Agent skill

Pre Mortem

by avelikiy in avelikiy/great_cto

Imagine the project has already shipped and failed catastrophically — work backwards from the failure to identify the most likely causes BEFORE building.

MITAuto-check passedDevOps & Cloud

Install Pre Mortem

skills CLI
$ npx skills add avelikiy/great_cto --skill pre-mortem -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install avelikiy/great_cto pre-mortem --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/avelikiy/great_cto.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/pre-mortem .claude/skills/pre-mortem && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
pre-mortem
GitHub stars
103
Token cost
~1.6k tokens
SKILL.md length
661 words
Files
1
Skills in repo
27
Repo updated
First seen
Licence
MIT

At a glance

Imagine the project has already shipped and failed catastrophically — work backwards from the failure to identify the most likely causes BEFORE building.

  • Works in 5 steps: Imagine you're 6 months in the future → Write the post-mortem newspaper headline → List every individual reason this exact… → …
  • DevOps & Cloud work in your project
  • SKILL.md covers The 5-step pre-mortem, Template — add to PLAN-*.md, Common failure modes by… and Anti-patterns in pre-mortems, plus 1 more section
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Pre Mortem is an agent skill from avelikiy/great_cto. Imagine the project has already shipped and failed catastrophically — work backwards from the failure to identify the most likely causes BEFORE building. Forces concrete risk identification, not vague "what could go wrong" lists.

Its SKILL.md is about 1.6k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in DevOps & Cloud. The repository describes itself as: You already have the agent. This is everything around it. greatcto runs Claude Code as a pipeline of 70 specialist agents — an independent model checks each stage before the next… The licence is MIT.

When your agent uses it

  • DevOps & Cloud work in your project

Example prompts

  • “what could go wrong”
  • “/pre-mortem”

Requirements

  • Pre-approved tools (allowed-tools): Read, Write

Workflow steps

5 steps, taken from the step headings in SKILL.md.

  1. Imagine you're 6 months in the future
  2. Write the post-mortem newspaper headline
  3. List every individual reason this exact failure happened
  4. Rank by likelihood × severity
  5. For each top-3 cause, write a guardrail in the plan

What it can do on your machine

Read from SKILL.md and the folder at commit 5d6e760. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves these tools, so the agent can use them without asking each time:

    • Read
    • Write

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md (its code samples are markdown).

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Pre Mortem loads about 1.6k tokens when it runs. Until then it costs about 60 tokens; SKILL.md has 661 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~60
When it runs · the whole SKILL.md, loaded when a task matches
~1.6k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from avelikiy/great_cto at commit 5d6e760, republished under its MIT licence (© avelikiy). 661 words, ~1,645 tokens.

Download SKILL.mdSave it as .claude/skills/pre-mortem/SKILL.md (or your agent's skills folder).
name
pre-mortem
description
Imagine the project has already shipped and failed catastrophically — work backwards from the failure to identify the most likely causes BEFORE building. Forces concrete risk identification, not vague "what could go wrong" lists.
allowed-tools
Read, Write
when_to_use
Apply BEFORE implementation begins: - architect, after writing ARCH but before gate:plan - pm, while breaking work into tasks (Pre-mortem section in…
effort
medium
paths
docs/plans/**, docs/architecture/**, docs/threat-models/**

Pre-mortem — fail-it-before-you-build-it

A retrospective for a project that hasn't happened yet. Surfaces real risks that "list every risk" prompts miss.

Originated in Gary Klein's research at MIT Sloan, now standard at AWS and other ops-mature orgs.

The 5-step pre-mortem

Step 1. Imagine you're 6 months in the future

The project shipped. It is a clear, public failure. There's a Reddit thread about it. The CEO is asking what went wrong.

Step 2. Write the post-mortem newspaper headline

One sentence. Concrete. Specific. Examples:

  • ❌ Bad: "We had some quality issues."
  • ✅ Good: "On 2026-09-12, the Stripe webhook handler deduplicated by raw body hash, so 30K customers were double-charged after Stripe retried delivery during a network blip."

