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How wework.

ARLing is a one-person company. I make the calls: which problem, when to stop, what gets built. AI agents do most of the actual work: research, code, tests, publishing, and watching for breakage. This page lays out that split, plainly.

  • 1 person
  • 34 tools live
  • 34 shipped since 4 September 2026 (all of them)
  • 4335 automated tests

On this page

01

Seven steps, in order.

Every tool goes through the same sequence, every time.

Four white A4 sheets fanned out on a dark desk, the top one carrying a round copper approval stamp impression, with a small graphite USB key lying beside them.
  1. Find a live thread.

    I read GitHub issues, Stack Overflow questions and forum threads where several developers are stuck on the same problem. It has to be deterministic: a config that is either right or wrong, not a matter of taste.

  2. Decide in 15 minutes.

    Is it narrow enough to check without running anyone's code? Does a good free tool already solve it? If so, we skip it. The point is filling a gap, not competing with one that is already filled.

  3. Build in under four hours.

    AI agents write the checking logic, the test suite, the page and the small hygiene work (favicon, sitemap, llms.txt, structured data) in parallel. If it is not done in four hours, it does not ship that day.

  4. Publish on arling.sk.

    No account, no email capture. Static HTML and JavaScript that runs entirely in the visitor's browser. A small number of tools later grow an optional paid tier; the check itself stays free either way.

  5. Reach people through channels, not threads.

    Andrej does not post in other people’s discussions. People find a tool through search, Google ads, social media where an agent publishes the posts, and Notes, short articles written for one exact error message.

  6. Measure for seven days.

    Self-hosted, pseudonymous analytics: page views, and which check people ran. Not what they typed.

  7. Keep or park.

    A tool that gets used stays exactly as it is. One that does not stays online, but I stop touching it. No tool gets a growing feature list just to stay alive.

02

Who does what.

The split does not move. I decide and answer. The agents research, build and watch.

Človek

  1. Which problem is worth solving
  2. Saying no to feature requests
  3. Money, domains, accounts, hosting
  4. The actual reply, in the actual thread
  5. Deciding a tool is done, or dead

The AI agents

  1. Researching the problem across issues and docs
  2. Writing the detection logic and its tests
  3. Building and styling the page
  4. Sitemap, llms.txt, structured data, favicons
  5. Watching for a tool quietly breaking

The illustrations on the ARLing pages are made by an image generator from our own written brief. Tool screenshots and photographs are real, and there are no generated images inside the books and PDFs.

03

Privacy.

Nothing you type into a file tool or a developer diagnostic leaves your browser. No backend sees your Supabase keys, your redirect URIs or your source. The check runs where you are standing. The services Proof, Renewals, Asistent and Stacklog are different: they run on a server, and each describes on its own page what it stores.

The only thing recorded is a pseudonymous count: a page view, a button clicked. That count comes from a self-hosted Umami instance, not a third-party analytics vendor, and it never sees the content of a form field.

04

How we make money.

Eleven developer Doctor tools, fourteen daily games and the contract templates stay completely free. SEPA pain.001 Doctor and Generator are free with no limit; camt.053 into Excel and Payment matcher process the whole file for free, but without a licence they download the first 20 rows. For the GDPR documents and the e-invoice, the preview and the check are free; you pay only to download the finished file.

Paid parts: GDPR documents (39 €), SEPA file check (149 €), the pain.001 fix in the browser (29 €), the e-invoice XML (2.90 € or 9.90 € for 30 days), Bank tools Pro (9 € a month or 79 € a year). Puzzle books: 4.90 € a book or 19.90 € for all ten. Other services are paid too, for example ARLing Asistent and Puzzle Post, with the price on their own pages.

Payment is by card through Stripe. The seller (merchant of record) is Link (Sold through Link, LLC) through the Stripe Managed Payments service; ARLing s. r. o. supplies the product. At checkout you will see “Sold through Link”, your bank statement will show LINK.COM* ARLING, and Link sends you the receipt. Digital content is delivered immediately after payment, so under Act No. 108/2024 Coll. section 19(1)(m) you lose the right to withdraw from the contract.

Bookapp stays a free public beta while we watch how people actually use it. A paid tier is not promised and only happens if it earns its place.

05

The tools so far.

34 tools, grouped by who they are for. The daily games count as one item and so do the puzzle books; everything we make is on Everything from ARLing.

For developers

  1. 01 Google OAuth redirect_uri_mismatch DoctorAny stack: NextAuth, Supabase, Firebase, Passport, Django, Laravel, Python, Expo, Flutter, Postman, gcloud
  2. 02 JWT DoctorAuth0, Supabase, Firebase, Cognito, Keycloak, Clerk, NextAuth, jsonwebtoken, jose
  3. 03 CORS DoctorExpress, FastAPI, Django, Rails, Laravel, Go, .NET, Supabase, Firebase Functions, S3, Cloudflare Workers
  4. 04 Stripe Webhook Signature DoctorNext.js, Express, Fastify, NestJS, Django, Flask, FastAPI, Rails, Laravel, Go, .NET, serverless
  5. 05 Firebase Auth Domain DoctorFirebase Hosting, Vercel, Netlify, custom domains, localhost, Capacitor/webview
  6. 06 Expo Universal Links and App Links Doctorapple-app-site-association, assetlinks.json, app.json
  7. 07 Redirect Loop Doctor (ERR_TOO_MANY_REDIRECTS)Sites behind Cloudflare, WordPress, nginx, Apache, Vercel, Netlify, load balancers
  8. 08 Cookie Doctor (SameSite, Secure, Domain)Front end and API on different domains, third-party iframes, Safari ITP
  9. 09 Supabase Auth Redirect Doctor for web appsNext.js, Vite, SvelteKit, Vercel and Netlify previews
  10. 10 Supabase Deep Link Doctor for Fluttersupabase_flutter, iOS and Android
  11. 11 Redirect Doctor for Expo and SupabaseExpo Go, development builds, standalone apps
  12. 12 ARLing MotionENTwenty animated UI components that also render as video

