A weekly lab for small business ideas

Test one small idea every Sunday.

Every week I test a real business idea in public, with a budget under $100. You get the story, my real numbers, the mental model behind it, and the prompts to run the same test on your own idea.

Lab notebook · EXP-001 Running

Can I restart a quiet newsletter with free tools instead of tips?

“I believe people who want to start something on the side will sign up and use a free tool, because they want to start but don't know how to test an idea cheaply.”

Budget<$100
Runs14 days
Audience7,679

Day 1 of 14

  • Checked about 80 names, bought sundaylab.co ($29.99), drafted this page.
  • Clean up the old subscriber list and send a re-intro email.
  • Signups, replies, and how many people use a tool.

01 · The rules

Every idea has to pass four rules.

If it doesn't fit in one Sunday, it doesn't get tested. That's what keeps it small enough to actually start.

1 day

One Sunday

Build the test in a day or a weekend. No months of building first.

$100

Under a hundred

If testing costs more, find a smaller version of the idea.

1 person

Just you

No team, no hardware, no fragile integrations to maintain.

7 days

A number in a week

Decide up front what number means keep going and what means stop.

02 · How a Sunday works

Pick, test, decide.

Borrowed from The Lean Startup, Hacking Growth and The $100 Startup, and stripped down to what you can do in a day.

Step 1 · Pick

An idea that fits you

Start with what you already know and enjoy. Ideas close to your comfort zone are the ones you actually finish.

Step 2 · Test

The cheapest possible test

A landing page, 20 messages, a pre-sale. Write down your hypothesis: who will do what, and why.

Step 3 · Decide

Keep, change or kill

Look at your number after 7 days. A clear no is a good result too: it saves you months.

03 · What you get on Sunday

One idea, from story to test.

No list of 20 links. One idea, explained so anyone gets it, plus the thinking behind it so you can use it somewhere else. Short enough to read with your coffee.

Example issue

“Why a bar that's closed until 9pm is a business opportunity”

  1. 01The story. Something I saw or tried this week.
  2. 02My experiment. What I'm testing, with my real numbers. Including the bad ones.
  3. 03The case. One business that got big with the same idea.
  4. 04The mental model. Why it works, and three other places it applies.
  5. 05Your turn. A test for your own idea, plus two copy-paste AI prompts.

04 · Free toolkit

The tools I use, free with your first email.

The same templates I use for my own experiments. No upsell hiding behind them.

Interactive guide

The Seven-Day Idea Test

Type in your idea and your town once. Seven steps from idea to keep-or-kill, with prompts that fill themselves in.

Template

The Growth Board

One board for every experiment: ideas, tests, numbers and next steps, scored so you know what to try next.

Prompt pack

Prompts for each mental model

Copy-paste prompts for Claude or ChatGPT: find ideas that fit you, design the cheapest test, write your first 20 messages.

05 · Built around you

Ideas that fit the person, not just the market.

Most idea lists ignore who has to do the work. Tell me what you're good at, how much time you have and what you enjoy, and the ideas I send get picked with that in mind. Small, close to your comfort zone, and complementary to what you already do.

→

No chasing money in things that bore you.

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Start small enough to finish this weekend.

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Grow step by step as your skills grow.

275kfollowers on @startuplibrary
7,679readers waiting for the restart
EXP-001the experiment running right now

06 · Who runs the lab

Hi, I'm Erwin.

I've started and scaled a webshop, ran an event venue, grew an Instagram page to 275,000 followers and sold things I built. What I enjoy most is spotting opportunities and showing they're less complicated than they look.

Sunday Lab is me practicing what I preach. I test the ideas myself first, share what happened, and give you the tools to do the same.

07 · Questions

Before you join.

Is it really free?

Yes. The weekly email and the toolkit are free. If I ever build something paid, it will be a tool you can choose to use, and the emails stay free.

Do I need to code?

No. Most tests are a simple page, a message or a conversation. Where AI helps, I give you the exact prompt.

Why under $100?

Because cheap tests get done. The goal is a real answer from real people in a week, not a perfect product.

What if my test fails?

Then it worked: you found out in a week instead of a year. I share my own misses too.

08 · Join

Next Sunday's experiment, in your inbox.

One idea, one test, one honest result. Bring your own idea and run it alongside me.

Sign up at the top of the page →