Monitor Tool

The Monitor tool spawns a background watcher and streams its events into the conversation as new transcript messages. Each event lands immediately and Claude reacts to it — no polling loop, no holding the turn open with a sleep.

Available since v2.1.98.

What It Does

Bash (sleep loop, polling)          Monitor tool
━━━━━━━━━━━━━━━━━━━━━━━           ━━━━━━━━━━━━━━━━━━━━━━
while true; do                     # Claude spawns a watcher
  check_ci_status                  # Watcher runs in background
  sleep 30                         # Each event → new message
done                               # Claude reacts immediately

The conversation stays open. Events arrive asynchronously. Claude processes each one and decides whether to act.

Common Use Cases

Tail a log file

> Tail server.log in the background and tell me the moment a 5xx shows up

Claude spawns a watcher on server.log. Each new log line arrives as a transcript message. When a 5xx pattern matches, Claude reacts immediately — describe the error, suggest a fix, or apply one automatically.

Watch CI on a PR

> Watch CI on my current branch and fix any failures as they come in

Claude monitors the CI status. When a check fails, it reads the failure output, writes a fix, and pushes — all without you sitting at the terminal.

Auto-fix dev server crashes

> Start the dev server in the background, watch for crashes, and restart and fix when it crashes

Claude starts the server, monitors its output, and when a crash appears, reads the traceback, patches the code, and restarts.

Training run progress

> Kick off training and summarize progress every epoch without keeping the session idle

Claude monitors training output and sends epoch summaries as events arrive.

/loop Self-Pacing

/loop now self-paces: if you omit the interval, Claude picks the next tick based on what it's waiting for. When the Monitor tool is available, Claude reaches for it instead of polling.

> /loop check CI on my PR

Claude will:

1. Use the Monitor tool to watch CI (not poll with sleep)
2. React the moment a result arrives
3. Schedule the next check only if the Monitor can't be used

Explicit interval (still works)

> /loop --interval 60 run the dependency audit

Dynamic (recommended)

> /loop check CI on my PR

Pairing Monitor with PreToolUse hooks

If you want to gate what Monitor can watch (e.g., only internal hosts):

{
  "hooks": {
    "PreToolUse": [{
      "hooks": [{
        "if": "Monitor(*)",
        "type": "command",
        "command": ".claude/hooks/monitor-allowlist.sh"
      }]
    }]
  }
}

#!/usr/bin/env bash
# monitor-allowlist.sh — only allow monitoring local files and localhost
set -euo pipefail
INPUT=$(cat)
TARGET=$(echo "$INPUT" | jq -r '.tool_input.target // ""')

case "$TARGET" in
  *.log|localhost:*|/tmp/*)
    echo '{"decision": "approve"}'
    ;;
  *)
    jq -n --arg t "$TARGET" '{"decision":"block","reason":("Monitor target not allowed: "+$t)}'
    ;;
esac

Decision: Monitor vs Bash Loop vs ScheduleWakeup

Scenario	Best Tool
React to log events in real time	Monitor tool
Wait for a known-duration process (8-min build)	ScheduleWakeup (~270s, stays in cache)
Poll a REST endpoint every minute	Monitor tool (wrap in a watcher script)
Long-idle background check (>30 min)	ScheduleWakeup (1200s+)
One-shot process check on demand	Bash

Available in

• CLI (v2.1.98+)
• Desktop app
• Not available in -p (print/pipe) headless mode