Mods in Claude Code: change how Claude Code works

Summary
Anthropic developer advocate Lydia Hallie introduces and demonstrates "mods" for Claude Code, a new plugin-based extension system that lets developers alter how Claude Code functions internally. Mods are written in TypeScript and act as middleware running on Claude Code's internal event loop, enabling users to intercept tool calls, inject UI elements, customize prompts, and modify rendered output.

What is shown

• Overview of Mods & Architecture: Code in register.tsx demonstrating event listeners (on('ui.render'), on('prompt.submit'), on('tool.call')) manipulating Claude Code runtime behavior [00:06].
• Demonstrated Custom Mods:
  • context-bar: A live visual bar above the prompt breaking down context window usage (system prompt, tools, MCP tools, agents, memory files, skills, free space of a 1M token window) [00:17].
  • agents-panel: A sidebar listing all defined project agents (e.g., code-reviewer, docs-writer, perf-profiler) with single-click start buttons [00:26].
  • hide-email: An interface privacy filter that visually masks email addresses in Claude's output until hovered over [00:33, 02:49].
• Plugin Configuration: Setting up plugin.json and adding a "modules" field to hooks.json referencing TypeScript entry files [00:37].
• Middleware Pattern Explanation: Walkthrough of the ($, e, next) signature used by event hooks, detailing how `--- id: claude-mods-in-claude-code url: https://www.youtube.com/watch?v=yUuFvL1lK4k title: "Mods in Claude Code: change how Claude Code works" channel: "Claude" published: 2026-10-05 related_entries: [2026-10-01-claude-code-mods] kind: official added_by: "" description_status: pending views: 5249 views_checked: 2026-10-05

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