Claude Fable 5 just dropped and I'm running it across every repo I own.
I ship 4 products solo. I don't have time to manually review tech debt — so I made the new model do it.
This prompt audits your entire codebase like a principal engineer would: maps it, finds the ugly parts, rates everything by severity, and hands you a prioritized task plan with effort estimates.
Copy-paste it into Claude Code on any repo that matters to you:
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Repo Audit & Improvement Plan
You are a world-class principal-level software engineer and technical auditor. Deeply analyze this repository, produce an honest audit, and deliver a prioritized, actionable improvement plan. Work in the four phases below, in order. Do not skip ahead.
Ground every claim in actual files: cite file paths and line numbers. If you can't verify something, say so explicitly rather than guessing.
Phase 1 — Discovery & Mapping (read before judging)
- Map the directory structure, project type, languages, frameworks, runtime targets
- Identify entry points, core modules, and the main data/control flow
- Read package manifests, lockfiles, build config, CI config, env files, and docs
- Determine what the project is for: purpose, intended users, maturity level
- Note existing conventions so recommendations fit the culture instead of fighting it
Output: a concise "Repo Map" — purpose, stack, architecture sketch, key directories, and anything that surprised you.
Phase 2 — Audit (evidence-based, severity-rated)
For every finding record: what you found, where (file:line), why it matters, and severity (Critical/High/Medium/Low). Audit:
- Architecture & design: coupling, circular deps, god files, layering violations, scalability bottlenecks
- Code quality: duplication, dead code, complexity hotspots, swallowed exceptions, type safety holes
- Security: hardcoded secrets, injection risks, missing validation, auth weaknesses, deps with known CVEs
- Testing: coverage gaps around core business logic, tests that assert nothing, missing test types
- Performance: N 1 queries, blocking calls in async paths, missing caching, unbounded growth
- Dependencies: outdated, unmaintained, or unnecessarily heavy packages; lockfile hygiene
- DevEx & ops: build friction, CI/CD gaps, logging/observability, deployment story
- Docs: README accuracy, stale docs that contradict code
Rules: prefer 15 high-confidence findings over 50 speculative ones. Label facts vs. judgments. List strengths too. Don't forget the ugly parts that need utmost priority.
Phase 3 — Improvement Strategy
- Identify the 3–5 themes that explain most findings
- For each theme: target state the principle behind it
- State what you're NOT fixing and why (effort vs. payoff)
- Define "done" with measurable signals (e.g., "CI fails on lint errors," "core coverage >= 80%")
Phase 4 — Detailed Task Plan
Break work into discrete tasks, each with: title description, files affected, acceptance criteria, effort (S = <2h, M = half-day, L = 1–2 days, XL = needs breakdown), risk, and dependencies. Order into milestones:
- Milestone 0 — Safety net: tests around critical paths, CI gates, backups
- Milestone 1 — Critical fixes: security and correctness
- Milestone 2 — High-leverage improvements that make all future work easier
- Milestone 3 — Quality & polish
Flag quick wins (high impact, S effort) separately. Include implementation sketches for the top 3 tasks.
Final deliverable: one document — Executive Summary (health grade A–F, top 3 risks, top 3 opportunities), Repo Map, Audit Report, Improvement Strategy, Task Plan, Open Questions.
Constraints: Do NOT modify any code. Analysis only. Don't pad the report — if a dimension is healthy, say so in one sentence and move on. Calibrate to the project's maturity. If the repo is large, go deep on the core 20% that does 80% of the work.
Introducing Claude Fable 5: a Mythos-class model that we’ve made safe for general use.
Its capabilities exceed those of any model we’ve ever made generally available.