root-cause-analyzer

root-cause-analyzer is a skill for Claude Code from davidmatousek/tachi. It costs 68 tokens per session (2,776 once invoked), scanned A, original, Apache-2.0.

A structured debugging guide based on the 5 Whys method, which repeatedly asks why a problem happened until its underlying cause is clearer.

In plain words
What is it for?
Use it to investigate complex or repeated problems, record the findings in development documentation, and update the team knowledge base with the resulting solution.
Why use it?
It helps distinguish symptoms from recurring causes and checks the knowledge base for an existing solution before starting a new investigation.

Skill for Claude Code

Written for Claude Code: installed under .claude/. Also seen: names the TodoWrite tool; mentions Claude Code.

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/davidmatousek/tachi/root-cause-analyzer
Any agent
npx skills add davidmatousek/tachi --skill root-cause-analyzer
Clone the repo
git clone --depth 1 https://github.com/davidmatousek/tachi

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for root-cause-analyzer

README.md
[![agentmods](https://agentmods.dev/badge/skills/davidmatousek/tachi/root-cause-analyzer.svg)](https://agentmods.dev/skills/davidmatousek/tachi/root-cause-analyzer)
Your own site
<a href="https://agentmods.dev/skills/davidmatousek/tachi/root-cause-analyzer"><img src="https://agentmods.dev/badge/skills/davidmatousek/tachi/root-cause-analyzer.svg" alt="Measured on agentmods" height="20"></a>
Per session 68 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,776 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00068 $0.02776
Opus 5 $0.00034 $0.01388
Sonnet 5 $0.00014 $0.00555
Haiku 4.5 $0.00007 $0.00278

Measured 6d ago against content hash b8614825c578, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

root-cause-analyzer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

.claude/skills/root-cause-analyzer/SKILL.md · 409 lines

How it starts

The opening of the file, as written. The whole thing — 409 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Root Cause Analyzer Skill

Purpose

Systematically identifies root causes of complex problems using the 5 Whys methodology from docs/5-WHYS-METHODOLOGY.md. Documents findings in docs/development-learnings/ and updates Knowledge Base (docs/kb/) using make kb-pattern. Implements FR-009 from the feature specification.

Knowledge Base Integration

IMPORTANT: Before starting root cause analysis, check the Knowledge Base for existing patterns.

Pre-Analysis KB Check

from scripts.kb.search import kb_search, kb_get_pattern

# Search for similar issues
results = kb_search(
    query="[error message or symptom]",
    category="[ARCH/DB/API/TEST/etc]",
    min_quality_score=60,
    limit=5
)

if results:
    print(f"Found {len(results)} existing patterns!")
    # Review top pattern
    pattern = kb_get_pattern(results[0].id)
    if pattern:
        # Apply existing solution instead of re-analyzing
        print("Applying existing root cause analysis from KB")
else:
    print("No existing patterns found. Proceeding with new 5 Whys analysis")

When to Check KB

  1. Before starting 5 Whys: Search for error messages, symptoms, or similar problems
  2. During analysis: Browse relevant categories (ARCH, DB, API, TEST, ERROR) for design patterns
  3. After finding root cause: Search again to see if this is a known systemic issue
  4. Before documenting: Check if similar pattern exists to avoid duplication

What to Search For

  • Exact error messages: Copy error text into search query
  • Symptom keywords: "timeout", "connection pool", "race condition", etc.
  • Technology + problem: "postgresql connection pool exhausted"
  • Pattern category: Use category filter to narrow results

If Pattern Found

  1. Review the existing pattern's 5 Whys analysis
  2. Check if root cause matches current issue
  3. Apply existing solution if applicable
  4. Update pattern usage count if applied
  5. Add cross-reference in your documentation

If No Pattern Found

Read the full file on GitHub · 409 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 6d ago First seen · 409 lines · 68 tokens per session scan A b8614825c578

Subscribe to this mod's changes

root-cause-analyzer is a skill published in the GitHub repository davidmatousek/tachi (90 stars, last pushed 24d ago), licensed Apache-2.0. It adds 68 tokens to every session and 2,776 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.