Claude Code's new Mods system lets developers rewrite the AI coding tool from the inside

Anthropic has released a "Mods" system for Claude Code, described as middleware that runs directly inside the tool. The plugin-based system lets developers change how Claude Code looks and works.

Mods are JavaScript or TypeScript functions that hook into specific events, including tool calls, user prompts and UI rendering. According to the description, developers can add custom panels next to the chat, intercept tool calls, or wire up entirely new commands. Anthropic says some built-in features, such as the /diff command, are already built as Mods.

Sample Mods are available on GitHub. Mods run with the user's permissions and are not sandboxed, so Anthropic warns users to only install them from trusted sources. They work in the CLI and the desktop app, and partly in the VS Code extension. Organizations can control which Mods are allowed to load.

The first official Mod plugin is called "You Should Know." It spins up a separate agent that watches Claude's output and sends a "Heads up" message when it spots important information users might have missed. It can be enabled with the command /plugin enable cc-plugin-you-should-know@builtin.