The headline forces you to name the failure mode SPECIFICALLY.

Step 3. List every individual reason this exact failure happened

Brainstorm 10-15 reasons. Be specific. Each item should reference:

  • A real component / file
  • A real failure mode (race condition, schema mismatch, expired credential)
  • A real human factor (oncall didn't see alert, runbook was outdated)

Reject hand-waves like "testing was insufficient." Replace with "we didn't write a property-based test for the dedup-key collision case."

Step 4. Rank by likelihood × severity

For each cause, score:

  • Likelihood: 1-5 (1=once-in-a-decade, 5=monthly)
  • Severity: 1-5 (1=cosmetic, 5=data loss / regulatory breach)
  • Risk score: likelihood × severity

Top 3 by risk score → these are your highest-priority mitigations.

Step 4b. Classify risks — Tigers / Paper Tigers / Elephants

After scoring, classify each risk into one of three types:

🐯 Tigers — Real problems you personally believe could derail the project

  • Based on evidence, past experience, or clear logic
  • Should keep you awake at night
  • Require concrete action
  • Classify each Tiger by urgency:
    • Launch-Blocking: Must be resolved before shipping (broken core feature, regulatory blocker, data integrity risk)
    • Fast-Follow: Must be resolved within 30 days post-launch (performance issues, secondary features)
    • Track: Monitor post-launch, fix if it becomes an issue (edge cases, nice-to-haves)

📄 Paper Tigers — Concerns others might raise that you don't believe are real risks

  • Valid-sounding on the surface but unlikely or overblown
  • Not worth significant resource investment
  • Worth documenting to align stakeholders and avoid repeated debates
  • For each: explain WHY you don't believe it's a real risk

🐘 Elephants — Things the team knows about but isn't discussing openly

  • Uncomfortable concerns: technical debt, team tension, unrealistic timeline, design that nobody likes
  • Uncertain — you're not sure if it's a problem, but nobody is investigating
  • Deserve explicit surfacing before launch — silent elephants become Tigers post-launch
Show full SKILL.md (262 more words)Show less
Step 5. For each top-3 cause, write a guardrail in the plan

Each guardrail is a concrete change to the plan:

  • A test that would have caught it
  • A circuit breaker / feature flag
  • A runbook entry
  • A monitoring alert with specific SLO

If a top-3 cause CANNOT be mitigated within the time/budget, escalate to the user: "This plan accepts the risk of X with no mitigation."

Template — add to PLAN-*.md

markdown
## Pre-mortem

Six months from now, this project failed. Headline:

> <one-sentence failure headline>

### Top reasons (likelihood × severity)

| Cause | L | S | Risk | Mitigation in plan |
|---|---|---|---|---|
| <specific cause> | 4 | 5 | 20 | <Task #N: write idempotency test> |
| ... | | | | |

### 🐯 Tigers (real risks — require action)

| Tiger | Classification | Mitigation | Owner | Due |
|-------|---------------|-----------|-------|-----|
| <risk> | Launch-Blocking | <concrete action> | <team/person> | <date> |
| <risk> | Fast-Follow | <concrete action> | <team/person> | <date> |
| <risk> | Track | <monitoring approach> | <owner> | post-launch |

### 📄 Paper Tigers (overblown — document to align stakeholders)

- **<concern>**: Not a real risk because <reason>. If <condition> changes, revisit.

### 🐘 Elephants (unspoken — needs open discussion)

- **<concern>**: Nobody is talking about this. Suggested conversation: "<how to raise it>".

### Accepted risks (no mitigation)

- <risk> — accepted because <budget/scope reason>. Owner: <name>.

