Cost Alert Monitor

NotificationIntermediateHook Type: notification

Cost Alert Monitor tracks cumulative token usage throughout a Claude Code session using notification events. It maintains a running tally of input and output tokens, calculates estimated costs based on current pricing, and triggers alerts at configurable thresholds (50%, 75%, 90% of budget). When a threshold is crossed, it displays a prominent warning with usage details and remaining budget. The hook also logs per-session cost summaries for historical tracking and monthly roll-up reports.

costbudgettokensmonitoringalerts

Hook Code

#!/bin/bash
# Cost Alert Monitor Hook
# Tracks token usage and alerts on budget thresholds

COST_FILE="${HOME}/.claude/cost-tracker.json"
DAILY_BUDGET=5.00  # USD
ALERT_THRESHOLDS="0.50 0.75 0.90"

# Initialize cost file if missing
if [ ! -f "$COST_FILE" ]; then
  echo '{"date":"","input_tokens":0,"output_tokens":0,"alerts_sent":[]}' > "$COST_FILE"
fi

TODAY=$(date +%Y-%m-%d)
CURRENT_DATE=$(jq -r '.date' "$COST_FILE")

# Reset daily counters if new day
if [ "$TODAY" != "$CURRENT_DATE" ]; then
  echo "{"date":"$TODAY","input_tokens":0,"output_tokens":0,"alerts_sent":[]}" > "$COST_FILE"
fi

# Parse token counts from notification
INPUT_TOKENS=$(echo "$NOTIFICATION_DATA" | jq -r '.input_tokens // 0')
OUTPUT_TOKENS=$(echo "$NOTIFICATION_DATA" | jq -r '.output_tokens // 0')

# Update cumulative counts
jq --argjson inp "$INPUT_TOKENS" --argjson out "$OUTPUT_TOKENS"   '.input_tokens += $inp | .output_tokens += $out' "$COST_FILE" > "$COST_FILE.tmp"   && mv "$COST_FILE.tmp" "$COST_FILE"

# Calculate estimated cost (Claude Sonnet pricing)
TOTAL_INPUT=$(jq '.input_tokens' "$COST_FILE")
TOTAL_OUTPUT=$(jq '.output_tokens' "$COST_FILE")
COST=$(echo "scale=4; $TOTAL_INPUT * 0.000003 + $TOTAL_OUTPUT * 0.000015" | bc)
RATIO=$(echo "scale=4; $COST / $DAILY_BUDGET" | bc)

# Check thresholds
for THRESHOLD in $ALERT_THRESHOLDS; do
  ALREADY=$(jq -r --arg t "$THRESHOLD" '.alerts_sent | index($t) // empty' "$COST_FILE")
  if [ -z "$ALREADY" ] && [ "$(echo "$RATIO >= $THRESHOLD" | bc)" -eq 1 ]; then
    PCT=$(echo "scale=0; $THRESHOLD * 100 / 1" | bc)
    echo "COST ALERT: ${PCT}% of daily budget reached ($$COST / $$DAILY_BUDGET)"
    echo "  Input: $TOTAL_INPUT tokens | Output: $TOTAL_OUTPUT tokens"
    jq --arg t "$THRESHOLD" '.alerts_sent += [$t]' "$COST_FILE" > "$COST_FILE.tmp"       && mv "$COST_FILE.tmp" "$COST_FILE"
  fi
done

exit 0

Add this hook to your Claude Code settings or .claude/settings.json to activate.

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Cost Alert Monitor

About Cost Alert Monitor

Claude Code hooks let you run custom shell commands automatically in response to specific events during Claude's operation. Cost Alert Monitor is a Notification hook at the Intermediate level that automates tasks at key moments in your development workflow, reducing manual steps and enforcing consistency across your team.

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