Using Spec-Driven Development for Production Workflows - Erik Hanchett, AWS

Hey everyone, my name is Erik Hanchett, and today I want to tell you guys all about spec-driven development and how you might use it in your workflows today. So there's a couple of things we want to talk about first: what is spec-driven development, and then how can it make you a better and faster coder.

So we just don't want you to code faster, but we want you to actually create higher-quality code from it, and I think really spec-driven development helps you with this, and I'm going to explain why and how. It's a structured.

Specifications are created before any code is written. That's the definition of really the specs, or the requirements of this spec-driven development, and it goes to the heart of what it is. So what we're doing is we are writing these markdown files, we're writing the specifications and the design document before any of the code is written, and this actually works really, really well with large language models and our coding assistants that we use, and I'm going to show you exactly how that works.

Now, a question I sometimes get is why. Like, why should we use this spec-driven development workflow, and then how can we do it. So to answer that why question, I kind of like to think about our coding assistants, our large language models that we're using every day, as sort of like AI interns.

You need to really prompt them, you really need to push them theright way, no pun intended, with the prompting. So you really need to guide them, because if you give them just a little bit of leeway, they will go off the rails, and really the spec-driven development helps guide them in theright direction.

I remember when I was an intern and one of my first jobs, we had a VP that would walk around and he would just come up with random ideas off the top of his head, and when he told me it, I would drop everything and work on it.

And then later my boss would be like, "Hey Erik, why did you drop everything." Well, the VP said something, and then I learned about, well, you got to take his information that he gives you, write it down, put it in your schedule, talk to me, talk to my manager about it.

So I was a little too eager, and this is what AI interns or basically these large language models do nowadays, and we got to be careful about it.

I didn't really give you too much of an introduction, so I'll give it to you now. My name is Erik Hanchett, I'm a Senior Developer Advocate at AWS. I have over 15 plus years of software development experience, and if you want to connect with me, you can check out LinkedIn, that's probably the best place to go.

Just look for Erik Hanchett, and yeah, talk to me, follow me, I'd love to talk to you more about it. Another question that people often ask me about spec-driven development is, "Can't the latest frontier models just do everything for us already?

Why do we need this." And while I do say that the models are getting better and better every year and every release, sometimes incrementally, sometimes by leaps and bounds, it's still not perfect, and giving the large language model these models more context is actually really important, because it does help guide it in theright direction, and with our software always changing and with the requirements always changing and with new paradigms and shifts, you always need to kind of guide it where it needs to go.

Some large language models, some harnesses are starting to think more about this and adding in a little bit more of a thinking or planning mode before it jumps into when it writes code, but there's nothing better than actually having those documents created and having you be in the middle before it jumps into that next part with it creating code.

So let's keep a few things in mind before we get too far. There is quite a lot of information out there. I have some opinions. These are my opinions. Let me know. Connect with me on LinkedIn if you agree or disagree, but I think you need to keep these in mind before using spec-driven development or vibe coding or anything in between.

We have to, you have to be careful with context. Now, I told you before that spec-driven development gives you a lot of context that gets fed into that large language model, but sometimes you have too much of a good thing.

What you need to do is, when you are working with these large language models, usually you create like an agents.md or a claw.md at the beginning with some information in it. I would be very careful not to put too much information or too little information in that.

Kind of like that Goldilocks zone of information is what you need. So you just need to give it enough rules and guidelines that it knows what to do.

We call it steering docs in Kiro, which I'll mention about in a minute, but you just got to be very careful what you put in those documents. I also highly recommend, when you're using spec-driven development, to use skills.

Skills are like instruction files that you can give to your coding agents that are ran on demand. So usually they have keywords in them, and when the coding assistant sees those keywords, they'll activate the skill, or you can do slash in the skill name and then run it, but this actually really helps when you're doing this spec-driven development process.

You can actually add skills when it creates your design documents or whatever else. You can use those in parallel or with the spec-driven development or when you actually implement the tasks.

And just be careful about giving too much trust. Remember, everything in the spec-driven development flow is you, meaning that you are the human in the loop, so to speak. You need to be the code reviewer of all the code that's generated through this process.

You need to be interactively looking at the design documents and the requirements documents that are created, because at the end of the day, if something goes wrong, you are the person that are going to be blamed for it, not the agent.

