How to build your own AI chatbot app (no code)

“Build me an AI assistant like ChatGPT” is one of the first things people try on App Builder Agent — and a chat app is a great first project, because the hard part (the model) is an API call away and the interesting part is the experience around it: personas, memory, voice, a focused use case.

This guide walks through a chatbot app that you can actually ship: a clean chat screen, conversation history, a few personas, and a settings screen for the API key. Along the way it covers the one thing most tutorials skip — where the key lives and why that matters.

What an AI chat app really needs

A chat screen alone is a demo. These are the pieces that turn it into something people keep on their phone:

• A message list that feels right — Bubbles, timestamps, streaming replies token by token, and a composer that grows with the text.
• Conversation history — Saved on the device: a list of past chats with titles, delete and rename. Users come back to old answers.
• Personas or modes — “Study tutor”, “Email writer”, “Travel planner” — each with its own system prompt. This is where your app stops being a generic clone.
• A clear place for the API key — A settings screen where the user pastes their own key (OpenAI, OpenRouter, Gemini…). Keys typed into an app are stored on that phone only.
• Error states — Out of credits, no network, key rejected — each needs a friendly message, not a spinner.
• Copy, share, regenerate — Small buttons under each answer that people use constantly.

Build it with App Builder Agent, step by step

You will describe the app, watch it run, and refine it. The agent handles the networking code and the streaming.

1. Start a mobile app project. Pick “Mobile app” so you can export an APK; a website version works the same if you prefer a link.
2. Describe the assistant and its personas. Name the model provider you intend to use, and be explicit that the user supplies their own key.
   Build an AI assistant app called Sable. Chat screen with streaming replies, a sidebar with saved conversations, and 4 personas: General, Study tutor, Email writer, Recipe helper. Settings screen where the user pastes their own OpenAI API key (stored on the device). Dark theme, purple accent.
3. Test with your own key. Open Settings in the simulator, paste a key, and chat. The agent will fix anything that fails; tell it exactly what you saw.
4. Add the features that make it yours. Voice input, image upload, a daily tip, a “favourite answers” list — one message each.
   Add a microphone button that transcribes speech into the composer, and a long-press on any answer to save it to a Favourites tab.
5. Export. Build the APK and install it. Because the key is entered by each user on their phone, you can share the app freely.

Prompts that work well

These prompts produce noticeably different apps — pick the one closest to your idea and change the details.

Make it feel finished

• Stream the replies. Waiting 20 seconds for a wall of text feels broken; words appearing one by one feels alive.
• Give every persona a real system prompt — the agent will write them if you describe the tone you want.
• Keep the free tier honest: if the app uses your key, add a daily limit or you will pay for strangers’ chats.
• Add a one-tap “New chat” button; users otherwise keep polluting one giant conversation.

Shipping an AI app safely

The APK export gives you an installable app in minutes. If each user brings their own key, there is nothing to run on a server and nothing to pay for. If you want a shared key so users don’t need one, ask the agent to deploy a small backend with the key kept server-side and a daily quota per user — the platform hosts that backend for you.

For a web version, publish the project to a link; the same chat UI works in any browser.

Frequently asked