Subagents: one-off delegation that keeps your main context clean

A subagent is a fresh Claude instance that does a noisy, self-contained job in its own context window and hands back only the summary. Learn to delegate codebase searches and code reviews, restrict each agent's tools and model, and avoid the blank-context pitfall that produces confident wrong answers. Episode page & show notes Try a walking desk - stay healthy & sharp while you learn & code A subagent is a fresh Claude instance that does a self-contained job in its own context window and hands back only a summary. This episode covers using them the Act I way: one-off delegation to keep your main session's context clean. Why isolation matters. The context window fills fast and Claude's performance degrades as it does. From Anthropic's context-window walkthrough: a research subagent read ~6,100 tokens of files and returned a 420-token result. The reading never touched your main thread. The best-practices guide calls subagents one of the most powerful tools available because context is your fundamental constraint. The Agent tool. As of Claude Code 2.1.63 the Task tool was renamed to Agent (old Task(...) references still work as aliases). Subagents cannot spawn other subagents, which is why the orchestrator pattern needs agent teams later. Built-in subagents. Explore (read-only, Haiku, codebase search), Plan (read-only, used in plan mode), general-purpose (all tools, inherits your model), plus helpers statusline-setup and claude-code-guide. Explore and Plan skip CLAUDE.md and git status to stay fast. Custom subagents. Markdown files with YAML frontmatter in .claude/agents/ (project, checked into git) or ~/.claude/agents/ (user). The fields that matter: name, description (drives automatic delegation), tools (allowlist; omit to inherit all), and model (sonnet/opus/haiku/full ID/inherit). Manage them with the /agents command. See Create custom subagents. Proactive delegation. Put "use proactively" in the description field so Claude reaches for the agent on its own. Worked examples. A codebase-search delegation that keeps file reads out of your window, and the official read-only code-reviewer (restricted to Read, Grep, Glob, Bash) that judges your diff with fresh eyes. Subagent vs skill vs slash command. A skill runs in your main context; a subagent runs isolated and returns a summary; a slash command is a typed entry point. Offload noisy, self-contained work to a subagent. The pitfall. Subagents start blank, with no conversation history. Vague delegation produces confident, wrong answers. Scope tightly and restate load-bearing constraints. Plus the costs: tokens still get spent, cold-start latency, and no mid-task steering (a subagent can't even ask you a clarifying question).