And that's not to say that we don't use tools to help do code reviews. Someone once told me, like, "Are you saying you're the human in the loop, you do the code review, no one else." Of course, we might have multiple people doing code reviews, and definitely use your normal AI coding assistants and review tools to help you review any pull requests that you create, or CRs.

So let me give you a little bit of a history lesson of where we have been, especially at AWS. We saw this need, especially from our teams and our customers, that they were vibe coding, they were using these coding assistants, but they weren't getting the outputs that they wanted.

And what we saw is this, these customers were using this bespoke pattern of having the agents, the coding assistants, create these full-on requirements documents and these design documents, and we decided to create an application to kind of do this all for them.

So we released Kiro

late last year in general availability. It's our new AI IDE coding assistant. We also have a command line interface, or CLI version, which is just as popular. I thinkright now it's switching. Most people are starting to use CLIs more often than IDEs, so if you like to do that, you can use the CLI.

But what we really focused in on with Kiro is, you can see in these screenshots, is this vibe and spec mode. So we're going to jump into spec mode in a little bit, but we really thought this really encompassed what we were hearing from our customers, that people wanted more ways to work with larger features and more complex projects, and they really needed the coding assistant to know exactly what their project was doing.

We also released the website at kiro.dev. Feel free to, after this presentation, to go check it out. You can download our CLI, our IDE, and give it a whirl, because we're really proud of it. It was fun. When we released this, it actually went a little bit viral.

We got tens of thousands of downloads. A lot of people were asking us, asking us about Kiro, so we were really happy to release this, and we actually, when we set it up in preview, we had so many downloads, we had to put a gate in front of it, and then people found around the gate, but now it is publicly available for everyone to try and give it a shot.

But I don't want this to be a half-hour pitch for Kiro. You can do this process, spec-driven development, without Kiro, and there's a few ways. One is that you basically, you have to just, you could do this manually with anything.

You could tell your assistant, your large language model, to include the following. First is the user requirements. You would tell them, "Please, based on XYZ, create a whole set of user requirements." Now you could feed it your own user requirements beforehand and say, "Okay, use this as a basis," or you can have the editor, the AI IDE, go ahead and create it for you.

Then you look back and forth with it, make sure it's okay, then you tell the assistant to create the design document, then you look back at that, and then you have it create the implementation details. These are the tasks list, the tasks one by one to actually implement it based on the requirements and the design document you created.

So you could do this kind of a manual way if you like.

I'll give a shout out to SpecKit. This is GitHub's open source way of doing this process. You can install it in a variety of different coding assistants.

Now in Kiro, you have this the IDE version. We have plan mode inside the CLI if you prefer the CLI, but in the IDE you would choose spec, and then you would go ahead and give it a prompt.

So in this case, I could say, like, "Build a movie MCP server to keep track of movies I've watched," or "Build a movie website," whatever you want. Now you're probably thinking, "Is this spec only good for Greenfield brand new projects," and I would say absolutely not.

I've seen existing apps that are years old have dozens and dozens of these different spec files in them. In this example, it's kind of more of a Greenfield, but you can definitely use it for existing legacy projects as well.

I think it works very well, and I would just say that these are really good for when you're doing in-depth features, when your project needs a little more upfront planning, and you just want to build things in a structured way.

Definitely works really well with complex projects. We actually added a spec mode for bug fixes too, so you can use it for smaller things, though you may want to just kind of vibe code those things instead.

Here's what our requirements document looks like. So in the first part, it creates this requirements phase where it's in this years format, and it gives you the introduction, like the requirements, the user stories. We also have a process where it asks you questions beforehand.

So we added in some extra question and answer, so as you put your prompt in, it'll ask you some clarifying questions before it creates this requirements phase. You can also do this quick plan mode we just added, which will go ahead and just generate all these documents quickly for you based on the questions and answers you give.

So there's a lot of different ways you can do this. Then you'll create a design document, which is a higher level design document. You can also start with the design document first. Some people kind of take this design and requirements and combine them, but typically with our spec-driven development flow, you could either start one or the other.

And then you might have mermaid diagrams here, ASCII art, with all the information. Now this is at the point I would highly recommend, if you're trying this at home, to stop and go in and update it with your knowledge and expertise and taste to exactly what you're looking for, because it's only as good as what you put in.

