerSettings(BaseSettings):
         default="/api",
         description="The prefix for the API endpoints",
     )
+    workflow_factory_signature: str = Field(
+        default="",
+        description="The signature of the workflow factory function",
+    )
 
     @property
     def file_server_url_prefix(self) -> str:
@@ -40,6 +44,9 @@ class ServerSettings(BaseSettings):
         self.api_prefix = v
         self.validate_api_prefix(v)  # type: ignore
 
+    def set_workflow_factory(self, v: str) -> None:
+        self.workflow_factory_signature = v
+
     class Config:
         env_file_encoding = "utf-8"
 

python/llama-index-server/llama_index/server/utils/workflow_validation.py

@@ -0,0 +1,54 @@
+"""
+Utilities for validating workflow.py files (syntax and import checks only).
+"""
+
+import ast
+import importlib.util
+from typing import Optional
+
+
+def validate_workflow_file(
+    workflow_path: Optional[str] = None,
+    workflow_content: Optional[str] = None,
+    factory_signature: Optional[str] = None,
+) -> None:
+    """
+    Validate that the workflow file is syntactically correct, can be imported, and defines a callable factory function with the given name.
+    Raises an exception if invalid.
+    """
+    if workflow_path is None and workflow_content is None:
+        raise ValueError("Either workflow_path or workflow_content must be provided")
+
+    # 1. Syntax check
+    if workflow_path is not None:
+        with open(workflow_path, "r") as f:
+            content = f.read()
+    else:
+        if workflow_content is None:
+            raise ValueError(
+                "workflow_content must be provided if workflow_path is not specified"
+            )
+        content = workflow_content
+    try:
+        ast.parse(content)
+    except SyntaxError as e:
+        raise ValueError(f"Syntax error in workflow: {e}")
+
+    # 2. Import check (will catch missing modules, etc.)
+    spec = importlib.util.spec_from_file_location("workflow", workflow_path)
+    if spec is None or spec.loader is None:
+        raise ValueError(f"Could not load module specification for {workflow_path}")
+
+    mod = importlib.util.module_from_spec(spec)
+    try:
+        spec.loader.exec_module(mod)
+    except Exception as e:
+        raise ValueError(f"Import error: {e}")
+
+    # 3. Contract validation: require the given factory function name
+    if factory_signature:
+        if not hasattr(mod, factory_signature):
+            raise ValueError(f"Missing required function: '{factory_signature}'")
+        obj = getattr(mod, factory_signature)
+        if not callable(obj):
+            raise ValueError(f"'{factory_signature}' is not callable")