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[{"name":"session_id","description":"Specific session UUID to analyze (default: most recent log)","required":false},{"name":"output_path","description":"Where to write the analysis report (default: auto-generated)","required":false}]
error_handling
graceful
streaming
supported
verified
true
lastVerifiedAt
2026-03-05
source
builtin
trust_score
100
provenance_sha
6049916bac8e2632
Mode: Cognitive/Prompt-Driven — No standalone utility script; use via agent context.
Debug Log Analysis
Structured workflow for extracting actionable signal from Claude Code session debug logs. Use during reflection cycles, incident response, or when diagnosing agent failures.
When to Use
After any session with unexpected agent failures or stalls
When reflection-agent needs telemetry to contextualize task completions
When debugging hook errors that appear opaque in task outputs
When the router reports "agent completed but didn't call TaskUpdate"
Prerequisites
The scripts/reduce-debug-log.mjs script auto-detects the most recent log when no file argument is provided. It copies the log to .tmp/ and produces a reduced version there.
Step 0: Determine Analysis Mode
Two modes are available:
Auto mode (recommended): Let pnpm debug:reduce find and process the most recent log automatically.
Manual mode: Provide a specific session UUID or log file path.
Step 1: Locate and Reduce the Debug Log
IMPORTANT: Always find the most recent log dynamically. NEVER hardcode session UUIDs.
Auto mode (preferred)
# Auto-detect most recent log, copy to .tmp/, reduce in placecd /c/dev/projects/agent-studio && node scripts/reduce-debug-log.mjs 2>&1
# The script prints:# Auto-detected debug log: /home/user/.claude/debug/{session-uuid}.txt# Copied to: .tmp/{session-uuid}.txt# Original: N lines -> kept (issue-like): M -> ... -> after dedupe: K# Output: .tmp/{session-uuid}-reduced.txt
Capture the output paths from the script output for subsequent steps.
Manual mode (when a specific session is needed)
# List recent debug logs sorted by modification time (most recent first)ls -t "$HOME/.claude/debug/"*.txt 2>/dev/null | head -5
# Or on Windows (Git Bash):ls -t "/.claude/debug/"*.txt 2>/dev/null | -5
$USERPROFILE
head
Pick the target log path, then:
# Copy to temp (never operate on the original)mkdir -p .claude/context/tmp
cp"$HOME/.claude/debug/{session-uuid}.txt"".claude/context/tmp/debug-session-copy.txt"# Run reducer with explicit output path
node scripts/reduce-debug-log.mjs \
".claude/context/tmp/debug-session-copy.txt" \
--output ".claude/context/tmp/debug-session-reduced.txt"
Note any anomalies — e.g., if reduction is less than 90%, the session had unusually many errors.
Step 3: Read Reduced Log
Read .claude/context/tmp/debug-session-reduced.txt in full.