But you'll find out that even with a smaller prompt and with the clarifying questions, it does a pretty good job. And of course, you always want to review it for a markdown. The markdown file is for inconsistencies, hallucinations, and errors.

And then finally, you get to the implementation phase. This will be a list of tasks. It also has something called property-based tests in them, which are tests that are against the requirements document and design document. You can additionally have those created and ran.

I would highly recommend it, so that way it makes sure that the tasks actually are implemented correctly. I usually also, quick tip here, once it creates this task list, I tell it, "Please take the top four tasks, put them at the top, and create an MVP for me first," so that way I can actually see it working, and then I'll implement them, I'll implement the MVP version first.

Now I love model context protocol. I'm not going to go into exactly all the details of it, but it's a way, essentially, for your model providers to connect to different data sources. So in this case, I'm using Kiro, and maybe I'm using like OpenAI or Anthropic, and we want to connect to different data sources.

So we have this MCP protocol in the middle, and it connects everything together for us, which is awesome. Now I get this question, "Isn't MCP six months old and it's dead now?" Now a lot of people on the internet have opinions that change every other day, and some people were saying that, "Well, you can do a lot of stuff with MCP just with command line tools."

I really think MCP is still maturing. There's a lot, a long road ahead for it, especially with some of the security stuff it's doing. I would keep an eye out for MCP, but one of the main reasons I like it, especially for the spec-driven development flow, is you can have something like in Jira or Asana, all your tickets, all your large requirements docs, and then you can have it being pulled into your spec-driven development flow when it creates your specs, which makes it much easier to work with.

So if you have a product manager that has actually written a requirements document, you can pull that in.

And it just makes it a little bit easier. I'm talking about any kind of project management service, and grab technical details for it. You can also put additional rules in your steering or your agents.md files that tells it, "So if you're using spec-driven development flow, make sure you grab the information out of this MCP server," and that way it knows where to look.

Or you can just specify it in the first step, like, "Hey, look at this MCP server when you create the requirements."

So let me show you a quick demo. This is the latest version of Kiro, the IDE version, and let me give you a quick show of it. Now just for the sake of time, I don't have time to actually go in and create a brand new project from scratch, but I used this one.

It's a movie database, so this is more of a Greenfield brand new project, but I think you'll still get the idea. I was in the spec mode here. I said, "Please create me a movie website." So what it did is it started with this design document, and in this case, I actually told it to start with design instead of requirements, and then this shows the actual preview of the markdown file.

So you can see it created a bunch of different mermaid diagrams that show the architecture of it, gives you sequence diagrams, and so I went back and forth with this and updated and edited it, and it created this all for me.

If I scroll down to the bottom of this document it created, you can see here it created a bunch of property tests, and these are really special tests. It uses Fastcheck in this TypeScript in the Node world to do these tests, which I actually run dozens, if not hundreds of times with different values to make sure that

these requirements are satisfied correctly, which is really nice. And then it created this requirements document in, once again, this years format, so it's really very simple with these user stories, requirements. Let me see if I can open it up again.

Here's it in preview. So here's the requirements document. Requirements one: movie data loading. When the application initialize, the filter engine shall load. So it kind of gives you step-by-step exactly what it's doing here. And then when I went back and forth with this, I got to the task list and I asked it, "Hey, in the task list, can we create like an MVP?"

So it went ahead and updated the task list and even saysright here, "Task one through four, deliver a working MVP, browsable movie grid with search, genre filtering, sorting, and the full 80th way theme." So it actually redid all the requirements and to get this basically MVP up and running out of the door, which I really enjoyed.

I went ahead and just implemented all of them after that, but you could see how it works. You can also see it created this property-based tests, which are nice, which I can go back in and take a look at the execution.

You can also, let me see if I scroll to the bottom here. Here it is. So if I just kind of hover, it shows like a little bit of information about the property-based test. Like with property tests for genre filtering, for any movie dataset, the extracted genres list must contain exactly a sorted set of unique genres.

So it tells me exactly what it did at this point. So if you want to learn more, you can go to kiro.dev or you can join our Discord at discord.gg/kiro.dev. I highly recommend everyone watching. Check it out, and make sure you connect with me on LinkedIn at Erik Hanchett.

Love to just connect with as many people as I can, and also on BlueSky at ErikCH or X. Thanks.