A guide to ChatKit Theming / UI options for custom chatbots

Let’s be honest, a generic chat widget stuck on your website can feel a little... off. It often looks like a third-party tool that doesn't quite belong, and that can make customers hesitate. For people to actually trust and use an AI agent, it needs to feel like a natural part of your brand. The way it looks is just as important as what it knows.

This is where OpenAI's ChatKit comes in. It’s a component library built for developers who want total control over the look and feel of their AI chat UI. We’re going to walk through the world of ChatKit theming and its various UI options. We'll cover what you can do with it, explore some of the real-world limitations, and show you a faster route if you're a business that needs to get going without a massive engineering project.

What is OpenAI's ChatKit?

Think of ChatKit as a box of Lego bricks for building a chat window. It’s a pre-built set of JavaScript components (things like buttons, message bubbles, and text input fields) that developers can assemble to create the front-end of a chat interface. It’s designed to be the part your users see and interact with, while the AI "brains" you might build with OpenAI’s other tools do the thinking in the background.

It's meant for developers to embed directly into websites and apps, giving them deep control over every single pixel. You can dig into all the technical specs in the official ChatKit guide.

But here's the most important thing to understand: ChatKit is just a UI library. It's not a complete, out-of-the-box chatbot solution. It doesn't come with analytics, user management, or any business logic. You get the building blocks for the window, but you have to build the house and all the plumbing yourself.

Understanding the core ChatKit Theming / UI Options

This is usually the first stop on the customization journey. ChatKit gives you a solid set of basic options to make the chat widget match your brand’s visual identity.

Colors, fonts, and density

You can tweak several core theme properties to make the chat widget feel at home on your site. According to their API reference, the main levers you can pull are:

• Color Scheme: You can flip between light and dark modes to match your site's theme.

• Accent Colors: This lets you set a primary brand color for things like buttons, links, and other interactive elements.

• Typography: You can specify a font family so the text inside the chat matches the rest of your website.

• Density & Radius: These settings control the spacing and how rounded the corners are. You could go for a "compact" feel if you have a lot of information to show, or a more "comfortable," spacious look. The corner radius can also be adjusted to fit your brand’s style, whether it's sharp and modern or soft and friendly.

Customizing starters and text

Beyond just the look, you can change the default text to guide users more effectively right from the start.

You can swap out the generic "Welcome!" message and the "Ask anything..." placeholder in the text box. This is a small change, but it makes a big difference in setting the right context. For instance, a support bot could greet users with, "Hi! How can I help you today?" and have a placeholder that says, "Search for help with billing, features, and more..."

Another one of the most useful UI options is setting up starter prompts. These are suggested questions or actions that appear when a user opens a new chat. It’s a great way to show people what the agent can do, so they aren't left staring at a blank box, wondering what to type.

Beyond the basics: Advanced ChatKit Theming / UI Options

If you have a developer on hand, ChatKit lets you go much deeper to create some truly interactive and dynamic experiences.

Building custom layouts and widgets

This is where ChatKit starts to feel less like a chat window and more like a small application. The key concept here is "widgets." The official widget guide explains that widgets are the building blocks for constructing rich, interactive messages.

Instead of your AI agent sending back plain text, it can return structured components like Cards, Lists, Buttons, and Images. For example, imagine a user asks about a specific product. Instead of just getting a text description, the agent could send back a "Card" widget that includes:

1. An image of the product.

2. The product name as the title.

3. A short description.

4. A "Learn More" button that links directly to the product page.

All of this happens behind the scenes. The user's question goes to your AI agent, which fetches the product data and builds a JSON response that defines the widget. It sends this JSON back to ChatKit, which then renders it as a nice, clean interactive card in the chat window.

Adding custom buttons and attachments

You're not stuck with the default UI elements. Developers can add custom buttons to the chat header for actions like "Start a new chat," "Visit our help center," or "View my account."

You can also set up the chat composer to allow file attachments. This includes setting specific limits on file size, the number of files someone can upload, and the accepted file types (like PDFs or images).

While these advanced ChatKit UI options are pretty powerful, they come with a big catch: every custom action requires custom code. A developer needs to write an "onClick" handler for every single button and build a secure backend process to handle file uploads, which adds a whole new layer of work.

The hidden challenges of ChatKit

Okay, it’s time for some real talk about the trade-offs. The flexibility of ChatKit is its greatest strength, but for most businesses, it's also the source of its biggest headaches.

It's a developer tool, not a business solution

Every single change, from tweaking a button color to designing a complex widget, requires a developer who knows their way around JavaScript (and likely React). This immediately creates a bottleneck. Your marketing or support teams can't just hop in and make a quick text change; every request has to get in line for the engineering team.

There are also some hidden snags that can trip up even seasoned developers. For example, to get ChatKit to work at all, you have to configure a domain allowlist on OpenAI's platform. It's a necessary security step, but it's a common "gotcha" that can leave a team staring at a blank screen for hours, pushing back deadlines.

This is a world away from a self-serve platform. With a tool like eesel AI, you can connect your data sources, tweak your AI's personality, and deploy a fully working AI chatbot in minutes, all from a simple dashboard with no code needed.

The UI is just one piece of the puzzle

A beautiful chat window is pretty useless if the AI behind it can't actually help anyone. ChatKit only solves the front-end problem, leaving you to tackle the much harder parts of building a functional AI agent. Here’s what’s missing from the box:

• Knowledge Integration: ChatKit doesn't know where your company's information lives. There's no built-in way to connect it to your help articles in Zendesk, your internal wikis in Confluence, or the thousands of past support tickets that hold your team's collective wisdom. You have to build and maintain that entire data pipeline yourself.

• Business Logic: The UI can't take action on its own. If a user wants to check an order status, talk to a human agent, or get their issue routed to the right team, you need to custom-code all of that logic on your backend.

• Analytics: ChatKit gives you zero reporting. You won't have any idea what your users are asking, where the AI is falling short, or what gaps you have in your knowledge base. You're essentially flying blind.

Why a fully integrated platform is a better alternative

This is why an all-in-one platform makes more sense for most businesses. eesel AI handles both the UI and the AI logic, so it’s a complete solution right from the start.

It connects to all the tools you already use, like Google Docs, Slack, and past help desk conversations, to build a unified knowledge base. From there, you can create powerful, custom workflows without touching any code. You get full control over the AI's persona, what it knows, and the actions it can take, all from an easy-to-use dashboard.

Is ChatKit the right tool for your chatbot?

OpenAI's ChatKit gives developers a fantastic amount of flexibility to build a pixel-perfect, custom chat UI. Its ChatKit theming system and widget framework offer deep control over the front-end experience.

But all that control comes at a price: significant developer time, resources, and hidden complexity. It only handles the visual part of your chatbot, leaving you to build the critical backend infrastructure, knowledge integrations, and analytics on your own.

For businesses that need to get a powerful, on-brand, and effective AI support agent up and running quickly, a fully integrated platform is simply the more practical choice. It lets you focus on your business goals, not on a lengthy engineering project.

Ready to launch an AI agent that’s fully customized to your brand and ready to go in minutes, not months? Try eesel AI for free and see how easy it can be to automate support with a tool that’s built for results.