4. Debug Applications (Development stage)

Debug apps are applications used in the Platform, that are still in their initial stages of development. They allow developers to identify and resolve bugs, errors, and other technical issues that may arise during the development process. By using debug apps, developers can ensure that their applications are functioning as expected and provide a smooth and seamless user experience.

- Used for applications that have panels (UI).

4.1. Basic requirements

  • For working on dev/local environment, you will need to add local.dataloop.ai to your hosts file.

    • Open your hosts file with admin/sudo privileges. This is normally in /etc/hosts on Linux, C:\Windows\System32\drivers\etc\hosts on Windows. Add this line to the end of the file: local.dataloop.ai

    • You might also need to run your app in https mode.

  • You may need to enable CORS on your app.

  • Your app should be up running in the browser.

  • Your app should have a manifest file - dataloop.json - it needs to be publicly served under the app’s main address (For example: https://local.dataloop.ai:3000/dataloop.json).

  • You’re going to need a working, functioning Dataloop Platform user with a Developer role.

  • You’re going to need to be familiar with our Javascript SDK

4.2. How to add a debug app in the Dataloop Platform

  • On the left sidebar menu, go to Application Hub under the Application (FAAS) section, and open the ** Developer** tab. assets/apps/img.pngimg.png

  • Click the Add Function button.

  • Fill out the name of the app, choose a main slot and add your application’s URL address

    • (For example: https://local.dataloop.ai:3000) assets/apps/img_1.pngimg_1.png

  • Press the Create button, and wallah! You have a debug app in the Platform. assets/apps/img_2.pngimg_2.png

  • Go to the dataset browser, right-click on an item, Open With… and choose your app!

4.3. Tests

In order to run tests locally, you must mock the dl xFrame Driver and provide it with mock data. We created a DlMockDriver and a Debug Snapshot shortcut exactly for that!

  • The DlMockDriver is a mock driver that simulates the dl xFrame Driver, and is used for testing applications locally.

    • You can mock the window.dl during testing by assigning a new instance of DlMockDriver to global.window.dl, effectively overriding its original value.

  • In order to get the mock data for the mock driver, you can use the Debug Snapshot feature.

    • [Add a debug app to the Platform](index.md#How to add a debug app in the Dataloop Platform).

    • Press the Debug Snapshot icon at the top bar (or Alt+Shift+S) in order to download the generated snapshot file.

    • Place the file in your tests directory.

    • Require the snapshot file in your test file, and use it to create a new instance of DlMockDriver.

import { DlMockDriver } from '@dataloop/jssdk'

const data = require('./snapshot.json')
global.window.dl = new DlMockDriver(data)

4.4. Item Viewer Example

Here is an example of a basic Item Viewer App written in html & javascript (We trust that you’re better than us and can write better code than this using something like React/Vue etc.)

This following item viewer example supports images only.


<!DOCTYPE html>
<html lang='en'>

    <meta charset='UTF-8'>
    <meta http-equiv='X-UA-Compatible' content='IE=edge'>
    <meta name='viewport' content='width=device-width, initial-scale=1.0'>
    <title>Dataloop item viewer</title>

<button onclick='handleClick()'>refresh</button>
<button onclick='handleFetch()'>Fetch Item</button>
<button onclick='handleAnnotations()'>Fetch Annotations</button>
<br />
<input id='classification' type='text' />
<button onclick='handleCreate()'>Create Classification</button>
<div id='viewer-main'>
    <div id='tools-container'></div>
    <div id='item-container'></div>
    <div id='annotations-container'></div>

<script src='https://console.dataloop.ai/dlAppLib.js'></script>
    const annotationsDiv = document.getElementById('annotations-container')
    let item = null

    const handleClick = async () => {

    const maskIndex = (n) => {
        if (n >= 100) {
            return `${n}`
        } else {
            return n >= 10 ? `0${n}` : `00${n}`

    const handleFetch = async () => {
        const itemDiv = document.getElementById("item-container")
        itemDiv.innerHTML = ""
        item = await dl.items.get()
        const stream = await dl.items.stream(item.stream)
        const img = new Image(

        console.log("@@@@@", JSON.stringify(stream))
        img.src = stream

    const handleAnnotations = async () => {
        annotationsDiv.innerHTML = ""
        const annotations = await dl.annotations.query()
        const existingClasses = []
        for (const annotation of annotations.items) {
            const btn = document.createElement("button")
            btn.id = `annotation-${annotation.clientId}`
            const objectId = annotation.metadata.system.objectId
            btn.style.backgroundColor = annotation.labelColor
            btn.style.border = "0px"
            btn.style.marginRight = "4px"
            btn.innerText = `${annotation.label}#${maskIndex(objectId)} (${annotation.type

    const handleCreate = async () => {
        const label = document.getElementById("classification").value
        const classification = {
            type: "class",
            itemId: item.id,
            attributes: [],
            label: label,
        await dl.annotations.create(classification)

    const init = async () => {
        await dl.init()
        await dl.on('ready', async () => {
            await handleFetch()
            await handleAnnotations()
        dl.on('data', async (msg) => {
            if (msg.type === 'app') {
                if (msg.data.scope === 'annotation') {
                    const annotation = msg.data.data
                    if (msg.data.crud === 'created') {
                        await handleAnnotations()
                    } else if (msg.data.crud === 'deleted') {
                        if (!Array.isArray(annotation)) {
                            const annotationBtn = document.getElementById(`annotation-${annotation.clientId}`)?.remove()
                        for (const a of annotation) {
                            const annotationBtn = document.getElementById(`annotation-${a.clientId}`)?.remove()
            console.log('@@@@ Message from host agent:', msg)

<style lang='css'>
    .not-existing {
        background-color: white

    .existing {
        background-color: lightgreen


  "components": {
    "panels": [
        "name": "item-viewer",
        "supportedSlots": [
            "type": "itemViewer",
            "configuration": {
              "layout": {
                "leftBar": false,
                "rightBar": false,
                "bottomBar": false
        "conditions": {
          "resources": [
              "entityType": "item",
              "filter": {
                "metadata.system.mimetype": "image/*"
  • You may play with the slot’s layout to hide/show the different bars.

  • The conditions section is used to define the app’s supported items. In this example, we only support images.

  • You can find the full example (including how to publish and install the app) here!