Live HTML in Copilot CLI

In How to extend Copilot CLI with custom UI, Steve Sanderson demonstrates how to create a Copilot CLI extension: a javascript module that runs within the CLI and adds tools the agent can call. One example opens a webview whose contents are controlled by the agent, such as a clock or a live stream of events from the Copilot harness.

Note: “extensions” are currently an experimental feature and need to be enabled with /experimental on.

He’s also generalized this into a webview creator plugin. You install the plugin to get the skill, then invoke the skill to scaffold an extension for your needs. It includes useful module files as templates that can be included/reused in the resulting extension to save some work.

Note: a “plugin” is an installable package that extends Copilot CLI with reusable agents, skills, hooks, and MCP/LSP configurations.