The Viability Sprint, explained.
Related: Concept validation · Idea screening · Stage-gate concept review
A structured way to know if your product idea is worth building, before you spend money on it.
Five questions test four dimensions: market, value, cost, feasibility. Out comes a Specification and a Viability Report telling you to build, refine, or shelve. Two hours with pen and paper, or fifteen minutes through the guided GPT. Walkthrough at the bottom.
What is a viability sprint?
A structured interview run against a product idea before any money goes into building it. Five fixed questions. Two short documents fall out the other end:
- Specification: the idea, structured. What it is, who it’s for, what it costs to make.
- Viability Report: the directional read. Strengths, risks, recommended next step.
The questions test four dimensions: market, value, cost, feasibility. Get those four hanging together and you’ve got a buildable product. Where they don’t hang together, you’ve just saved yourself months. Cheaper to find that out now.
When to use one
- You have a physical product idea you haven’t built yet.
- You’re deciding whether to commit real money or time to it.
- You need a defensible answer to share with co-founders, investors, or yourself.
When to skip it
- You’ve already validated demand. Skip ahead to Discover or Define.
- You’ve built a prototype customers used. Go to user testing.
- It’s a software-only product. Lean Startup MVP loops fit better.
The five questions
These are the five. Each takes 15 to 30 minutes if you’re being honest with your idea, longer if you’re not. Between them, all four viability dimensions get tested.
Who has this problem? Be specific. Most founders open with something far too broad: “people who like baking”, “busy professionals”. A target market that wide doesn’t tell you what to build. A real persona has a particular kind of person, in a particular situation, with a particular constraint that shapes what they need. If your answer fits onto a Tesco demographic chart, it’s not narrow enough.
How painful is it? Two things matter: how often the pain hits, and how badly it hurts when it does. Plot them on a quick 2×2. Viable products live top-right: frequent, moderately painful. Daily annoyances carry products; the rare crisis almost never does, no matter how acute.
What do they do about it now? Of the five, this is the question I lean on hardest. The answer tells you the budget you’re really competing for. If they’re doing nothing, the pain isn’t real enough to part with money for it. If they have a workaround, the cost of that workaround is your price ceiling.
What would solving it be worth? Willingness-to-pay, anchored against the cost of the current workaround. Test several price points. Watch where the answers swing from no to yes. Cheap, annoying workarounds suggest a low ceiling. Workarounds that hide costs push the ceiling higher than it looks. The hidden costs are usually time wasted, mental load, or the embarrassment of asking for help. None of those show up on the receipt, but they’re what makes someone pay £149 for a box that just holds the temperature, when in theory they could keep fighting the oven light and a thermometer for nothing.
What would it take to build? This is where the engineering question comes in. Rough out a bill of materials. Pick a likely manufacturing route. List the certifications you’d need (UKCA at minimum, if it plugs into a wall). That gives you an order-of-magnitude cost floor. If the floor sits above the ceiling from Q4, the product can’t work as conceived. The whole point of running the sprint is finding that out in an afternoon, not after a year of CAD work.
Run against the proofing box, the five questions landed like this. One page, four dimensions, a clear read.
Pick a product idea you’ve been thinking about. Read each question, write your answer, then keep reading. The article works better if you have your own answers in front of you.
How it fits the bigger picture
The Innovate Engineer process splits product development into ten stages. The first five are about designing the right thing. The last five are about designing the thing right. A viability sprint is a fast pass through the first five. Enough to know whether the idea makes sense; nowhere near enough to build it.
What it can do
It tells you whether the broad shape of the idea hangs together.
What it can’t do
It can’t tell you whether a specific customer will buy. That’s Stage 02 work. It also won’t tell you whether a feature is technically optimal. Stage 07 lives there.
See the full 10-stage process →
Try it yourself
The five questions are above. Pen and paper still works. Set aside two hours. Be honest with yourself, especially on Q1, and write the two short documents at the end.
Or skip the writing and run the guided version. Same five questions scripted into a free AI interview, with a Specification and Viability Report on the way out in fifteen minutes or so. Start the Free Sprint →
Your viability-sprint checklist
Project notes: the proofing-box sprint
▸ From the notebook · optional reading
How a £249 app-connected proofing cabinet became the £149 no-app box in two hours of structured questioning.
4 min read · click to open
Dan and Anna Hartley came to us last winter with an idea for a connected sourdough proofing cabinet. App control, Wi-Fi, three temperature zones, a companion recipe library. They wanted to retail it at £249.
Two hours later the cabinet had become a single heated box, no app, one capacity, at £149. The same problem they walked in with, solved by a simpler product at a fraction of the build cost.
Here’s how those two hours went.
We worked through the five in sequence. Most of two hours. Some answers came in five minutes. Q1 took thirty.
“Anyone who bakes” turned into serious home bakers in cold UK kitchens who proof overnight and cannot hold a steady temperature. Not a beginner, not a professional. Where we landed was someone three or four years in, who cares about the result and resents binning a loaf.
The pain ran high frequency, moderate severity. An overnight prove failing maybe one time in three through a Stockport winter, when the kitchen swings between 14°C and 19°C. Each failure is roughly £4 of flour and twelve hours, plus the quiet sting of caring and still getting it wrong.
The workaround was thin. The oven with the light on (too hot, uneven), a heat mat (no real control), towels round the bowl. No proper fix. Acceptance plus mild resentment, which is the shape pricing questions love. There’s room to charge for relief.
At £249, almost nobody. The app and the three zones were the reason it cost that much, and nobody we spoke to actually wanted them. At £149, the arithmetic worked. Bakers had already spent more than that on flour binned over two winters, and on mixers they used less.
The original concept (app, Wi-Fi, three zones, firmware) carried a bill of materials well into three figures, plus an ongoing support burden. As conceived it sat above the price ceiling. But once the persona was sharper, the smart features turned out to be the problem, not the product. The real job was “hold 26°C overnight so I can stop worrying about it”. A single heated ceramic box with a rotary knob and a small OLED does exactly that, on a £38–55 BOM out of Stoke-on-Trent ceramic and a Manchester PCB.
What changed
- Connected cabinet: app, Wi-Fi, three temperature zones
- Multiple capacities and a recipe library
- Target price £249
- Next-stage cost: a five-figure development programme
- Single heated box, no app, one capacity
- Ceramic shell, rotary knob, small OLED
- Target price £149
- Next-stage cost: a first prototype in the low thousands
None of that surfaced from the original brief. None of it would have come out of build-it-and-see either. The reframing happened in two hours of structured questioning, before any cash was committed. The no-app, single-capacity, £149 box has been the product ever since.
— Next stage → Stage 02 · Discover