Evidence receipt / evaluation
Published · transcript-backedHamel Husain: evaluation
25 Sept 2025 Lenny's Podcast Why AI evals are the hottest new skill for product builders | Hamel Husain & Shreya Shankar (creators of the #1 eval course)
“There's a common trap that a lot of people fall into because they jump straight to the test like, "Let me write some tests," and usually that's not what you want to do.”
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- Speaker
- Hamel Husain
- Attribution
- Verified speaker
- Claim type
- evaluation
- Recorded
- 25 Sept 2025
- Publisher
- Lenny's Podcast
Transcript context
…Awesome. You guys actually brought an example of an eval just to show us exactly what the hell we're talking about. We're talking in these big ideas. So how about let's pull one up and show people, "Here's what an eval is." Yeah, let me just set the stage for it a little bit. So to echo what Shreya said, it's really important that we don't think of evals as just tests. There's a common trap that a lot of people fall into because they jump straight to the test like, "Let me write some tests," and usually that's not what you want to do. You should start with some kind of data analysis to ground what you should even test, and that's a little bit different than software engineering where you have a lot more expectations of how the system is going to work. With LLMs, it's a lot more surface area. It's very stochastic, so you kind of have a different flavor here. And so the example I'm going to show you today, it's actually a real estate example. It's a different kind of real estate example. It's from a company called Nurture Boss. I can share my screen to show you their website just to help you understand this use case a little bit, so let me share my screen. So this is a company that I worked with. It's called Nurture Boss, and it is a AI assistant for property managers who are managing apartments, and it helps with various tasks such as inbound leads, customer service, booking appointments, so on and so forth. It's like all the different sort of operations you might be doing as a property manager, it helps you with that. And so you can see kind of what they do. It's a very good example because it has a lot of the complexities of a modern AI application. So there's lots of different channels that you can interact through the AI with like chat, text, voice, but also, there's tool calls, lots of tool calls for booking appointments, getting information about availability, so on and so forth. There's also RAG retrieval, getting information about customers and properties and things like that. So it's pretty fully fleshed in terms of an AI application. And so they have been really generous with me in allowing me to use their data as a teaching example. And so we have anonymized it, but what I'm going to walk through today is, okay, let's do the first part of how we would start to build evals for Nurture Boss. Why would we even want to do that? So let's go through the very beginning stage, what we call error analysis, which is, let's look at the data of their application and first start with what's going wrong. So I'm going to jump to that next, and I'm going to open an observability tool. And you can use whatever you want here. I just happen to have this data loaded in a tool called Braintrust, but you can load it in anything. We don't have a favorite tool or anything in the blog post that we wrote with you. We had the same example but in Phoenix Arize, and I think Aman, on your blog post, used Phoenix Arize as well. And there's also LangSmith. So these are kind of like different tools that you can use. So what you see here on the screen, this is logs from the application, and let me just show you how it looks. l. And there's also LangSmith. So these are kind of like different tools that you can use. So what you see here on the screen, this is logs from the application, and let me just show you how it looks. So what you see here is, and let me make it full screen, this is one particular interaction that a customer had with the Nurture Boss application, and what it is is a detailed log of everything that happened. So it's called a trace, and it's just the engineering term for logs of a sequence of events. The concept of a trace has been around for a really long time, but it's especially really important when it comes to AI applications. And so we have all the different components and pieces and information that the AI needs to do its job, and we are logged all of it and we're looking at a view of that. And so you see here a system prompt. The system prompt says, "You are an AI assistant working as a leasing team member at Retreat at Acme Apartments." Remember, I said this is anonymized, so that's why the name is Acme Apartments. "Your primary role is to respond to text messages from both current residents and prospective residents. Your goal is to provide accurate, helpful information," yada, yada, yada. And then there's a lot of detail around guidelines of how we want this thing to behave.…
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