runtime-logger

Runtime Activity Logger

Log key activities to .claude/logs/activity.log using bash as you work. This creates a trace of agent reasoning and actions analogous to info-level logging in deterministic code.

Setup

Before starting any task, ensure the log directory exists:

mkdir -p .claude/logs

Log Format

Use this consistent format for all log entries:

echo "[$(date -Iseconds)] [LEVEL] phase: message" >> .claude/logs/activity.log

Log Levels

When to Log

Task Lifecycle

• Task start: Log the goal and planned approach
• Task completion: Log summary, outcome, and any artifacts created

Tool Usage

• Before significant tool use: Log what tool and why
• After tool use: Log outcome (success/failure, key findings)

Decision Points

• Architectural choices: Log reasoning for design decisions
• Branch points: Log why one approach was chosen over alternatives
• Assumptions: Log any assumptions being made

Subagent Activity

• Delegation: Log task being delegated and to which subagent
• Completion: Log subagent results when they return

Examples

Starting a Task

echo "[$(date -Iseconds)] [INFO] start: Beginning refactoring task for payment module" >> .claude/logs/activity.log
echo "[$(date -Iseconds)] [INFO] planning: Will analyze current structure, identify patterns, then apply Strategy pattern" >> .claude/logs/activity.log

Tool Usage

echo "[$(date -Iseconds)] [INFO] tool: Reading src/payments/processor.py to understand current implementation" >> .claude/logs/activity.log
echo "[$(date -Iseconds)] [INFO] tool-result: Found 3 payment types with duplicated validation logic" >> .claude/logs/activity.log

Decision Points

echo "[$(date -Iseconds)] [INFO] decision: Using Strategy pattern - cleaner than inheritance for 3 payment types" >> .claude/logs/activity.log
echo "[$(date -Iseconds)] [INFO] decision: Keeping backward compatibility by wrapping legacy interface" >> .claude/logs/activity.log

Subagent Delegation

echo "[$(date -Iseconds)] [INFO] delegate: Spawning test-writer subagent for unit test coverage" >> .claude/logs/activity.log
echo "[$(date -Iseconds)] [INFO] delegate-complete: test-writer created 12 unit tests, all passing" >> .claude/logs/activity.log

Warnings and Errors

echo "[$(date -Iseconds)] [WARN] Found deprecated API usage in line 142, will need migration" >> .claude/logs/activity.log
echo "[$(date -Iseconds)] [ERROR] Build failed: missing dependency 'stripe-sdk', attempting to resolve" >> .claude/logs/activity.log

Task Completion

echo "[$(date -Iseconds)] [INFO] complete: Refactoring finished - 3 files modified, 12 tests added" >> .claude/logs/activity.log
echo "[$(date -Iseconds)] [INFO] artifacts: Created src/payments/strategies/*.py, updated tests/test_payments.py" >> .claude/logs/activity.log

Log File Management

Viewing Logs in Real-Time

tail -f .claude/logs/activity.log

Rotating Logs

For long-running projects, consider date-based log files:

echo "[$(date -Iseconds)] [INFO] message" >> .claude/logs/activity-$(date +%Y-%m-%d).log

Integration with Subagents

Subagents inherit access to bash and should follow the same logging conventions. When delegating tasks, instruct subagents to:

1. Log their start and completion
2. Use the same log file path
3. Prefix messages with their agent name for traceability

Example subagent log entry:

echo "[$(date -Iseconds)] [INFO] [test-writer] start: Generating unit tests for PaymentStrategy classes" >> .claude/logs/activity.log