# Web Chat UI
Pydantic AI includes a built-in web chat interface that you can use to interact with your agents through a browser.
For CLI usage with `clai web`, see the [CLI - Web Chat UI documentation](cli.md#web-chat-ui).
!!! note
The web UI is meant for local development and debugging. In production, you can use one of the [UI Event Stream integrations](ui/overview.md) to connect your agent to a custom frontend.
## Installation
Install the `web` extra (installs Starlette and Uvicorn):
```bash
pip/uv-add 'pydantic-ai-slim[web]'
```
## Basic Usage
Create a web app from an agent instance using [`Agent.to_web()`][pydantic_ai.agent.Agent.to_web]:
```python
from pydantic_ai import Agent
agent = Agent('openai:gpt-5.2', instructions='You are a helpful assistant.')
@agent.tool_plain
def get_weather(city: str) -> str:
return f'The weather in {city} is sunny'
app = agent.to_web()
```
Run the app with any ASGI server:
```bash
uvicorn my_module:app --host 127.0.0.1 --port 7932
```
## Configuring Models
You can specify additional models to make available in the UI. Models can be provided as a list of model names/instances or a dictionary mapping display labels to model names/instances.
```python
from pydantic_ai import Agent
from pydantic_ai.models.anthropic import AnthropicModel
# Model with custom configuration
anthropic_model = AnthropicModel('claude-sonnet-4-5')
agent = Agent('openai:gpt-5.2')
app = agent.to_web(
models=['openai:gpt-5.2', anthropic_model],
)
# Or with custom display labels
app = agent.to_web(
models={'GPT 5.2': 'openai:gpt-5.2', 'Claude': anthropic_model},
)
```
## Builtin Tool Support
You can specify a list of [builtin tools](builtin-tools.md) that will be shown as options to the user, if the selected model supports them:
```python
from pydantic_ai import Agent
from pydantic_ai.builtin_tools import CodeExecutionTool, WebSearchTool
agent = Agent('openai:gpt-5.2')
app = agent.to_web(
models=['anthropic:claude-sonnet-4-5'],
builtin_tools=[CodeExecutionTool(), WebSearchTool()],
)
```
!!! note "Memory Tool"
The `memory` builtin tool is not supported via `to_web()` or `clai web`. If your agent needs memory, configure the [`MemoryTool`][pydantic_ai.builtin_tools.MemoryTool] directly on the agent at construction time.
## Extra Instructions
You can pass extra instructions that will be included in each agent run:
```python
from pydantic_ai import Agent
agent = Agent('openai:gpt-5.2')
app = agent.to_web(instructions='Always respond in a friendly tone.')
```
## Reserved Routes
The web UI app uses the following routes which should not be overwritten:
- `/` and `/{id}` - Serves the chat UI
- `/api/chat` - Chat endpoint (POST, OPTIONS)
- `/api/configure` - Frontend configuration (GET)
- `/api/health` - Health check (GET)
The app cannot currently be mounted at a subpath (e.g., `/chat`) because the UI expects these routes at the root. You can add additional routes to the app, but avoid conflicts with these reserved paths.
## Custom HTML Source
By default, the web UI is fetched from a CDN and cached locally. You can provide `html_source` to override this for offline usage or enterprise environments.
For offline usage, download the html file once while you have internet access:
```python
from pydantic_ai.ui import DEFAULT_HTML_URL
print(DEFAULT_HTML_URL) # Use this URL to download the UI HTML file
#> https://cdn.jsdelivr.net/npm/@pydantic/ai-chat-ui@1.0.0/dist/index.html
```
You can then download the file using the URL printed above:
```bash
curl -o ~/pydantic-ai-ui.html <chat_ui_url>
```
Then use `html_source` to point to your local file or custom URL:
```python
from pydantic_ai import Agent
agent = Agent('openai:gpt-5.2')
# Use a local file (e.g., for offline usage)
app = agent.to_web(html_source='~/pydantic-ai-ui.html')
# Or use a custom URL (e.g., for enterprise environments)
app = agent.to_web(html_source='https://cdn.example.com/ui/index.html')
```
