Claude Code Background Agents

Claude Code Background Agents and Tasks

When to use: Background Bash via Ctrl+B or run_in_background=true, /loop with fixed or self-paced intervals, Monitor tool for streaming output, Agent view (claude agents) for parallel sessions, subagents for side tasks, workflows for multi-agent orchestration, /schedule (cloud routines), and /goal for turn-by-turn looping.

Quick Summary

Background Bash: Run a shell command asynchronously. Press Ctrl+B during a Bash tool call, or Claude sets run_in_background=true. Command runs; output written to file in session directory. Claude reads output with Read tool. Returns task ID. List and stop with /tasks.

/loop: Recurring prompt on a session-scoped schedule. Fixed interval (5m, 30s) or self-paced. Behind the scenes uses CronCreate/CronList/CronDelete tools. Expires 7 days or when you Esc.

Monitor: Built-in tool; streams background script output line-by-line as each line arrives. Claude reacts mid-conversation without polling. Not available on Bedrock/Vertex/Foundry. More token-efficient than /loop on fixed cron.

Agent view (claude agents): Dispatch and monitor independent background sessions in a dedicated terminal UI. Each session isolated, gets its own worktree. Survives terminal exit (supervisor process keeps them alive). You hand off work; Claude runs autonomously.

Subagents: Spawn a worker inside conversation with separate context. Foreground subagents show permission prompts as they run; background subagents don't and auto-deny unpermitted calls. Returns summary. Does not block main turn.

Workflows: JavaScript script runs in background, orchestrates many subagents. Script holds plan; intermediate results stay out of context. Resumable. Invoke via /workflows or ultracode effort level.

/schedule (cloud routines): Create a task on Anthropic infra. Cron or API trigger. Persists independently of any session.

/goal: Keep session looping turn-by-turn until a condition is met. Session stays active.

Background Bash Commands

When: Long builds, test suites, dev servers, file watches.

How to invoke:

1. Press Ctrl+B during a Bash tool call to move it to background.
2. Or: Claude sets run_in_background=true on the Bash tool parameter.

Behavior:

• Command runs asynchronously. Claude gets back task ID immediately.
• Output written to file in session directory.
• Claude reads output later with Read tool (no blocking).
• Max 30,000 chars per command before file save + preview. 5GB hard output cap before auto-termination.
• Auto-cleaned on session exit.
• List and stop: /tasks command.
• Disable: CLAUDE_CODE_DISABLE_BACKGROUND_TASKS=1.

Key constraint: Background Bash does NOT re-invoke Claude on completion. You or a scheduled /loop must poll or read the output file.

/loop: Local Recurring Prompts

Scope: Session-local. Expires 7 days or Esc. Restored on --resume if unexpired.

Three modes:

Mode 1: Fixed Interval + Prompt

/loop 5m check if deployment finished

• Interval: s, m, h, d. Converts to cron; Claude confirms actual schedule.
• Fires between turns, never mid-response. If Claude busy, waits for turn end.
• Jitter: up to 30 minutes after scheduled time (deterministic per task ID to prevent API thundering).

Mode 2: Prompt Only (Self-Paced)

/loop check whether CI passed and address review comments

• Claude chooses delay 1m–1h after each iteration based on observed work.
• May use Monitor tool instead to avoid re-polling.
• Respects 7-day expiry.
• Bedrock/Vertex/Foundry: unsupported; falls back to fixed 10m instead.

Mode 3: Bare /loop (Fixed Built-in Maintenance)

/loop
/loop 15m

• Bare /loop = built-in maintenance prompt on fixed cron (NOT self-paced). Customizable via .claude/loop.md or ~/.claude/loop.md.
• Bedrock/Vertex/Foundry: bare /loop prints usage instead.

Stop: Press Esc (works only during wait). Fixed-cron tasks keep running. Self-paced /loop may stop itself if work complete.

Under the hood: CronCreate, CronList, CronDelete tools. Max 50 tasks per session.

Monitor Tool

What: Streams background script output line-by-line without polling.

When: More token-efficient alternative to /loop fixed intervals. Claude may choose Monitor for self-paced /loop instead of cron.

How: Claude runs script in background; yields each output line as it arrives. Claude reacts to each line immediately.

