ARLingHow we work

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
  • 18 tools live
  • 11 shipped since 4 September 2026
  • 1717 automated tests

On this page

01

Seven steps, in order.

Every tool goes through the same sequence, every time.

  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. Answer in the threads that started it.

    I go back to the original discussion and reply as myself, and point to the tool only where it is actually the answer, not as an ad.

  6. Measure for seven days.

    Self-hosted, anonymous 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

03

Privacy.

Nothing you type into a tool leaves your browser. No backend sees your Supabase keys, your redirect URIs or your source. The check runs where you are standing.

The only thing recorded is an anonymous 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.

Most tools stay free, on purpose. A free tool that solves one problem well gets used and shared in a thread. A paywall on a first visit does not.

One exception: the bank tools bundle for accountants (SEPA pain.001 Doctor, SEPA pain.001 Generator, camt.053 into Excel, Payment matcher) has an optional Pro licence, billed through Stripe. Each of those four tools keeps working, unlimited, without it.

Janii and bookapp are free public betas while we watch how people actually use them. Nothing here is a roadmap promise. A paid tier happens if and when it earns its place.

05

The tools so far.

18 tools, grouped by who they are for. 11 of them shipped since 4 September 2026, and every check is behind 1717 automated tests.

For developers

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

For accountants and companies

  1. 01 SEPA pain.001 DoctorSKTatra banka, SLSP, VÚB, ČSOB
  2. 02 SEPA pain.001 GeneratorSKExcel or CSV → XML for Tatra banka, SLSP, VÚB, ČSOB
  3. 03 camt.053 bank statement into ExcelSKTatra banka, SLSP, VÚB, ČSOB
  4. 04 Payment matcherSKA camt.053 statement against invoices from Pohoda, Omega, Money S3, SuperFaktúra
  5. 05 Bank tools for accountantsSKDoctor, Generator, camt.053 → Excel, Payment matcher: one Pro licence

Apps in beta

  1. 01 JaniiWindows app for wedding photographers, free beta, runs offline on your PC
  2. 02 bookappAndroid and Windows app, free beta, English and Slovak

06

What is free and what is paid.

One paid tier so far. Everything else stays free, with no limits.

  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 accounting tools are free on their own, with no limits.

    SEPA pain.001 Doctor, SEPA pain.001 Generator, camt.053 into Excel and Payment matcher each work unlimited without a licence.

  3. One Pro licence unlocks the bundle for accountants.

    Bank tools for accountants: 9 € a month or 79 € a year, billed through Stripe.

  4. Janii and bookapp are free public betas.

    No payment while we watch how people actually use them.

  5. 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 11 short answers to errors people keep searching for, each ending with the tool that checks it. All notes.

  1. SK
    Párovanie platieb z výpisu bez ručnej práce: VS, sumy a čo robiť, keď nesedia
  2. EN
    Error 400: redirect_uri_mismatch, explained character by character
  3. EN
    Supabase OAuth redirects to localhost in production: the allow-list rule nobody reads
  4. EN
    Expo + Supabase: why the OAuth deep link never comes back to the app
  5. EN
    Supabase Flutter deep link not working: scheme, Info.plist, AndroidManifest and the underscore bug

08

Questions, or a tool you wish existed.

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

andrej@arling.sk Back to all tools