The harness is all you need (mostly)

If you’re feeling overwhelmed by AI right now, you’re not alone.

Every day it seems there is a new tool, new MCP, new model, new skill, new workflow, new feature, new social post that is some form of “Hey look! I have completely figured out AI with this one weird prompt.”

I…don’t believe you.

I work with AI every single day, and what I’m finding is that less is way more. It’s not about what I install or configure or trick the agent into doing that makes any real difference. That stuff is interesting, but at the end of the day it feels like gimmicks.

I see the biggest gains in my productivity from how I use the harness and how well I understand it.

So in this post, I’m sharing you a simple workflow that you can use to drastically improve your effectiveness with AI just by using existing features of GitHub Copilot. No weird prompts. No skill everyone else seems to know about. Just the harness. The harness is all you need—mostly.

Disclaimers

I’m using the term “harness” interchangeably with “GitHub Copilot.” The point of this post is to keep things simple, so just know that GitHub Copilot is an agent harness.

I don’t mean to insinuate that you won’t ever need any skills or MCPs or instructions or custom agents, etc. In fact, those things will become quite important as you progress and need to define complex workflows and automate things for your teams. In fact, I use a few throughout this blog post!

What I am pointing out here is that you do not need any of those things to be highly successful with AI.

Also, there is a lot of slop out there. If you don’t believe that, ask the agent to create a skill to do anything at all. It will happily oblige. Whether or not that generated skill actually works, it can be easily published to any number of skill or MCP registries.

1. Pick a tool, any tool

This is an obvious one, right? Pick a tool! It’s so easy!

But even within the GitHub Copilot family, there are a lot of options. These include the CLI, the new GitHub Copilot app, VS Code, Visual Studio, and JetBrains, just to name a few.

The good news is that these experiences are increasingly being centralized on the same harness. The details can differ by tool, but the core workflow is consistent. Learn the harness once, use it everywhere.

That said, I do believe that learning the harness is key, and the best way to learn it is to be as close to it as possible. So if you are just starting out, I’d recommend beginning with the GitHub Copilot CLI. It’s a terminal interface, which means it’s just text. There isn’t much UI to learn. You enter a prompt. The agent does things. But the interaction is more direct, immediate, and, frankly, very satisfying.

For this demonstration, I’ll be using the new GitHub Copilot app. But the harness that app uses is the exact same thing you’ll be using if you are using the GitHub Copilot CLI, Visual Studio Code and many other places you can find GitHub Copilot.

2. Turn on YOLO mode

YOLO mode is also known as “Allow All.” This lets the agent execute any command without asking permission. This can vary depending on the tool you are using, but for most it is simply an /allow-all command in the chat. Otherwise, the agent is going to stop and wait for your approval every single time it needs to do some work.

Agents need autonomy for you to see an increase in productivity. If you have to approve everything the agent does, you might as well just do it yourself. Besides, that’s a miserable user experience. Nobody wants to be relegated to sitting at a desk pressing the “Approve” button all day. And pressing “Approve” over and over just trains you not to read what you are being asked to approve, which defeats the purpose.

You want to be safe with agents, though. Bad things happen to good people. When using YOLO mode, you don’t want to run the agent on your local machine. This is especially true when you are using them at work—data is private on your organization’s systems, and mistakes can be costly.

Fortunately there are a bunch of options for running agents in sandboxes. An easy one to get started with is GitHub Codespaces or development containers.

3. Start with a prototype

One of the most magical things about AI is that you can easily prototype anything and everything up front. Historically, this was not the case. Prototyping was a full phase of a project, and were often a luxury. Now, you can make one with a prompt.

Let’s look at a few examples.

Let’s say we want to build a date picker web component. That seems straighforward, but it’s actually quite complex. Think of all the different things you might want to do with it.

• How do you navigate within the component?
• What does the selected date look like?
• What does a selected range look like?
• How does the user navigate between days, months, and years?

Start with a simple prototype and get several variations. I usually start with something like this:

Give me 20 mocks for a date picker web component. Put them all in an HTML file so I can compare.

In this case, the AI generated a bunch of different layouts, but one of them is a mock where it starts with the year view. That’s interesting. I would like my date picker to enable the user to zoom out to the year, then into the month, and finally to the day. These are the kinds of things you don’t consider until you see them.

As humans, we process sensory-rich models like images, shapes, and tangible layouts much faster than dense text. Creating low-effort prototypes early on helps make complex concepts immediately intuitive.

And this applies to non-visual tasks as well.

For instance, if I want to add a new API endpoint, I’ll still create a visual prototype to understand the requirements and constraints before diving into the implementation.

Create a visual mockup of the API for this project. Add five options for how we could handle a new API endpoint that allows the user to download their analytics data.

Since the GitHub Copilot app supports Mermaid diagrams, the agent renders this as Markdown, mapping out five different ways we could implement this API endpoint.

When working with agents, it’s easy to forget that everything is nuanced. Prototyping helps uncover the nuances up front, so you avoid spending valuable time and tokens on rework.

I recommend using a medium-sized model, such as GPT 5.6 Terra or Claude Sonnet, on medium reasoning for most work. I also recommend you stick with whatever model you choose here for the duration of this particular feature, bug, or enhancement. Prompt caching will save you tokens. As long as you don’t switch to a different model or reasoning level, your previous chats remain cached with the model, giving you a discount on future requests.

4. Plan methodically

Now that you know what you actually want versus what you initially thought you wanted, it’s time to plan out the implementation.

Switch to plan mode in GitHub Copilot without starting a new session.

“/plan Build a date picker web component. I want the user to be able to zoom in and out of years, months, and days.”

That’s a pretty vague prompt, and you’ll likely have more context for the model than I do here, but this is just a demonstration. If you don’t have more context, it’s OK. That’s exactly what this step is for.

In theory, you can get a model to one-shot anything if you compose the perfect prompt with the perfect context in the perfect order. In theory.

But none of us can do that. Planning helps you get closer to that ideal, though, by asking all of the questions that you would need to answer yourself along the way if you were to build this out by hand:

• Can the start and end date be the same?
• Are partial selections valid?
• Should users be able to clear the date?
• Should “today” always be a visible option?
• Is manual entry allowed?
• What format is the date stored in?
• Should pasting in dates be allowed?

The list goes on and on. You cannot possibly think of all of these edge cases, but the model can help you identify many of them.

You can m…