A customer is charged twice
A slow payment gets sent again.
Fix: a unique key on every payment, so a retry can’t charge twice (an idempotency key).
35 short modules you read in your browser. Each shows how AI-built apps break with real users, and the prompt that fixes it in Claude Code, Codex or Antigravity.
Bad data gets saved
The AI changes how it answers. Your app saves it anyway.
Fix: check every answer before saving it (a validation gate).
An agent runs for hours
A step keeps failing, the agent keeps trying, and you get the bill.
A crash leaves bad data behind
One step of a job fails, and the steps after it keep going anyway.
Fix: save points that stop the run and go back to the last good state (checkpoints).
Can a second customer open the first customer’s page?
Sign up twice, in a normal window and a private one, and try to open one account’s page from the other.
Is the lock on every table in your database?
See whether the lock that keeps strangers out of your data is switched on, in the tool you built with.
Is a secret key sitting in your page?
Search your app’s page for secret keys that anyone could copy, and tell them apart from the keys that are meant to be public.
Start the free check
Fail a check and you get one prompt to paste into your AI. Free with an account.
Step 01
Understand the failure
A short story of one failure. Choose what to build and see what each option leads to.
Step 02
Write the spec
A spec is a plan for your own app that your AI builds from. The module helps you write it, then gives you the prompt to hand it to Lovable, Bolt, Replit, Cursor, Claude Code or Codex.
Step 03
Take the quiz
A short quiz to check you’ve got it.
The failure
A payment step timed out and the app kept retrying. 38 customers were charged four times in 90 seconds.
Your call
A refund request times out after the charge went through. Retry straight away, or give every refund a unique key first? You choose, then see where each path ends.
The fix
A unique key on every payment, and a check on every answer before it is saved. Also known as an idempotency key and a validation gate.
Your spec
You write the rules for your own payment step, with a checklist. It downloads as a text file you keep in your project.
Hand it to your AI
The module gives you the prompt and a checklist to check what your AI built.
Read my spec (attached or pasted here, or at docs/specs/validation-gates.md) before you write any code. … Show me the test output before you say it’s done.
- Send the same request twice with the same key: one row in the database.
- Send data in the wrong shape: nothing is saved.
Every module has the same parts, and ends with a short quiz to check you’ve got it.Start the free check
Stop double charges and bad data.
Foundations
Jobs that recover after a crash.
Multi-step jobs
Catch bad data early.
Data rules
Stop retries that run up your bill.
Retries and loops
Put it all together in one app.
Putting it together
Keep your AI agent under control.
Working with AI agents
Protect keys, accounts and data.
Security
See all 35 modules
Foundations
Multi-step jobs
Data rules
Retries and loops
Putting it together
Working with AI agents
How to stop users from seeing other users’ data
Make sure each customer only sees their own things.
What to do when your API key leaks
Switch the key off first, then keep keys out of your code.
How to stop retries from charging customers twice
Make a payment safe to retry, so nobody pays twice.
How to protect your AI feature from prompt injection
Stop text from strangers taking control of your AI feature.
How to stop an AI agent loop from running up your bill
Give your AI agent a spending limit and a rule to stop.
How to check a package your AI suggests is safe to install
Check a package is real before your AI installs it.
Your AI coding agent
Builds what you describe, fast. It adds the safeguards you ask for, and only those.
ArcLab shows you what to ask for, and gives you the spec and the prompt to hand over.
Documentation
Explains one tool at a time.
ArcLab starts from the failure and shows the fix across your whole app.
Tutorials and videos
Walk you through someone else’s demo project.
Every ArcLab module ends with a spec for your own app.
Trial and error
You find out from your users, or from the bill.
ArcLab shows you the failure first, in a scenario you can safely get wrong.
- 35 modules in 7 tracks, each ending in a final module that puts the track together
- A spec for your own app in every module: a checklist of what it must cover, that your AI builds from
- The prompt for Lovable, Bolt, Replit, Cursor, Claude Code or Codex, plus a checklist to check the result
- Bonus: the Build & Ship track, 9 modules on taking an AI product from idea to launch
- Lifetime access, including modules added later
- The free check: one complete module, “Is your app safe to share?”