Common failure modes by archetype

Quick start — most-common pre-mortem causes per archetype:

ArchetypeCommon failure
fintech / commerceIdempotency-key collision; double-charge during retry storm
healthcarePHI leak via debug log; BAA not signed with vendor
web3Oracle staleness; flash-loan exploit on bonding curve
mlopsTraining/serving skew; model drift undetected
iot-embeddedOTA bricks devices in a region with no recovery path
data-platformLate-arriving data overwrites correct values
ai-system / agent-productPrompt injection exfiltrates other users' data
enterprise-saasCross-tenant data leak via RLS gap
cli-toolDestructive flag with no confirmation (rm -rf equivalent)
libraryBreaking change in minor version bump

Anti-patterns in pre-mortems

❌ Vague risks. "Performance might be a problem." Be specific: which operation, at what load, what's the SLO.

❌ Cosmic risks. "AWS could go down." Yes, but that's not actionable. Focus on what you can mitigate.

❌ Defensive list. Listing risks you've already mitigated to look thorough. Only list risks the current plan does NOT yet address.

❌ Skip the headline. Without the headline, the team won't believe the failure scenario is real.

When to skip

  • nano project_size — pre-mortem is overhead.
  • Pure refactor with full test coverage — guardrails already exist.
  • Bug-fix with one-line repro — risk is well-bounded.

© avelikiy, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in skills/pre-mortem of avelikiy/great_cto.

Open the folder on GitHubat commit 5d6e760

Compare with similar skills

Pre Mortem next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Pre Mortem compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Pre Mortem this skillavelikiy/great_cto103—~1.6kAutomated safety check: PassMIT
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Terraform and OpenTofu Guideagentscope-ai/QwenPaw36k6 repos~4.2kAutomated safety check: PassApache-2.0
Vercel Optimize Auditvercel-labs/agent-skills32k8 repos~4.3kAutomated safety check: PassNone
Analyze GitHub Action Logswithastro/astro63k1 repos~1.3kAutomated safety check: PassCustom licence
Openclaw Live Updateropenclaw/openclaw392k—~3.7kAutomated safety check: PassMIT

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Categories

Questions about Pre Mortem

What does Pre Mortem do?

Imagine the project has already shipped and failed catastrophically — work backwards from the failure to identify the most likely causes BEFORE building. Pre Mortem is an agent skill from avelikiy/great_cto. Imagine the project has already shipped and failed catastrophically — work backwards from the failure to identify the most likely causes BEFORE building.

When should I use Pre Mortem?

Pre Mortem fits situations like: devOps & Cloud work in your project.

How do I install Pre Mortem in Claude Code?

Run `npx skills add avelikiy/great_cto --skill pre-mortem -a claude-code`. Or copy the skill folder (skills/pre-mortem in avelikiy/great_cto) into .claude/skills/pre-mortem in your project. Claude Code loads it when a task matches its description.

How do I install Pre Mortem in Codex?

Run `npx skills add avelikiy/great_cto --skill pre-mortem -a codex`. Or copy the skill folder (skills/pre-mortem in avelikiy/great_cto) into .agents/skills/pre-mortem in your project. Codex loads it when a task matches its description.

Can I use Pre Mortem in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add avelikiy/great_cto --skill pre-mortem -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/pre-mortem, .gemini/skills/pre-mortem, .github/skills/pre-mortem and .opencode/skills/pre-mortem in your project.

What does Pre Mortem need to run?

SKILL.md names no scripts, command-line tools or credentials: Pre Mortem is instructions for the agent only. Its frontmatter pre-approves these tools: Read, Write.

Does Pre Mortem access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Pre Mortem safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Pre Mortem use?

Pre Mortem is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Pre Mortem use?

About 1.6k tokens (SKILL.md is roughly 6.6k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Pre Mortem?

Skills that share tags, products or a category with Pre Mortem: Monitor CI (nrwl/nx, 29k stars), Terraform and OpenTofu Guide (agentscope-ai/QwenPaw, 36k stars), Vercel Optimize Audit (vercel-labs/agent-skills, 32k stars) and Analyze GitHub Action Logs (withastro/astro, 63k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Pre Mortem?

avelikiy (a GitHub user) maintains it in avelikiy/great_cto, which has 103 GitHub stars. The repository holds 27 skills in this directory. The repository was last updated on October 9, 2026.

Source: avelikiy/great_cto on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.