premortem

A Claude Code skill that runs a structured premortem on a concrete plan, launch, hire, or decision — finds in 10–15 minutes the holes that would otherwise show up only after the failure.

Russian / Русский

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Why this exists

You ship a product — feels well thought out. Three months later it's dead. And the whole way through, Claude was cheerfully nodding: "yeah, solid plan, good luck!"

That's not a bug in any specific model. It's the default behaviour of all LLMs. Ask "what could go wrong?" and you get hedged, polite, generic risk lists. Ask "is this a good plan?" and the model finds reasons to say yes.

Premortem breaks the pattern. Not "evaluate this plan," but "imagine the plan has already failed — explain how it died." The model switches into narrative mode and produces concrete, creative, honest causes instead of hedging.

Mitchell, Russo & Pennington (1989) measured ~30% more specific causes of future outcomes under past-tense framing than under conditional framing. Kahneman called premortem his single most valuable decision-making tool.

This skill ports the method into Claude Code as a reproducible session with deterministic mechanics and persistent history.

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What it does

The session has four phases:

• Pre-flight — syncs context with what the project already knows (CLAUDE.md, attached briefs), only asks for what's missing.
• Silent scan — three parallel helpers look at the plan from six angles (Customer, Operator, Adversary, Assumptions, situational angle, and always "Future Maintainer" for the WYSIATI micro-step). Semantic dedup leaves 5–8 unique holes.
• Live dialog — for each hole the skill proposes 2–3 strategic options, the user picks one. The top 1–3 are expanded to full mode (prevent / detect / stop condition / limit damage).
• Persist — atomic write to docs/premortem/<plan-name>.md plus a snapshot in history/. A month later you can re-run premortem on the same plan and compare: which holes closed, which got worse, which are new.

Built into the synthesis: outside view (Kahneman & Lovallo 2003), bias scan with 6 items from the Kahneman/Lovallo/Sibony HBR 2011 checklist, and a conditional reverse-premortem (Klein 2025) when the recommendation is delay/abort — countering the over-cautious bias of pure premortem.

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How it works

Phase 1. Pre-flight (1–2 min)

The skill first scans available context — what's already in the chat or in project files. It only asks for what's missing. Minimum to start:

• subject (what's launching / being decided)
• audience
• success criterion
• evaluation horizon (30 days / 3 months / 12 months / after pilot / after launch)

Reference class is asked separately: "What does this resemble from projects already done?" — the foundation for the outside view.

Phase 2. Silent scan (3–5 min)

The skill classifies the plan type and picks 6 angles for it. Three parallel LLM helpers run in one message (2 angles each). Each returns up to 2 holes with a confidence marker: "backed by context" / "needs verification" / "assumption."

Hash dedup removes obvious duplicates; semantic dedup merges close holes while preserving sources. Result: 5–8 unique holes, sorted by importance × confidence.

The user only sees the chosen angles in one line, then the prepared list of holes.

Phase 3. Live dialog (5–8 min)

For each hole:

1. Description in one paragraph + why it matters + angle + confidence.
2. 2–3 strategic options with +/–. Directions, not tasks.
3. User picks / asks for other options / defers / rejects.
4. For the chosen option: what we picked, why, first step, owner (agent / human / both).

After all holes:

• The skill picks the top 1–3 by importance × reversibility × confidence.
• The top is expanded to full mode: prevent / detect / stop condition / limit damage.
• Bias check on the top. The skill proposes the most likely cognitive bias that may have distorted the decisions, and a concrete correction.
• Session recommendation: continue / reduce_stake / delay / abort — based on the pattern of accepted decisions.
• Reverse premortem runs only on reduce_stake / delay / abort: "the horizon passed. We didn't do it. Turned out to be a mistake — why?" Counter to the over-cautious pull of pure premortem.

Phase 4. Persist (1 min)

One main file at docs/premortem/<slug>.md plus a timestamped snapshot in docs/premortem/history/. Writes are atomic (tempfile + os.replace

• fsync) under an advisory file lock. Any sequence of runs leaves the file valid.

