01
Clone the starter
Each course ships a Go module with compiling stubs. The tests stay on the platform.
Learn by building
Ship the system. Then read the explanation.
Buildcraft is a membership for developers who learn by implementing real software from scratch. You stay in your editor. A small CLI uploads the project. We run the stage tests and show exactly what passed.
Three moves
How a stage works
02
Implement the contract
Instructions spell out types, errors, and the cases the grader checks. No hidden puzzle language.
03
buildcraft submit
The runner overlays the official tests and executes them in a sandbox with no network.
go · intermediate
Build Your Own Coding Agent in Go
Implement a coding agent in Go, one stage at a time. You start with a tiny OpenAI-compatible client and finish with the pieces a tool-using agent needs, including a loop, context limits, and permissions.
01A minimal LLM API clientSend a chat completion to an OpenAI-compatible endpoint and return the assistant text. Tests use a mock server, so you do not need an API key.Free02A chat loop with historyRead lines from the user, keep the transcript, and print each reply. The harness stubs the model with a function.Free03Tool calls and a registryParse OpenAI tool_calls payloads and dispatch them through a small in-process registry.Membership04A workspace file-read toolLet the model read files inside the project, and reject paths that escape the workspace.Membership05A file edit toolApply one unique search-and-replace edit inside the workspace.MembershipPreview06A shell toolRun a command in the workspace with a timeout and captured output.MembershipPreview07The agent loopAlternate model calls and tool execution until the model stops requesting tools.MembershipPreview08Context managementKeep the transcript inside a character budget without dropping the system prompt.MembershipPreview09Safety and permissionsGate each tool behind an explicit policy so a prompt cannot grant itself shell access.MembershipPreview
Membership
Start free. Stay for the rest of the build.
Free
$0
The first 2 stages. Same tests, same CLI, no card.
Open the courseMembership
Pro
Stages after the free ones, including previews as tests land. Stripe Checkout and the billing portal live on your account.
View membershipFAQ
Before you clone anything
Do I need an LLM API key?
No. Stage tests use a mock server or an injected function. Your code never has to call a real model to pass.
Where do I write code?
In your own editor and repo. Buildcraft grades an upload from the CLI. There is no in-browser IDE.
What is locked?
The first two stages are free for any signed-in learner. Later stages need an active or trialing subscription. Preview stages are readable by members but are not graded yet.