Pre mortem

Skill chrisdavidson/first-principles-skill/first-principles/skills/pre-mortem

Claude Code plugin for systematic first-principles thinking — a 5-phase methodology (identify essence, challenge assumptions, establish ground truths, reason upward, validate) plus 13 companion skills. Installable via the Claude Code plugin marketplace; every conclusion traces back to a verified ground truth, not to analogy or convention.

Install

npx -y skills add chrisdavidson/first-principles-skill --skill pre-mortem

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Runs a focused pre-mortem only — prospective-hindsight failure analysis. Invoke via /pre-mortem only.

The file declares its own license as MIT. That is the author’s claim about this one file, and it is not the same thing as the license GitHub reports for the repository, which is listed with the other numbers below.

SKILL.md

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Focused Pre-Mortem Mode

You are running in focused-pre-mortem mode. Execute only the procedure below and produce only its canonical output sections — do not run the full 5-phase first-principles analysis. Skip Step 0 technique selection; the user has already chosen this technique by invoking the slash command directly.

When to reach for this

Use a pre-mortem once a plan has enough specificity to reason about particular failure modes, but before it is finalised and carries organizational momentum. Not the right tool for evaluating options (use trade-off analysis) or for tracing something that already went wrong (use 5-Whys).

Framing

Before any other step, adopt this premise explicitly:

It is approximately six months from now. This plan has failed — not merely underperformed, but failed badly. That outcome is a fact. Working backward: what caused it?

This past-tense framing is not rhetorical. It bypasses the optimism bias that makes forward-looking risk lists generic. Do not skip it or soften it to "might fail" — the grammatical shift from possibility to accomplished fact is the mechanism.

Procedure

Restate the premise. Before writing anything, say or write: "The plan has already failed. What caused it?" This re-anchors the prospective-hindsight frame before analysis begins.
Write independently. List every cause of the failure without filtering — write the full list before reviewing it. Do not discard causes that seem unlikely; the list is raw material, not a verdict.
Interrogate the list adversarially. Re-read each item and ask: "Would I have suppressed this in a group?" Items flagged by that question are often the highest-signal findings.
Identify recurring patterns. Look for failure causes that cluster — the same root (over-optimistic timeline, single point of dependency, assumption never validated). A cluster is a structural weakness in the plan, not an isolated risk.
Act on findings. Modify the plan to address the structural weaknesses, or explicitly accept the risk with a named mitigation. A pre-mortem with no downstream plan change was box-ticking.

Example

Plan: Host a dinner party for twelve people in two weeks, cooking a full three-course meal from scratch for the first time at this scale.

Framing applied: It is two weeks from now. The dinner party has failed badly. What caused it?

Backward-derived failure causes:

Underestimated preparation time; last two courses were served an hour late
A key ingredient unavailable the day before; no substitution plan
One course required equipment not owned and not sourced in advance
Two guests had dietary restrictions not asked about until the day of
Energy depleted by the time guests arrived; host unable to enjoy the evening

Pattern identified: Every cause traces back to a single structural weakness — no dry run at smaller scale and no contingency check before commitment. The plan assumed novelty would resolve itself on the day.

Failure modes

Forward-looking framing. "What could go wrong?" produces a generic risk list. If causes feel speculative and mild, the past-tense premise was not adopted.

Running it too early. A pre-mortem on a plan with insufficient specificity yields generic concerns. The plan must have enough detail to reason about particular failure modes — vague plans produce vague analyses.

Anchoring (in group settings). When facilitated, the most senior voice in the room shapes the list. Run independent writing before any sharing — each participant writes silently before the group compares lists.

First-speaker anchoring. The first cause named draws subsequent thinking toward it. Write exhaustively before ranking or grouping.

No follow-through. A pre-mortem with no downstream plan change was box-ticking. Findings must modify the plan or be explicitly accepted with named mitigations.

Handoff

The probable failure causes identified here feed Phase 5 (Validate). Add the highest-signal structural weaknesses to the adversarial validation pass — each one is a weak-link candidate for the signed-off analysis to address or explicitly accept.

If a fuller analysis is needed afterward, invoke the main first-principles agent with this output as Known ground truths.