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

Anthropic released "Mods" for Claude Code, essentially 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, from tool calls and user prompts to UI rendering. That means developers can add custom panels next to the chat, intercept tool calls, or wire up entirely new commands. Some built-in features like the /diff command are already built as Mods, the company says.

Anthropic provides sample Mods on GitHub. Mods run with the user's permissions and aren't sandboxed, so Anthropic warns users to only install them from trusted sources. They work in the CLI, 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. You can turn it on with /plugin enable cc-plugin-you-should-know@builtin.

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