For companies, accountants and online shops

  1. 01 camt.053 bank statement into ExcelSKENDETatra banka, SLSP, VÚB, ČSOB, Sparkasse, Volksbank, UBS, any bank with camt.053
  2. 02 SEPA pain.001 GeneratorSKENDEExcel or CSV → XML for Tatra banka, SLSP, VÚB, ČSOB, DE profile per Deutsche Kreditwirtschaft
  3. 03 Payment matcherSKENDEA camt.053 statement against invoices from Pohoda, Omega, Money S3, SuperFaktúra
  4. 04 SEPA pain.001 DoctorSKENDETatra banka, SLSP, VÚB, ČSOB
  5. 05 SEPA file checkSKENDEYou send the file, within 24 hours you get a written report and the corrected file.
  6. 06 GDPR documentsSKCSDEPrivacy policy free, a bundle of 8 to 10 documents in Word.
  7. 07 Contract templatesSKUnder Slovak law. Preview and DOCX free, all five templates at once.
  8. 08 E-invoice check and builderSKENDECSEN 16931, Peppol BIS Billing 3.0 and XRechnung
  9. 09 AsistentSKENDESales assistant for online shops
  10. 10 Feed DoctorSKENDEProduct feed check
  11. 11 CV builderSKENDEA finished CV, no account
  12. 12 Mail DoctorENSPF, DKIM and DMARC of a domain
  13. 13 ProofSKENDECustomer approval before printing
  14. 14 RenewalsSKENDESupplier documents and renewal dates
  15. 15 StacklogSKENWhat a site runs on, and when it changed
  16. 16 Online shop checkSKWithdrawal, policies and cookies under Slovak law
  17. 17 EU sanctions checkSKENDEYour partner list against the EU sanctions list
  18. 18 RukopisSKENDEFinds stock phrases in your writing
  19. 19 AI to SI CheckerENSwitch AI to SI wording, keep law titles

For people

  1. 14 daily logic gamesHedgehogs, Magpies, Otters, Cranes, Swans, Voles, Squirrels, Herons, Badgers, Hares, Dormice, Owls, Beavers, Foxes. A year of archive going back, no account required.
  2. 01Puzzle booksTen books of 100 puzzles each, printable, with a free five-puzzle sample from every book. 4.90 € a book or 19.90 € for all ten.

Apps in beta

  1. 01 bookappAndroid and Windows app, free beta, English and Slovak

06

What is free and what is paid.

Free and paid, point by point. Other paid services, such as ARLing Asistent and Puzzle Post, list their price on their own pages.

  1. The 11 developer Doctor tools are free, with no limits.

    Redirect, deep link, universal link, CORS, JWT, cookie, redirect loop, Firebase and Stripe webhook checks: no account, no cap on how many times you run them.

  2. The four bank tools are free on their own.

    SEPA pain.001 Doctor and SEPA pain.001 Generator with no limit. camt.053 into Excel and Payment matcher process the whole file for free, but without a licence they download only the first 20 rows as a sample.

  3. Fourteen daily games and the contract templates are free.

    Hedgehogs, Magpies, Otters, Cranes, Swans, Voles, Squirrels, Herons, Badgers, Hares, Dormice, Owls, Beavers and Foxes with no ads and no account required; five contract templates with a preview and a Word download.

  4. For the GDPR documents and the e-invoice, the preview and the check are free.

    You pay only to download: the GDPR bundle of 8 to 10 documents 39 €, the e-invoice XML 2.90 € or 9.90 € for 30 days.

  5. The SEPA file check and the pain.001 fix are paid, one-off services.

    The file check with a written report within 24 hours 149 €, the self-service fix in the browser 29 €.

  6. One Pro licence works in three of the bank tools.

    SEPA pain.001 Generator, camt.053 into Excel and Payment matcher: 9 € a month or 79 € a year.

  7. The ten puzzle books are paid, with a free sample.

    Printable PDFs, 100 puzzles a book, the first five of each free to try: 4.90 € a book or 19.90 € for all ten.

  8. Bookapp is a free public beta.

    No payment while we watch how people actually use it.

  9. The e-mail list is optional.

    Only for new tools landing on arling.sk. Reply to any mail to be removed.

07

Latest notes.

5 of 139 short answers to errors people keep searching for, each ending with the tool that checks it. All notes.

  1. EN
    AI is now "Super Intelligence" in US federal agencies: what the order requires
  2. SK
    Dobropis a oprava základu dane: v ktorom období sa opravuje DPH
  3. SK
    Faktúra e-mailom v roku 2026: stačí súhlas zaplatením?
  4. EN
    It does not have HTTP ok status: what the CORS preflight (OPTIONS) request needs
  5. EN
    Redirect is not allowed for a preflight request: CORS, redirects and the trailing slash

08

Questions, or a tool you wish existed.

Write to support@arling.sk with the exact error message. Back to all tools.

support@arling.sk Back to all tools