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What you get

A single markdown file with YAML frontmatter:

• Context: subject / audience / success / horizon / reference class
• Holes (5–8): id, title, angle, importance, confidence, status, description, accepted decision
• Top 1–3 holes in full mode: prevent / detect / stop / limit damage, owner, first step
• Bias check in one line
• Session recommendation + reason
• Reverse premortem (when applicable): 3 reasons "why we may have been wrong not to do it" + what tips the balance
• Run history with status dynamics: same / worse / resolved / new

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When to use

The skill works on concrete, reversible commitments with a high cost of being wrong. Good cases:

• Product / feature launch. "Shipping the new dashboard in 6 weeks."
• Pricing change. "Bumping the subscription from $19 to $39."
• Hire. "First marketing hire, junior, $60k base."
• Content launch. "$297 live workshop on [topic] for [audience]."
• Architecture decision. "Migrating monolith to microservices in a quarter."
• Partnership / contract. "Signing a 12-month exclusive with one distribution channel."

Minimum requirements: there's a plan with shape (not an idea in your head), you have 10–15 minutes, the commitment isn't finalized yet.

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When NOT to use

• Idea without shape. Nothing to break — help draft the plan first, then premortem.
• Question with one right answer. "Which model is faster?" — that's fact-check, not premortem.
• Creative editing of a draft. That's editing, not premortem.
• Already-irreversible decision. Premortem can't roll it back.
• Multi-perspective input on a present-tense decision. LLM Council pattern fits better than past-tense framing.

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Recommendations

• Run when the plan is "almost ready." Too early — nothing to break. Too late — you can't influence anything.
• Don't skip reference class. "What does this resemble from done projects?" is the cheapest source of outside view. If you don't know — say so, the skill moves on with empty reference class.
• Don't default to "defer." Premortem systematically biases toward caution (Klein 2025). That's why reverse-premortem is built in: it asks "what if we were wrong NOT to do it?"
• Re-run after a month. History compares — which holes closed, which got worse, which are new. Catches plan drift.
• Don't run premortem on someone else's plan without context. Get at least subject / audience / success first. Without that you'll get a generic risk checklist, not premortem.
• Accept 2–3 decisions, not 8. If the skill produces 8 holes and you accept all of them, it's likely an illusion of control. Premortem worked when the top is chosen and there's a concrete first step.

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Installation

Requirements:

• Claude Code
• Git
• uv — runs the CLI scripts (deterministic mechanics)

Install:

git clone https://github.com/AndyShaman/premortem.git
cd premortem
./install.sh

The installer copies premortem/ (SKILL.md, scripts, references, assets, evals) to ~/.claude/skills/premortem/. Tests stay in the repo.

Verify:

ls ~/.claude/skills/premortem/SKILL.md

Restart Claude Code (or start a new session) — the skill loads automatically on trigger phrases.

Update:

cd premortem
git pull
./install.sh

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Triggers

The skill auto-loads on phrases like:

• "premortem", "premortem this", "run premortem"
• "find holes in this plan"
• "look at this plan from the outside"
• "what could kill this [plan]?"
• "what am I missing in [plan]"
• "future-proof this [plan/launch]"

Example prompts:

• "premortem this: launching a $297 live workshop on Claude Cowork for marketing teams"
• "stress-test this hire — first marketing person, junior, $60k base"
• "find holes — shipping the new pricing in 2 weeks"

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Method origins

• Gary Klein, Performing a Project Premortem, HBR, 2007
• Klein, Sources of Power, MIT Press, 1998 — mental simulation, RPD
• Klein, The Pre-Mortem Method, Psychology Today, 2021 — action round
• Klein, Double-Barreled Pre-Mortems, Psychology Today, 2025 — reverse premortem
• Mitchell, Russo & Pennington, Back to the Future: Temporal Perspective in the Explanation of Events, JBDM, 1989 — prospective hindsight
• Veinott, Klein & Wiggins, Evaluating the Effectiveness of the PreMortem Technique, ISCRAM, 2010 — empirical validation
• Kahneman, Thinking, Fast and Slow, 2011, ch. 23–24
• Kahneman & Lovallo, Delusions of Success, HBR, 2003 — outside view
• Kahneman, Lovallo & Sibony, Before You Make That Big Decision, HBR, 2011 — 12-question bias checklist (6 items adopted in synthesis)

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License

MIT — see LICENSE.