Design your validation gates

What you will learn Not a chapter to read but one to do. Take one of your own outputs and write the conditions under which it could ship without a human looking. Whatever you cannot write down is exactly why a human is still attached.

What you need

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□ 40 minutes□ One output that actually goes outside   · a code deploy, a document that reaches a customer, an external post□ One person who reviews it today□ Paper or a spreadsheet

Step 1 — Who looks at what today (10 min)

Write down everything the reviewer actually checks with their eyes. Including "skims it."

#	What they check	Why	How long
1
2
3

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How to write it:  "checks the quality" ✗   -> write what tells them the quality is bad  "checks the numbers add up" ✓  "checks it sounds like us" ✓

Mark any row whose "why" is blank. It may be the scar of an old incident, or it may be habit nobody can account for.

Step 2 — Sort into three (10 min)

Sort each row by who can decide it.

Class	Test	Examples
A machine decides	the answer is true or false	totals, required fields, format, dead links
A machine flags	it can raise a suspicion	odd tone, unusual values, banned words
Only a person	needs context and accountability	is this the right thing to say right now

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□ Every row from step 1 is in one of the three□ If "only a person" is more than half -> do step 2 again

That second line is the common outcome. On the first pass, almost everything lands in "only a person." Split them once more — "is this document right" needs a person, but "does the amount match the table" inside it does not.

Step 3 — Stand up three gates (15 min)

Lay them out in the order from automatic validation.

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Gate 1 (machine, seconds)  : fails -> nothing proceeds at allGate 2 (machine, minutes)  : fails -> flagged for a personGate 3 (person, as needed) : only what gate 2 flagged

Gate	What it checks	On failure
1
2
3

What every gate must state

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□ Is the pass condition written in one line?□ What happens on failure (halt? flag? roll back?)□ Who gets told

Without the second, it is not a gate — it is a log. If failing changes nothing, nobody reads it.

Step 4 — Check the way back (5 min)

One last question.

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□ If it passed every gate and still went out wrong, how long to undo it?

Answer	What it means
Minutes	you can afford loose gates. Ship fast and fix
Hours	the design above is about right
It cannot be undone	gate 3 with a person is mandatory

The cost of undoing sets the thickness of the gates. Thick gates on cheap-to-undo work only cost you speed; thin gates on irreversible work produce an incident eventually.

Self-check

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□ You wrote what the reviewer checks, with the reason□ "Only a person" came down to half or less□ Every gate says what happens on failure□ You actually answered the time-to-undo question

If the second failed, go back to step 2 and split further. A lot of "only a person" does not mean validation is hard — it means you have not split it yet.

Check yourself

1. What do you do when "only a person" is more than half the rows?

Answer

Split the rows further. "Is the document right" needs a person, but "does the amount match the table" inside it does not. Left whole, all of it stays with the human.

2. What happens if a gate does not say what failure does?

Answer

It becomes a log, not a gate. If failing changes nothing, nobody looks at it, and you end up with checks that run and no control.

3. What sets the thickness of a gate?

Answer

The cost of undoing. If it can be undone in minutes, loosen the gates and ship faster. If it cannot be undone, a human gate is mandatory.

Pass validation and it ships → Process 4 — immediate delivery