A French welder turned site cardboard arithmetic into an app, posted two TikToks a day, and got it into the top 20 French tools chart in five days

Early Nov 4, the TikTok account @welduppocket posted a half-minute job-site video with one line of copy: "WeldUp Pocket, l'application de référence pour les professionnels du métal" (the go-to app for metalworking professionals). Within two days it had 120k views. The comments didn't praise the app. People argued about something more technical: rolling a steel plate into a cylinder, whether you should use a press brake segment by segment or go straight to a four-roll plate roller. The same day, the app's Android installs jumped by 1,200 times in one day, from a previous tens per day. Two days later it reached #20 in the French App Store free chart for tools. The maker is Lison Robin, a certified boiler and pipe welder. This piece explains what the app is, why it took three months to start moving, how it makes money, and who could follow the same path.

What it is: the calculator in a plumber's, welder's or sheet-metal worker's pocket

WeldUp Pocket 的商店描述第一句是「Calculateur de tuyauterie, soudure et chaudronnerie, 100 % hors-ligne」(管道、焊接、钣金计算器,完全离线)。第二段说得更直白:这里收的是管道工、焊工和钣金工「refont de tête ou sur un bout de carton depuis toujours」(一直靠心算或者在一块纸板上算)的东西:斜接弯头(baïonnette)和虾米弯下料、三通的马鞍口(gueule de loup)、钣金展开图、焊机参数怎么调。

In total there are 60+ tools, plus reference material on flange standards, material grades and weld symbols, and it can export pipe layouts to ISO drawings and PDF. The details follow job-site habits: it works without a connection (the description says "under a tank, in a trench, in a ship's hull"), the buttons are big enough to press with gloves on, you can type fractions like "3 1/2", it supports metric and imperial, it organises by job site, and one message sends a whole site's data. No sign-up, no ads.

Robin runs a small welding workshop, WeldUp, in a town in Loire-Atlantique. His site weldup.pro lists 7 ISO 9606 / NR 476 welding certifications and case studies in nuclear, shipbuilding and biomethane piping. This app is the only one under his developer account.

Why it took three months to start moving

The iOS version launched in August 2026 and the Android version in September. By Nov 1 the French store had collected 66 ratings in total, under one a day on average. On Google Play, after mid-October it added only 13 to 17 installs per day (averaged from weekly snapshots). The product was already out and the reviews were fine, but nobody knew it existed.

The turning point came on Oct 30. That day Robin shipped version 1.0 and changed TikTok from one post every few weeks to two posts a day, one around 1 a.m. and one around 9 a.m., with the same copy every time, original audio, and real job-site footage of welds, pipes and tools, overlaid with the app's interface. The numbers that followed (TikTok, as seen by 11-06):

From Nov 1 to 5, the videos add up to about 440k views, and the account reached 11-06 followers at 7,558. Going by the API fields, none of these videos are ads or brand deals. I found no sign of TikTok ad spend, and couldn't check Meta. The same videos also ran on Instagram Reels and YouTube Shorts. No other creator mentions it, no media has covered it, and there's nothing on X. As far as I can tell, the founder's own account drove all of it.

The chart climbs followed the videos: it charted in the France App Store Utilities Top Free chart at #176 on 11-01, then 71, 35, 31,11-06 down to #20, and the same day it hit #151 on the overall France Top Free chart for the first time. Charting countries went from 2 to 18: Belgium, Switzerland, Canada, Mauritius, Senegal, Tunisia, Algeria, Luxembourg and so on, mostly French-speaking places. The French videos reached welders across the whole French-speaking world. On Google Play, 11-04 daily installs jumped from 1,927 to 3,173.

Take it with a grain of salt: the France Utilities Top Free chart has a low bar, and 11-06 only needed 6 new ratings a day worldwide to reach #20. The rank looks big, but the volume is still small. The official site claims "11k monthly active users" and 7,000+ downloads across both platforms, and those two numbers don't match, so don't trust the MAU figure yet.

Why did people watch? Because the videos show work their peers already know. The 120k-view video on 11-04, judging by the comments, is about "croquage" (cutting and rolling steel plate into a cylinder; my guess is the app works out where to make bends on a press brake), and the comments are full of sheet metal workers arguing over three-roll versus four-roll versus press brake, with someone showing off a newly installed plate roller, and others asking "Combien coûte l'application ?" (How much does the app cost?). Its persuasiveness comes from "a real welder using it on a job site," not from editing.

Why users stick around

These calculations are something these workers do every day. Comments from the France App Store:

• "La meilleure appli que j'ai eu la chance d'utiliser pratiquement tous les jours" (The best app I've been lucky enough to use almost every day, 10-07)
• "Sa aide vachement en chantier" (It's a huge help on site, 10-04)
• "J'ai essayé toutes les applications de tuyauterie… de loin la meilleure" (I've tried every pipe app, and this one is by far the best)

iOS 4.9 stars, 18 written reviews, 17 of them five-star. A lot of the reviews are really feature requests, like 11-03 One welder wrote: "Peut être penser à rajouter le temps de refroidissement entre la passe de remplissage et la passe de finition" (could you add a cooling time between the fill pass and the finish pass?). The developer replies to every one, and the site says "chaque suggestion reçoit une réponse" (every suggestion gets a reply).

