How to Build Your First AI Agent: 8 Lessons From Building One in a Weekend

I’m not technically minded, and I built our first AI agent over a weekend. It answers the replies to our outbound campaigns and books the meetings. The build was the easy part. Getting it good enough to trust with real prospects took a method, and that’s what these eight lessons are.

1. Start With the Job Your Team Likes Least

Pick work that is repetitive, high volume and has a clear idea of good. For us it was answering replies across every inbox and LinkedIn account after one of our SDRs left. Prospecting is the usual answer for most sales teams: nobody misses it.

2. Fix the Foundations First

An agent is a small part of the process. If your emails don’t land, there’s nothing for it to answer. Before we built anything, our sending domains, inbox volumes, lead data and campaign copy were already in order.

3. Keep Someone From the Business in the Loop

We tried an outsourced developer first. The replies needed heavy editing and every change was slow. The agent has to learn your process and what good looks like for you, and that knowledge sits with you. So I dropped the developer’s framework and built it myself with AI coding tools.

4. Feed It Your Own Material

Ours learned from thousands of messages our SDRs had already sent, and from my own sent mail so it understood how I write. We turned that into a tone-of-voice guide it follows on every message.

5. Spend the First Two Days With It

I sat with it for two days and approved every draft. A “teach me” button let me apply a lesson to one campaign or to all of them. Always offering two meeting times, for example, became a rule everywhere.

6. Measure Edits, Then Automate One Campaign at a Time

We tracked how often a person changed a draft before it went out. When around 85% of a campaign’s replies went out with no edit, we switched that campaign to automatic. Then the next one.

7. Add a Reviewer, and Send Its Fixes Back to the Writer

A second agent now reads every draft, checks nothing is invented and gives the final approval. At first its suggestions came back to our team, which turned an automated job back into a manual one. The fix was to send them to the writing agent, let it make the edits and let the reviewer approve the result.

8. Decide What Always Goes to a Person

Pricing, objections it can’t answer and anyone asking where we got their details come to us in Slack. Every automatic reply waits 5 minutes before it sends, so a person can stop it. And the agent connects only to the few systems it needs, with no access to anything sensitive.

What Came Out of It

Over the 14 days to 28 Oct 2026 the agent’s median time to first reply was 6 minutes, including the 5-minute wait, and 8 in 10 of its messages went out with no human touching them. The full write-up of the talk these lessons come from is on demandguy.com.

Build Yours at Nerd Mode

At Nerd Mode in Amsterdam, Track 02 takes you from a blank screen to a working agent, and Track 03 takes this one apart on stage. Register your interest to hear the date first.