Krarkode

VS Code extension using Ark as the R kernel.

Supported platforms: Linux (x64, arm64) and macOS (x64, arm64). Windows is not supported — this extension relies on tmux for session management, which is not available on Windows.

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What Is This?

Previously, the go-to choice for using R in VS Code was the vscode-R extension. It is a great extension, but I still have some gripes with it: plot viewer backend format support, language server performance and correctness, data explorer experience, and more. Additionally, its LSP server and plot viewer require separate R packages to work.

Ark is a full-featured R kernel built by Posit. It ships with an LSP server, Jupyter comm protocol support, and a built-in plot device. However, using Ark natively in VS Code is currently not possible — it only works in Positron, the Electron-based IDE built by Posit.

That is why I built Krarkode: to bring Ark's R kernel experience into VS Code. This project has a strong personal bias; most design decisions serve my preferred workflow rather than being designed for generic use cases. I am a bioinformatician, mainly using R for data analysis and visualization rather than package development, and I don't use R Markdown at all, so package development and R Markdown-related features are out of scope for now.

Because my time is limited, I chose to glue multiple existing tools together (session management even uses tmux directly). The implementation is not the most elegant, but it works anyway. Most of the code was generated with the help of Claude Code and Codex. But I have put enough human intelligence into the design, and I won't be ashamed of the AI involvement.

The name, though seemingly hard to pronounce, means I cracked ark out of Positron and put it into VS Code.

See docs/design.md for design rationale.

Features (v0.1.0)

Session Management

• Create, attach, switch, stop, and interrupt Ark sessions
• Status bar shows real-time kernel state: idle / busy / starting / reconnecting
• Sessions persist across editor restarts (registry + connection file)

Code Execution

• Run selection or current line (Ctrl+Enter / Cmd+Enter)
• Source file with optional echo (Ctrl+Shift+S)
• Run from line to end / beginning to line
• Smart multi-line detection via Ark LSP's statementRange query
• Quick-inspect: nrow(), length(), head(), t(head()), names(), View()

Language Server

• Full R language intelligence: completions, diagnostics, hover, go-to-definition
• Auto-starts a background Ark instance for LSP when no interactive session is active

Plot Viewer

• Captures display_data from base R graphics, ggplot2, etc.
• History navigation, zoom controls, fit-to-window
• Save to file, open in browser
• Dynamic re-rendering on panel resize (via positron.ui comm)

Help Browser

• R help viewer inside VS Code with back/forward/home navigation
• In-panel search
• F1 at cursor looks up the function under point
• Ctrl+Shift+H to open

Variables Panel

• Real-time workspace inspector connected via positron.variables comm
• Expandable tree for lists and environments

Data Explorer

• Interactive data frame viewer launched via View() or the variables panel
• Column sorting, row filtering, column statistics
• Virtual scrolling (TanStack Virtual) for large data frames
• Column visibility toggle

HTML Viewer

• Displays show_html_file output: htmlwidgets, R Markdown, etc.

Pixi Environment Support

• Auto-discovers R binaries from pixi.toml in workspace or configured path
• Multi-candidate R binary picker when creating sessions

Logging

• 5 independent output channels: Runtime, UI, Ark Kernel, LSP, Sidecar
• Per-channel log level configuration (none / error / warn / info / debug / trace)

Doctor

• Krarkode: Doctor command checks R binary, Ark binary, sidecar, tmux, and Pixi environment status

Implementation Status

Requirements

• Ark binary — build from posit-dev/ark or extract from a Positron release
• R 4.1+ (no additional R packages required for Ark session management)
• tmux — used for session management (tmux driver mode only)

Configuration

Template variables available in command templates: {sidecarPath}, {arkPath}, {connectionFile}, {startupFile}, {sessionsDir}, {name}

Path settings support VS Code variable substitution: ${workspaceFolder}, ${userHome}, etc.

Development

pnpm install
cargo build --release --manifest-path ark-sidecar/Cargo.toml

# Build
pnpm run build

# Quality
pnpm run typecheck && pnpm run lint && pnpm run test:unit

# Package
pnpm run build && pnpm run package

Sidecar smoke test (requires pixi + R environment):

pixi run -- node scripts/ark-sidecar-lsp-test.js

License

MIT — see LICENSE.

Ark is MIT licensed. Krarkode uses only Ark's public protocol surface and binary interface; no Positron source code is included.

Related Projects

• posit-dev/ark — The Ark R kernel this extension is built around (note: the Ark team recently announced oak, which extracts the LSP server from Ark. This project may evolve once oak matures.)
• posit-dev/positron — Positron IDE, the primary consumer of Ark; source of inspiration for the UX this extension recreates
• vscode-R — The most classic VS Code R extension