Learn Fail-closed doctrine: from zero to expert, then sell it

No AI background needed. Five levels, each with something to actually do, at your own pace. Tick items as you go (your ticks stay in this browser).

Evidence, proof and selling tools for Fail-closed doctrine

Level 1 Beginner: understand it

Many security tools have a hidden weakness: when the check itself breaks, they let the action through, because blocking would annoy users. Attackers know this and try to make checks fail.

CAIN-42's rule is the opposite: any enforcing check that errors, times out, answers with a word nobody wrote, or never answers, blocks the action. We tested this by sending 1,440 malformed requests to our routes (0 were allowed, 0 crashed) and found and fixed one real hole.

Think of it like this: A door that locks when the power fails, rather than one that swings open. Hotels choose one; banks choose the other.

Read the full plain-English explanation: Fail-closed doctrine, explained.

• I read the explanation above.
• I can say what it does in one sentence, without notes.

Level 2 User: see it work

Run it live: open the live demo. Before each result, guess what will happen. These are checks it must pass:

• Honest read, brand-new agent: A reasonable action from a principal with no trust history. Unknown trust is held for a human, not allowed.
• Prompt injection in the payload: The risk stage screens every nested key and value; a hit on an enforcing stage blocks.
• Malformed plan: A plan the checker cannot read is an unanswered check, and an unanswered enforcing check blocks.
• Mission escalation: A tool outside the declared mission is refused even though the caller is authenticated.
• Consequence horizon exhausted: The uncertainty budget for this agent is spent; more autonomy is not granted on credit.
• Governance program needs re-authorization: A signed policy program that does not re-execute to ALLOW for exactly this call refuses it.

• I ran the live demo.
• I can explain what one of these checks shows.

Level 3 Verifier: prove it yourself

This is the skill that sets you apart: you don't have to believe us, and neither do your customers.

1. Install Python 3 if you don't have it (python.org/downloads).
2. Download the kit and unzip it.
3. Open a terminal in that folder. On Windows, click the folder's address bar, type cmd and press Enter. On a Mac, right-click the folder and choose New Terminal at Folder.
4. Run python3 verify.py (on Windows, python verify.py). It checks the seal without the internet.
5. Run python3 verify.py --live. It repeats every check from your own computer.
6. Try to cheat it: open transcript.json in a text editor, change one character, save, and run python3 verify.py again. It must now say FAIL. Unzip a fresh copy afterward.

• I ran the kit's check on my own computer.
• I changed a file and saw it fail.

Level 4 Expert: know the edges

An expert knows what a product does not do, and says it first. That is what makes a buyer trust you.

Read its limits page in full: what Fail-closed doctrine does not do.

You can say

• Errors, timeouts and unknown answers block.
• 1,440 malformed requests: 0 allowed, 0 crashes.

Never say

• "It can never fail open": shadow mode reports degraded states by design.
• "The latest fix is live" (until deployed).

Read the questions real buyers send, with honest answers: answers to buyer questions.

Test yourself (click a question to see the answer)

• I got every quiz question right without looking.
• I can name one thing it does not do.
• I explained it to a friend, and they understood it.

Want a formal study path? The CAIN Academy has courses and exams. Finishing this page is your own practice; it is not a qualification or certification.

Level 5 Seller: put it in front of a customer

1. Copy, paste, send: the shortest route, no technical skill needed.
2. Who buys it and where to find them.
3. The sales conversation, then the offer and the close.
4. The rules: read these before your first message.
5. Selling tools with this product's evidence built in: pitch, emails, call script, objection answers, one-pager.

• I read the rules.
• I sent my first personal message.

About money: your share is agreed in writing with FIRME AI CORPORATION before your first message (email vincent@firmeai.com). Nothing here promises income. Most messages get no reply; that is normal.