modern-go-guidelines

Modern Go Guidelines

This repository contains guidelines for code agents that help them write modern Go code.

For example, an agent with these guidelines uses max(a, b) instead of an if-else block, slices.Contains instead of a manual loop, cmp.Or(a, b, c) instead of a chain of nil checks. It also knows about recent additions like new(42) to get a pointer to a value and errors.AsType[T](err) for type-safe error matching—both from Go 1.26.

The guidelines cover the most useful features from Go 1.0 through Go 1.26, including everything targeted by the modernize analyzer. An agent will:

• Detect the project's Go version from go.mod
• Use language features and stdlib additions available up to and including that version
• Prefer modern idioms over older patterns

Motivation

All coding agents tend to generate outdated Go. Two reasons:

1. Training data lag. Models don't know about features added after their training cutoff. They can't use errors.AsType[T] (Go 1.26) if they've never seen it.

2. Frequency bias. Even for features the model knows, it often picks older patterns. There's more for i := 0; i < n; i++ in the training data than for i := range n, so that's what comes out.

These guidelines fix both problems by giving the agent an explicit reference.

This aligns with the Go team's direction. The modernize analyzer exists to automatically update existing code to use newer idioms (see this talk from the Go team). These guidelines serve the same goal for new code: agents write modern Go from the start, so there's less to fix later.

Instructions

The guidelines are available for Junie and Claude Code.

Junie

Starting with version 2xx.620.xx, Junie includes the modern Go guidelines out of the box. No manual setup is required — just make sure you're running a compatible version.

Updating Junie

Go to Settings → Plugins → Installed, find Junie, and click Update if a newer version is available.

Configuration

The guidelines are controlled via Settings → Tools → Junie → Project Settings → Go. The Provide modern Go guidelines option is enabled by default. Disable it if you prefer Junie to generate code without these guidelines.

Claude Code

For convenience, the guidelines are distributed as a Claude Code plugin.

Installation

Run the following commands inside a Claude Code session.

1. Add this repository as a marketplace:

/plugin marketplace add JetBrains/go-modern-guidelines

2. Install the plugin:

/plugin install modern-go-guidelines

Usage

The plugin adds the /use-modern-go command. Run it at the start of a session to activate the guidelines:

/use-modern-go

The command detects the Go version from go.mod and tells the agent to use features up to that version:

> /use-modern-go

This project is using Go 1.24, so I'll stick to modern Go best practices
and freely use language features up to and including this version.
If you'd prefer a different target version, just let me know.

After this, any Go code the agent writes will follow the guidelines.