✓ Free · MIT License Manufacturing Healthcare Quality

Mistake-Proofing (Poka-Yoke)

The goal isn't to find errors faster. It's to make errors impossible. Poka-yoke is how. Analyzes every error opportunity in a process and generates solutions ranked from strongest (elimination) to weakest (procedure).

⬇ Download Skill The hierarchy ↓

Problems This Solves

Three signs a process is relying on the wrong controls

Inspection catches errors after they occur

Every defect that inspection catches is a defect that the process already made. Inspection is not quality. It's damage control after quality failed.

"Retrain" is the corrective action for recurring defects

If an error has happened more than once, retraining is not a corrective action. It's a hope. The process made the error easy; the solution is to make the error hard or impossible.

Teams don't know detection from prevention

A sensor that stops a machine when a part is missing is detection. A fixture that makes it impossible to load a part the wrong way is prevention. They are not equivalent, and the hierarchy below explains why.

The Hierarchy

Five levels, strongest to weakest

The hierarchy forces a discipline: before you reach for a sensor or an inspection step, prove you've considered whether the step can be eliminated or made physically impossible to get wrong. These five levels are this toolkit's own ranking, not a Shingo standard. Shigeo Shingo, who developed poka-yoke within the Toyota Production System, sorted devices into control types that stop the process and warning types that signal a problem, and by method: contact, fixed-value or motion-step.

Elimination

Remove the process step entirely. The error opportunity disappears with it. The strongest solution because it requires no control at all.

Prevention

Make the error physically impossible. Asymmetric connectors, keyed fixtures, and counting dispensers prevent the wrong action from occurring, not catching it after.

Detection

Catch the error immediately, before the work moves to the next step or the next operator: sensors, gauges, go/no-go checks. The error still occurs, but it's caught at the point of occurrence rather than downstream.

Mitigation

Reduce the impact when an error gets through. Fuses, overflow drains, auto-shutoffs. Weak: the error still happens, but the consequence is smaller.

Procedure

A written step, reminder or checklist added to the process. It relies entirely on people complying and paying attention, so it is the weakest level and the skill does not call it mistake-proofing.

Retrain is not poka-yoke

Human-dependent controls like training, checklists, and reminders sit at Level 5, the weakest rung, because they depend on every person being correct every time. The skill will generate human-dependent solutions when nothing else is feasible, but it labels them explicitly as the weakest level and asks whether a stronger solution exists.

Error Type Taxonomy

Six types of errors, six solution directions

Before generating solutions, the skill classifies each error opportunity by type. Different error types require different poka-yoke approaches. An omission and a quantity error need completely different solutions even when they occur in the same process step.

Type 1

Wrong item

Wrong part used, similar-looking items confused, wrong patient ID entered

Type 2

Omission

Fastener not installed, step skipped, field left blank

Type 3

Sequence error

Process steps performed in the wrong order, assembly reversed

Type 4

Timing error

Action performed too early, too late, or for the wrong duration

Type 5

Quantity error

Too many or too few fasteners, incorrect dose volume

Type 6

Extra action

A step repeated, or a component added that should not be

Solution Examples

Concrete solutions for each error type

The skill maps each error type to a set of known poka-yoke starting points, then ranks the solutions by hierarchy level and feasibility for the specific process.

Wrong item

Shape differentiation (keying)

Parts that only fit where they belong. Pair it with separate storage locations and color-coding at the point of use, so the wrong item is hard to pick in the first place.

Omission

Presence sensor

Verifies completion before the process is allowed to advance. A fixture that cannot be closed until every component is loaded works the same way.

Sequence error

Physical interlock

Step B cannot begin until Step A is confirmed. Single-piece flow and labeled staging locations also make out-of-sequence work visible immediately.

Timing error

Timer with alarm or lock

A timer built into the fixture with an audible or visual alarm, or a lock that cannot be opened until the timer expires.

Quantity error

Pre-counted kit or fixed-slot tray

The correct quantity is in place before the operator starts: pre-counted kits, pre-measured doses, trays with fixed quantity slots.

Extra action

Already-done indicator

A status indicator that shows the step is complete (a filled light, a turned indicator, a locked position), or a fixture that physically blocks a second operation.

Examples

Manufacturing and clinical applications

🏭 Manufacturing

🏥 Healthcare

Circuit board assembly: 3 error opportunities identified (wrong component, missing component, wrong quantity of solder paste). Ranked solutions generated for each: keyed feeder slots for the wrong component, a pre-measured dispenser for the paste quantity, and a vision check after placement for the missing component.

Process: PCB Assembly — Component Placement
Error opportunities identified: 3
Error types: Wrong item · Omission · Quantity error

Solution ranking:
1. Keyed feeder slots so only the right reel fits (Level 2, prevention)
2. Pre-measured solder paste dispenser (Level 2, prevention)
3. Vision system check after placement (Level 3, detection)
[NEEDS GEMBA: confirm the existing feeders can take a keying feature]

Medication administration in a hospital unit. The skill adapts vocabulary to clinical context: "operator" becomes "nurse," "part" becomes "medication." Unit-dose packaging and barcode verification at the bedside map to Levels 2 and 3. Tall-man lettering is a visual alert that depends on a person noticing it, so it sits at Level 5.

Healthcare note

The right-patient, right-drug, right-dose checks are Level 3 (detection) controls at best when implemented as manual verification. The skill flags opportunities to move toward Level 2–3: barcode scanning with forced workflow, unit-dose packaging, and smart pump libraries that block out-of-range entries.

What you get

A real run on the sample data

Unedited output. The sample message at the top went to Claude Sonnet 4.6 (an earlier-generation model, so a newer one may word things differently) with this skill pasted in, the same way the steps below show, on September 29, 2026. Scroll inside the frame to read the whole reply.

Open the full image

Installation

Describe the process. Get the solutions.

Copy the skill. Open mistake-proofing.md, select all the text and copy it.

Paste it into Claude. In claude.ai, start a new chat and paste it as your first message, or paste it into a Project's instructions so it's there every time. The free plan works, and free accounts can keep up to five Projects.

Say what's in front of you, in your own words: describe the process steps, or paste a process map, SOP, or FMEA (leave out names). Add "just draft it" to skip the questions and get the whole deliverable now.

See a finished example first (optional): the worked examples are in the download, in the resources/examples folder.

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