Test Your Launch on a Crowd of Fake Customers Before Real Ones See It: How to Run MiroFish With Claude
Most launches find out if people care after launch day. MiroFish, free and open source with 75,000 GitHub stars, builds a crowd of simulated customers from your page, your price or your ad, lets them argue about it on two fake social feeds, and tells you who bites, who swims off and why. How to set it up with Claude playing every one of them, what to give it, and what to ask
Most launches find out whether anyone cares on launch day, when it's too late to change the page, the price or the ad. MiroFish lets you run the launch first, on people who don't exist.
It's a free, open-source swarm simulator that passed 75,000 stars on GitHub in ten months. You give it material about your launch, and it builds a small world of simulated people, each with their own personality, memory and reasons. They post about your launch, reply to each other, like and pile on, across a Twitter-style feed and a Reddit-style one. Then it writes you a report, and you can ask any one of them why they did or didn't buy. Point it at Claude, and Claude plays every one of them.
What you get
| You give it | You get back |
|---|---|
| Your product page, saved as a PDF or text | A crowd built from the people and groups in your material, each with a profile of their own |
| Your price and your ad | Two simulated social feeds where they talk about it: posts, replies, likes, reposts |
| One question in plain words: will people love it or ignore it? | A written report: who's in, who's out, and the reasons that keep coming up |
| Follow-up questions | A chat with any single customer in the simulation: why didn't you buy? |
Change one thing (the headline, the price, the ad) and run it again, and you can see which version the crowd takes better before a real customer sees either.
How it works
- It reads your material and builds a map of who and what is in it: your product, your market, the kinds of people who'd buy or wouldn't.
- It turns those into simulated people, each with a profile of their own (an age, a job, a personality type, a backstory) and a memory.
- It lets them loose on a Twitter-style feed and a Reddit-style feed at the same time, round after round. They post, comment, like, dislike, repost and follow, and what one says changes what the next one thinks.
- A report agent goes through everything that happened and writes up the answer to your question.
- The world stays open: you can chat with the report agent, or with any one of the simulated people.
How many people you get depends on what you give it. MiroFish builds its crowd from the people and groups it finds in your material, so a page alone gives a small crowd, and a page plus a description of your audience, competitor reviews and a few forum threads gives a big one.
What you need
- Node.js 18 or newer, Python 3.11 or 3.12, and uv (Python's package manager). Or just Docker.
- A Claude API key from platform.claude.com. The simulation runs on the API, paid per use, not on a Claude chat subscription.
- A free Zep Cloud key from app.getzep.com. MiroFish keeps each simulated person's memory there, and the free monthly quota covers simple use.
Free, for your email
Get the full setup steps + the copy-paste setup prompt
The rest of this guide (7 more sections, 7 copy-paste prompts) opens right here. The setup prompt, one paste into Claude that sets it all up, comes by email only. Use your real address.
Unlocks: Step 1: get it running · Step 2: make Claude play everyone · Step 3: give it your launch · Step 4: run it, small first · Step 5: read the report, then ask the ones who swam away · +2 more
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