Where the money comes from

10-30's 1.0 version added a subscription, WeldUp Pro: €4.99/month or €49.99/year, with a one-month free trial on the monthly plan. The everyday calculators stay free with no limits, and "preparation tools and shop documents" go into Pro. On Google Play, in-app purchases show as $3.99–$44.99. Before charging, the team posted a TikTok asking "WeldUp Pocket deviendra-t-elle payante ?" (Will WeldUp Pocket become paid?) to warn people. Even so, 11-03 still brought a three-star review: "L'application et devenue payante je trouve sa un peu dommage" (The app became paid, I find that a bit disappointing).

The second revenue stream is selling to companies: the TikTok bio and the website both say "Offres multi-comptes pro" and "Équiper une équipe" (multi-account business plans, to equip a whole crew), with Robin's personal email as the contact.

No outside data shows paid conversion or revenue. It appeared once on 11-01 at #103 on Belgium's Utilities Top Grossing chart, and it's not on France's Top Grossing chart. For now, the only fair claim is "people want to use it, and it has started making money," not "it's making money."

Who it's competing with

The category is old, but every player is small:

There are dozens of English single-function mini tools, one app per calculation. Nobody has put pipe, welding and sheet metal into one free, French, offline app. The top French apps were two paid tools by Polish developers with 24 ratings combined, and WeldUp passed them in three months. I also haven't seen anyone copy its approach yet.

What you can actually copy

The product isn't hard: 60 tools all rely on public geometry and process formulas, and someone who can code an app could copy the rough version in a few months. What's hard to copy is two other things: the maker is a trade insider, and people in the trade recognize them on TikTok. WeldUp sat for two and a half months with a dozen installs a day, then after switching to two job-site videos a day it charted within five days. The difference wasn't the product, it was distribution. Distribution worked because the person filming was already standing on a job site.

So "copying" comes in three levels of difficulty:

1. Same approach, different trade: electricians, HVAC, plumbing (plomberie), carpentry, roofing, rebar. Whichever trade does its calculations on paper every day is the one to build for.
2. Same trade, different language: WeldUp's interface supports 8 languages (including Arabic and Polish), but its videos and community are French only. Nobody has built content for Spanish, German, Portuguese, Italian or Polish welders and plumbers yet.
3. Fill the gaps it hasn't filled: multi-seat company accounts, crews sharing job-site data, and integration with welding procedure specifications (WPS). It has only just started on these.

If it were you

One judgment: this is a template for "insider builds the tool + the founder films short videos," the opportunity is real and nobody is crowding in yet. But the entry ticket is industry identity, the product itself is the easiest part, the market is small, and how much money it can make is still unknown.

Who it fits: developers who come from a skilled trade, or who can find an experienced tradesperson willing to appear on camera every day as a partner; people working in non-English-speaking markets.

Who it doesn't fit: people with no industry background who only code, and people planning to acquire users through paid ads or SEO. These users won't search "pipe calculator" in the App Store. They install it because they saw a peer using it on a job site on TikTok. It also isn't for anyone aiming for a big business: a single trade in a single country probably caps out around tens of thousands of professional users (estimate).

How to build it: pick one trade and one language, then build the 10 to 20 things that trade calculates every day. Make it offline, no account, large buttons, and let people enter numbers. Release it free, treat the comments as your demand pool, and reply to every one. Once the rating reaches 4.8+ with dozens of real reviews, move advanced tools and export into a subscription, and post a video warning users before charging. Only later sell the multi-account crew and company version.

How to get users: the partner tradesperson films on real job sites, two videos a day. The captions can stay the same, but the footage has to be the work itself. Choose process questions that spark arguments in the comments, such as what machine to roll plate with or how to cut elbows. When insiders argue, that's traffic. Post the same videos to Instagram Reels and YouTube Shorts.

Timing: there's no rush, but first-mover advantage is clear. Once a well-reviewed free tool exists for one trade in one language, latecomers have a hard time breaking in. WeldUp is already expanding into other languages, so anyone who wants to do welding and pipe should move before it makes videos in Spanish and German. That probably gives you about the next six months.

Signs you've misread it: after this wave of videos passes (see late November), if the France Utilities chart falls back below #100, and Android daily installs drop back to a few dozen, it was just riding a few viral videos, and when content stops, the traffic stops. If, after the subscription launches, reviews mentioning "devenue payante" (became paid) keep piling up and the rating drops below 4.5, it means this professional audience won't pay for an individual tool, and the money can only come from companies.