Availability: Not on Bedrock/Vertex/Foundry.

Agent View: Background Sessions

Command: claude agents (opens dedicated terminal UI).

What: One screen for all dispatched background sessions. Each is a full Claude Code session, independent, with its own worktree.

How to dispatch:

• From agent view: type prompt, press Enter.
• From inside session: /background [prompt] or /bg [prompt].
• From shell: claude --bg "<prompt>".

Behavior:

• Each session isolated (edits go to separate worktree under .claude/worktrees/).
• You hand off; Claude runs autonomously.
• Status at a glance. Attach/peek/reply without leaving agent view.
• Supervisor process keeps sessions alive after terminal exit. Restart machine requires claude respawn <id> recovery.

Subagents (In-Session Delegation)

Scope: Inside one conversation. Spawned by Claude or via /agents command.

Permission behavior (critical distinction):

• Foreground subagents: Show permission prompts as they run (same as main session).
• Background subagents: Don't show prompts; inherit permissions already granted; auto-deny unpermitted calls and keep going.

Behavior:

• Runs in own context.
• Returns summary to main conversation.
• Does not accept new user input mid-task.
• Can inherit full tool access or restricted set.

When: Side research, exploration, parallel investigation.

Dynamic Workflows

What: JavaScript script orchestrates many subagents in background. Script holds plan; intermediate results stay out of context.

When: Large audits, 500-file migrations, cross-checked research, multi-angle planning.

How: Mention ultracode keyword or ask Claude to write workflow. Script executes in background. Monitor with /workflows. Final report to session when done.

Resumable: Pause/resume within same session. Exit Claude Code = fresh restart next session.

/schedule: Cloud Routines

Scope: Persists on Anthropic infra, independent of any session. Survives machine restart.

Triggers: Cron schedule, API call, GitHub event.

vs /loop: /loop session-local, fires only while Claude running locally. /schedule runs in cloud.

/goal: Turn-by-Turn Looping

What: Keep session actively looping until condition is met.

How: /goal all tests pass and code is deployed

Behavior: Claude evals condition after each turn. Session stays awake.

Comparison Table: When to Use

Polling Without Re-Running Claude

Pattern: Bash loop + file writes → Claude reads file periodically.

while true; do
  curl https://api.example.com/status > /tmp/status.json
  sleep 30
done

Claude runs in background. Claude reads /tmp/status.json later. No re-invocation.

Better: Use Monitor or /loop if Claude should react, or /goal for tight feedback.

Key Constraints

1. Background Bash does not re-invoke Claude. Poll with /loop, Monitor, or read file.
2. Subagents: foreground shows prompts; background doesn't. Critical for permission handling.
3. Agent view sessions are discrete. Separate worktrees; don't see main conversation.
4. Scheduled tasks (cron) expire 7 days. Extend by recreating, or use /schedule for durable cloud tasks.
5. /loop fires between turns, never mid-response. If Claude busy, waits for turn end.
6. Jitter deterministic per task ID. Prevents API thundering at wall-clock moments.
7. Monitor not on Bedrock/Vertex/Foundry. Use /loop instead.

Common Patterns

Watch a deploy: /loop 2m did deployment finish? if so, run smoke tests

Babysit a PR: /loop check CI status and new review comments; address them

Audit entire codebase: ultracode: audit every function in src/ for missing error handling

Parallel research: Dispatch three independent investigations via agent view, review findings.

Continuous improvement: /goal all tests pass and code is deployed

Monitoring Active Work

• Background Bash: /tasks command shows running tasks.
• /loop: /tasks shows scheduled tasks.
• Agent view: claude agents opens UI.
• Subagents: /agents shows Running tab.
• Workflows: /workflows shows phases, agent counts, token totals.

Token Costs

• Background Bash: runs locally, no ongoing tokens.
• /loop fixed: one prompt per fire, cache reuse.
• /loop self-paced: one prompt per iteration, Claude chooses delay.
• Monitor: streaming; efficient vs polling.
• Agent view: each session fresh context, multiplies tokens.
• Subagents: separate context per agent.
• Workflows: many agents; estimate before large run.
• /schedule (cloud): billed separately, runs independently.