JetBrains AI / Junie vs OpenCodeUpdated 2026-03-16

SUMMARY

JetBrains AI / Junie (IDE) uses markdown configuration while OpenCode (CLI) uses markdown. They differ on 5 of 11 compared features. Both tools provide AI-assisted development but take different approaches to project configuration.

FEATURE COMPARISON

FeatureJetBrains AI / JunieOpenCode
Config formatmarkdownmarkdown
Hierarchy support
Global config
Project config
Subdirectory scoping
File inclusion / imports
Ignore file.aiignore
IDE integrationCLI
Schema / structureFree-form (Markdown)Free-form (Markdown)
Git committed
EncodingUTF-8UTF-8

FILE MAPPING

PurposeJetBrains AI / JunieOpenCode
Settings / configuration.noaiopencode.json

SIDE-BY-SIDE CODE SAMPLES

JetBrains AI / Junie
.aiassistant/rules/*.md
markdown
# Kotlin Conventions

## Language Features
- Use Kotlin 2.x with coroutines for async work
- Prefer data classes for DTOs and value objects
- Use sealed classes/interfaces for domain errors
- Extension functions over utility classes

## Spring Boot
- Constructor injection (no field injection)
- Use @ConfigurationProperties over @Value
- Prefer WebFlux for reactive endpoints
- Use Spring Security with method-level security

## Testing
- JUnit 5 with Kotest assertions
- MockK for mocking (not Mockito)
- Testcontainers for integration tests
- Use @Nested for test organization

OpenCode
AGENTS.md
markdown
# Project Instructions

## Overview
This is a TypeScript monorepo using pnpm workspaces.

## Code Style
- Use strict TypeScript with no implicit any
- Prefer functional components with hooks
- All exports should be named (no default exports)

## Architecture
- /packages/core — shared business logic
- /packages/ui — React component library
- /apps/web — Next.js frontend

## Build & Test
Run tests with: pnpm test
Build all packages: pnpm build
All PRs must have >80% coverage on changed files.

## Conventions
- Use conventional commits (feat:, fix:, chore:)
- Prefer composition over inheritance
- See @docs/api-guidelines.md for API design patterns

KEY DIFFERENCES

1. Hierarchy support

JetBrains AI / Junie: Not supported. OpenCode: Supported.

2. Global config

JetBrains AI / Junie: Not supported. OpenCode: Supported.

3. Subdirectory scoping

JetBrains AI / Junie: Not supported. OpenCode: Supported.

4. Ignore file

JetBrains AI / Junie: .aiignore. OpenCode: Not supported.

5. IDE integration

JetBrains AI / Junie: Supported. OpenCode: CLI.

WHICH SHOULD I USE?

Recommendation

Choose based on your IDE/CLI preference. If you use JetBrains AI / Junie, configure .aiassistant/rules/*.md. If you use OpenCode, configure AGENTS.md. Many projects include config files for multiple tools so each team member can use their preferred editor.

PORTABILITY TIP

sync-instructions.sh
bash
# Maintain a single source of truth:
cp AI-INSTRUCTIONS.md CLAUDE.md
cp AI-INSTRUCTIONS.md .cursorrules
cp AI-INSTRUCTIONS.md AGENTS.md

SEE ALSO

agentconfig.ing2026-03-16COMPARE(1)