Step 4: Categorize Error Patterns in Reduced Log
For each line in the reduced log, classify into:
Category
Signal Pattern
Action
Hook Block (Write)
PreToolUse:Write + block
Count; find triggering agent + file path
Hook Block (TaskUpdate)
PreToolUse:TaskUpdate + burst
Count; find looping agent
Read Miss
File does not exist or placeholder text
Count; list missing files
Token Overflow
FileTooLargeError or token limit
Count; identify large files
Streaming Stall
Gap > 60s between log entries
Sum duration; note what preceded stall
Agent Drop
TaskUpdate not called or agent returned without completion
List by task ID
Tool Error
EISDIR, ENOENT, sibling tool call errored
Categorize by tool
Step 5: Cross-Reference Top Errors in Full Log
For the top 3 most frequent error categories:
Grep the FULL (unreduced) log copy for the error signature
Find the 10 lines before and after each occurrence
Identify: which tool call triggered it, which agent was running, what it was trying to do
# Use the full copy (not the original, not the reduced)
grep -n "PreToolUse:Write"".claude/context/tmp/debug-session-copy.txt" | head -30
grep -n "File does not exist"".claude/context/tmp/debug-session-copy.txt" | head -30
grep -n "timeout"".claude/context/tmp/debug-session-copy.txt" -i | head -30
Step 6: Cleanup Temp Files
After analysis, clean up the working copy (keep the reduced file for the report if needed):
rm -f ".claude/context/tmp/debug-session-copy.txt"# Optionally keep the reduced file for reference; delete when done# rm -f ".claude/context/tmp/debug-session-reduced.txt"
Step 7: Produce Structured Report
Write to .claude/context/reports/reflections/debug-log-analysis-{YYYY-MM-DD}.md:
<!-- Agent: reflection-agent | Skill: debug-log-analysis | Session: {YYYY-MM-DD} -->
# Debug Log Analysis — {YYYY-MM-DD}**Source log:** {path to original log — auto-detected or provided}
**Session UUID:** {session-uuid extracted from filename}
**Log statistics:**- Original: {N} lines / {bytes} bytes
- Reduced: {M} lines / {bytes} bytes
- Reduction ratio: {X}%
**Analysis timestamp:** {ISO-8601}
## Error Summary
| Category | Count | Severity | Root Cause |
| ------------------ | ----- | -------- | ---------- |
| Hook Block (Write) | N | CRITICAL | ... |
| Read Miss | N | HIGH | ... |
| ... | | | |
## Top 3 Deep Dives### 1. {Most frequent error}**Frequency:** N occurrences
**First occurrence:** line {N}, timestamp {T}
**Context:** {what the agent was doing}
**Root cause:** {why it happened}
**Fix:** {concrete recommendation}
### 2. ...### 3. ...## Observability Gaps Found
List any gaps where the log entry doesn't have enough info to diagnose the error.
## Recommendations- [ ] Immediate P0: {fix}
- [ ] P1: {fix}
- [ ] P2: {fix}
Known Observability Gaps (Agent-Studio v2026-02)
These gaps exist in the current debug log format:
Hook rejection body not logged — When unified-creator-guard.cjs blocks a Write, the rejection reason is not captured in the debug log. You see PreToolUse:Write blocked but not WHY.
Workaround: Check process.stderr output separately; or read the hook source to infer the rule that fired.
Agent identity missing from error lines — Error lines don't include which spawned agent caused the error.
Workaround: Correlate timestamps with task spawn/completion entries.
Read failure file path omitted — File does not exist lines don't always include the file path.
Workaround: Look at the preceding tool call line for the attempted path.
Streaming stalls unattributed — A 5+ minute stall appears as a timestamp gap with no context.
Workaround: The tool call preceding the gap is the likely cause.
No success logging — Only failures are prominent. Successful tool calls produce minimal log entries.
Workaround: Count total tool uses from task summary metadata.
Integration with Reflection
Reflection agents should invoke this skill for HIGH-priority reflection requests:
// In reflection agent, for high-priority triggers:if (priority === 'high' && debugLogPath) {
Skill({ skill: 'debug-log-analysis' });
// Include findings in reflection report
}
Iron Laws
ALWAYS copy the debug log before any analysis — never operate on the original file; in-place operations corrupt the forensic artifact.
NEVER report a root cause based on a single grep match — always read at least 10 lines of context before and after the match to understand what the agent was actually doing.
ALWAYS run the reducer script (Step 2) before attempting to read a full debug log — unfiltered debug logs contain 98%+ noise that obscures real signals.
NEVER skip the structured error report (Step 6) — an informal verbal summary is not a deliverable; the markdown report is required for reflection-agent to incorporate findings.
ALWAYS write new recurring error patterns to .claude/context/memory/issues.md — patterns not written to memory will recur invisibly across sessions.
Anti-Patterns
Anti-Pattern
Why It Fails
Correct Approach
Grepping the original log file directly
Modifies timestamps, corrupts forensic artifact, no rollback
