Adversarial Gate

Coined by Jaroslav Pantsjoha (#HarnessEngineering). The Adversarial Gate is the practice of forcing an agent — or a human — to argue against their own design before proceeding. It pre-empts bad reasoning before bad output exists.

The gate has one question: "How would I break this?"

Answer it honestly. If you cannot name at least two plausible failure modes, you do not understand the system well enough to ship it.

When to use

• Before finalising any architecture or design decision
• Before a deployment or release
• When an agent is about to take an irreversible action
• When a design looks clean and elegant (danger signal — simple-looking systems hide the hard failure modes)
• When the team is under time pressure and "just shipping it" feels compelling

Procedure

1. State the proposal clearly — in one or two sentences, what is the approach being validated?
2. Run the adversarial pass — argue against it. Ask:
   • What is the single most likely way this fails in production?
   • What happens under load / at scale / with bad input?
   • What is the blast radius if this fails? Is it recoverable?
   • What assumption does this design make that could be wrong?
   • What does the monitoring not cover that would let this fail silently?
3. Name at least two concrete failure modes — not "something could go wrong" but specific, nameable failures.
4. Check each failure mode has a mitigation or an accepted risk owner — unmitigated = not shippable.
5. Document the outcome — pass (risks named and owned) or fail (proceed to redesign). Attach to the ADR or PR.

Outputs

• Adversarial Gate verdict: PASS / FAIL
• Named failure modes with mitigations or risk-owner sign-off
• Optional: a short paragraph appended to the ADR or PR description summarising the gate result

Guardrails

• One argument is not enough. A single failure mode is the one you were already thinking about. The Adversarial Gate is looking for the one you were not.
• "We have tests" is not a mitigation. Tests cover known paths. The gate is looking for unknown paths.
• Time pressure does not suspend the gate. Pressure is when you need it most.
• The gate is not pessimism. It is the fastest route to confidence — because you have already stress-tested the design yourself.

Anti-rationalization table

Excuse the agent makes	Counter
"This is a low-risk change"	All production incidents started as low-risk changes. Name the failure mode or accept you cannot assess risk.
"We can fix it after if something breaks"	Blast radius unknown = not low risk. Run the gate.
"The tests cover this"	Tests cover happy paths. The gate looks for the paths tests miss.
"We've done this before"	Prior success is not a guarantee. Conditions change. Run the gate.
"The deadline is today"	A production incident will cost more time than the gate. Run the gate.
"I'm confident in this design"	Confidence is the leading indicator of skipped gates. Run it anyway.

Reference

This pattern converges with “doubt-driven development” in Addy Osmani's agent-skills. The Adversarial Gate name and “how would I break this?” framing are JP's #HarnessEngineering contribution. The anti-rationalisation table format was adopted after reviewing that MIT-licensed project; this repository does not claim the table format originated here.