- 10 free guides
- A workspace preview: the track maps and a short diagnostic
- Everything free, plus
- All 35 modules and the Build & Ship bonus track
- A plan for your app, a prompt and a checklist in every module
“I spent a year watching AI-built apps break in production. This is the system I needed.”
$29 one-time
Goes up to $49 after the first 100 members
14-day refund, as long as you haven’t completed more than one module.
What is ArcLab?
35 written modules you read online. Each one covers one way AI-built apps break with real users and ends with a spec for your own app, so your AI builds the fix.
Can’t I ask my AI to fix this?
Only for the problems you know about. Your AI builds what you ask for and leaves out what you don’t mention, like a check that stops a double charge. ArcLab shows you what to ask for, gives you the engineering term, and provides the spec.
I don’t know the engineering terms. Is that a problem?
No. ArcLab’s public pages explain every term in plain language, and the free check shows the approach on your own app before you buy. Inside, the modules use the engineering terms on purpose, because they are the terms you will give your AI, and each spec tells you exactly what to ask for.
Do I need to know how to code?
No. Your AI writes the code. You should have built at least one app with an AI tool. ArcLab is not for someone who has never built anything.
Is this a tool or something I read?
Something you read and work through. There is nothing to install. You read a module, choose what to build in a scenario, write a spec for your own app with the module’s guidance, and hand it to your AI. Each module ends with a short quiz.
What do I get?
All 35 modules in 7 tracks, plus the 9-module Build & Ship bonus track. Every module ends with a spec for your own app, the prompt to hand it to your AI, and a checklist to check the result. One payment, lifetime access, including modules added later.
Does ArcLab change my code?
No. ArcLab never touches your project. It shows you what to build and gives you the spec and the prompt. Your AI does the building, and you check the result against the module’s checklist.
Which AI tools does it work with?
Lovable, Bolt, Replit, Cursor, Claude Code, Codex, and any other AI tool you build with that takes a prompt. ArcLab does not plug into them. Each spec is a text file: add it to your project or paste it into the chat, use the prompt provided, and check the result against the checklist.
I only use Lovable or Cursor. How do I use this?
Download a module’s spec, attach it or paste it into the chat, then paste the module’s prompt. If you use Cursor, you can save the spec in your project instead. Some checks mention tools for a code project. If a check doesn’t fit, ask your AI to run it and show you what happened.
How long does it take?
Reading a module takes about 6 to 12 minutes. The scenario, the quiz and your spec take longer, depending on your app. There are no deadlines, and access does not expire for as long as ArcLab operates.
Do I need all 35 modules?
No. Your plan picks the first three. Open others when that problem shows up.
Does my progress follow me to other devices?
Yes. Your progress and drafts are saved to your account, so they’re there when you sign in on another device.
Can I try it before I buy?
Yes. Create a free account and run the free check, “Is your app safe to share?”: one complete module with three checks on your own app. If you buy and it is not for you, there is a 14-day refund, as long as you haven’t completed more than one module. The free check doesn’t count.
What if it isn’t for me?
14-day refund, as long as you haven’t completed more than one module. The free check doesn’t count. Email hello@arclab.systems and we refund the full price.
Are there limits I should know about?
Every module in the 7 tracks is open once you’ve paid, in any order; Foundations is the best place to start if you’re unsure. Only the Build & Ship bonus track goes one module at a time: pass a module’s quiz to open the next. Specs are text files you download; there is no plugin. The modules are written in plain English, and the guides have the code examples. The Working with AI agents track and parts of Security are written for tools that work on your files, with a GitHub repo. In Lovable, Bolt or Replit, some steps won’t apply. Prices don’t include sales tax or VAT. Lemon Squeezy adds it at checkout where it applies.
What happens after I pay?
Your workspace opens, usually within a minute. Sign in with the same account and start with the three modules your plan picks (you answer three questions when you first open the workspace). Foundations is the best place to start if you’re unsure.