Introducing Beast Mode 3.1

Beast Mode 3.1 is here.

What is Beast Mode? Great question! It is a custom chat mode for VS Code that turns your agent into a Beast.

👉 Get Beast Mode

Here’s how it works.

1. Grab the raw markdown from this gist.
2. In VS Code, go the “agent” dropdown in chat and select “Configure Modes”.
3. Select “Create new custom chat mode file”.
4. Choose “User Data Folder”. (this makes it global to all projects)
5. Paste in the contents from the gist.

And now all you have to do is activate Beast Mode from the dropdown.

YES BUT WHAT IS IT?

It’s just a prompt. That’s all it is. But as it turns out, prompts matter a lot. They are the programming language of AI. Beast Mode builds on OpenAI’s official 4.1 cookbook coding agent example and layers in a highly opinionated workflow that is modeled after how an actual developer might work to solve a problem, implement a feature, etc. It is specifically designed to be used with GPT 4.1, but people are reporting a lot of success using it with Claude and other models as well.

Why Beast Mode?

GPT 4.1 is a very compelling model for agentic coding. The reason for this is that it’s crazy fast. While Claude is highly accurate, it can also be painfully slow. It’s also considered a “premium” model in Copilot which means that you are capped at a certain number of requests.

The problem with 4.1 is also that it is very fast. It speaks before it thinks and it wants to finish as quickly as possible. This means that it has two rather serious drawbacks…

1. Lack of Agency
2. Lack of Accuracy

Beast Mode was originally created to address both of these issues.

Increasing Agency

4.1 likes to say it’s going to do things and then just not do them. It talks a big game, and then doesn’t deliver. For instance, it’s common when working with agents to just paste errors in from the console or browser verbatim and expect the agent to just fix it. Here is what 4.1 does by default when you do this…

The 4.1 cookbook coding agent example is an eye opening look at what it takes to get 4.1 to just do things instead of talking about them. Essentially the entire top of the prompt is dedicated to telling 4.1 to just do things. In Beast Mode, much of this is verbatim from the 4.1 docs with added emphasis. The model is told 8 times in about 8 different ways to keep working until a problem is fully resolved before ending it’s turn.

While this was an improvement, I found it wasn’t enough. 4.1 still wanted to end its turn before the job was done. One of the emerging patterns for agents is to work in todo lists. The Copilot Coding agent in GitHub does this. While it’s working on a PR it puts a todo list in the PR and checks off items as it goes. I added one of these to 4.1 and found it made a pretty big difference. It’s as if being forced to constantly update the user on the status of work with a todo list makes 4.1 much more likely to actually complete a task all the way through. Here is the same error as before, but with Beast Mode…

I had to cut the screenshot off, but essentially Beast Mode just goes directly to work. It plans, creates a todo list and then starts working.

Increasing Accuracy

The planning is part of increasing the accuracy, and again, a lot of this comes from the 4.1 cookbook coding agent example. I did modify it to get the model to ask itself some questions before it starts working. I found that it really doesn’t want to think, but having it ask itself questions seems to help with this quite a bit…

2. Understand the problem deeply. Carefully read the issue and think critically about what is required. Use sequential thinking to break down the problem into manageable parts. Consider the following:
   - What is the expected behavior?
   - What are the edge cases?
   - What are the potential pitfalls?
   - How does this fit into the larger context of the codebase?
   - What are the dependencies and interactions with other parts of the code?

Otherwise, I found 4.1 to be quite sloppy. It just doesn’t care about the fact that systems are complex and you have to really think about what you are doing before you make any changes at all. Saying “think deeply” or “take a deep breath” doesn’t work. It’s like telling a five-year-old on a sugar high to calm down.

Thinking is only part of increasing accuracy though. The other important part is forcing 4.1 to use the internet to get information. It needs all the context it can get. Even if it knows that something won’t work, it will do it anyway. For instance, even if it knows that you are using shadcn/ui, it will act like it has no clue how to use that library and just make up its own components.

The solution to this is to make it do what any good developer would do - use Google. VS Code ships a very powerful tool called fetch out of the box for the agent. Fetch actually uses a headless browser in the background and it returns web content as markdown. Beast Mode forces 4.1 to use this tool recursively to search the web and get information before it acts.

Here is a video of Beast Mode implementing a redesign and you can watch it go out to the shadcn/ui docs and recursively crawl the content to get information it needs to use components correctly.

What’s in Beast Mode 3.1?

Beast Mode 3.1 has a few minor updates from v3.

Memory

I’ve added a section for a memory. This is similar to how memory works with ChatGPT if you’ve used it before. What it does is allow you to tell the model to remember things. Those “things” are saved in a .github/instructions/memory.instructions.md file - which is automatically created for you if it doesn’t already exist and will be automatically added to any future prompt.

This is useful for when the model keeps making the same dumb mistake over and over again. Just tell it to remember not to do something or remember some aspect of your project and it will write that to its memory.

Improved file reading and writing

OpenAI designed 4.1 to be good at tool calling and that’s great - but it’s also a problem. It will frequently read things that it has already read. I’ve seen it read the same folder/file 10 times in a row. I’ve added a section here to give it specific instructions about when it’s OK to re-read a file or folder.

Rendering prompts as markdown

A lot of times I ask it to take my prompt and boost it - or write a prompt for me. It will do this with no problem, but it spits the result back out in chat in a way that isn’t easy to copy. I always want my prompts in markdown, so if you tell it to write or boost your prompt, it will give it back to you in a markdown block that you can easily copy.

Git

I don’t go to the sidebar anymore to stage and commit. I just tell the agent to do it whenever I’m satisfied with a particular interaction. The problem is that with 4.1, after a while it will just assume it’s fine to stage and commit whenever it wants. I added a section to the prompt to tell it to only stage and commit when I tell it to - very simple.

Activate Beast Mode

Give Beast Mode a spin. Remember that it is quite an opinionated way of working, so tweak it to your liking. Give the instructions at the top of the gist a good read before you use it, so you understand how tools work in the front matter.

Unleash the beast.