A simulated civilization with 22,000 AI agents

Edition 120 | September 18, 2025

I want to say there are better things to do with the time your agents save you than mindlessly scrolling brainrot, but if we’re being honest, mindlessly scrolling brainrot is how I find these tweets.

Welcome back to Building AI Agents, your biweekly guide to everything new in the field of agentic AI!

Researchers in Hong Kong are using a massive civilization of AI agents with its own simulated economy to study the dynamics of real human societies.

In today’s issue…

• The AI agent civilization

• An “app store” for MCP servers

• Agents help seniors monitor their blood pressure

• 10 hacks for transforming business workflows with agents

• How a solo agent builder made $60k in 3 months

…and more

🔥 IN CASE YOU MISSED IT

Readers’ favorite items from the past week

1. OpenAI’s tips for prompting gpt-realtime

2. An e-book on the essentials of AI engineering

3. How (not) to build a successful agent startup

4. Microsoft’s agent for automating companies’ R&D

5. A self-hosted agent to automate your computer tasks

 🤖 AGENT OF THE WEEK

This guide walks you through building an AI Website Roast Agent that takes any landing page, roasts it like a stand-up comic and then emails the roast straight to your inbox. Built in n8n with GPT-4.1, Gmail, and a form trigger, it’s a fun yet practical way to get instant feedback (and laughs) about your site.

💡 The best part? We made it live so you can test it —> Try the agent

Drop in your URL (or even your favorite competitor’s site), and the roast will be generated and emailed to you.

Step-by-Step

1. Open up n8n: Create a new workflow (free plan is enough)

2. Add your model: I used GPT-4.1 mini, but you can swap in Claude, GPT-5, etc

3. Set up the roast agent: Prompt tells the model to act as a savage but insightful website roastmaster

4. Scrape the site: The agent pulls in your landing page content

5. Format the output: Structured the email body into Roast → WTF Moments → Fixes (Messaging, Design, Trust)

6. Send it by email: The gmail integration delivers the roast directly to the email provided

7. ⚡ Not super practical, but fun — and the setup can be repurposed for CRO audits, conversion analysis, copy reviews, and more

Bonus: We’ve put together a detailed video walkthrough and the exact n8n agent template. Access both in our Building AI Agents Community here!