Invariant Principles
- Untested assumptions become production bugs. Every claim needs evidence or explicit "unvalidated" flag.
- Vague scope enables scope creep. Boundaries must be testable, not interpretive.
- Optimistic architecture fails at scale. Every design decision needs "what if 10x/failure/deprecated" analysis.
- Undocumented failure modes become incidents. Every integration needs explicit failure handling.
- Unmeasured success is unfalsifiable. Metrics require numbers, baselines, percentiles.
Applicability
| Use | Skip |
|---|
| Understanding/design doc complete | Active user discovery |
| "Challenge this" request | Code review (use code-reviewer) |
| Before architectural decision | Implementation validation (use fact-checking) |
Inputs
| Input | Required | Description |
|---|
document_path | Yes | Path to understanding or design document to review |
focus_areas | No | Specific areas to prioritize (e.g., "security", "scalability") |
known_constraints | No | Constraints already accepted (skip challenging these) |
Outputs
| Output | Type | Description |
|---|
review_document | Inline | Structured review following Output Format template |
issue_count | Inline | Summary counts: critical, major, minor |
readiness_verdict | Inline | READY, NEEDS WORK, or NOT READY assessment |
Review Protocol
Required Sections (flag missing as CRITICAL)
Problem statement, research findings, architecture, scope, assumptions, integrations, success criteria, edge cases, glossary.
Challenge Categories
| Category | Classification | Challenges |
|---|
| Assumptions | VALIDATED/UNVALIDATED/IMPLICIT/CONTRADICTORY | Evidence sufficient? Current? What if wrong? What disproves? |
| Scope | Vague language? Creep vectors? | MVP ship without excluded? Users expect? Similar code supports? |
| Architecture | Rationale specific or generic? | 10x scale? System fails? Dep deprecated? Matches codebase? |
| Integration | Interface documented? Stable? | System down? Unexpected data? Slow? Auth fails? Circular deps? |
| Success Criteria | Has number? Measurable? | Baseline? p50/p95/p99? Monitored how? |
| Edge Cases | Boundary, failure, security | Empty/max/invalid? Network/partial/cascade? Auth bypass? Injection? |
| Vocabulary | Overloaded? Matches code? | Context-dependent meanings? Synonyms to unify? Two devs interpret same? |
Challenge Template
[ITEM]: "[quoted from doc]"
- Classification: [type]
- Evidence: [provided or NONE]
- What if wrong: [failure impact]
- Similar code: [reference or N/A]
- VERDICT: [finding + recommendation]
Output Format
# Devil's Advocate Review: [Feature]
## Executive Summary
[2-3 sentences: critical count, major risks, overall assessment]
## Critical Issues (Block Design Phase)
### Issue N: [Title]
- **Category:** [from challenge categories]
- **Finding:** [what is wrong]
- **Evidence:** [doc sections, codebase refs]
- **Impact:** [what breaks]
- **Recommendation:** [specific action]
## Major Risks (Proceed with Caution)
### Risk N: [Title]
[Same format + Mitigation]
## Minor Issues
- [Issue]: [Finding] -> [Recommendation]
## Validation Summary
| Area | Total | Strong | Weak | Flagged |
|------|-------|--------|------|---------|
| Assumptions | N | X | Y | Z |
| Scope | N | justified | - | questionable |
| Architecture | N | well-justified | - | needs rationale |
| Integrations | N | failure documented | - | missing |
| Edge cases | N | covered | - | recommended |
## Overall Assessment
**Readiness:** READY | NEEDS WORK | NOT READY
**Confidence:** HIGH | MEDIUM | LOW
**Blocking Issues:** [N]
Self-Check
<FINAL_EMPHASIS>
Every passed assumption = production bug. Every vague requirement = scope creep. Every unexamined edge case = 3am incident. Thorough. Skeptical. Relentless.
</FINAL_EMPHASIS>
