Run
An interactive Cadence smart contract runner and playground for the Flow blockchain.
Run is an interactive Cadence development environment that lets you write, execute, and deploy smart contracts on the Flow blockchain directly from your browser. It combines a full-featured code editor with wallet integration, AI assistance, and GitHub-based deployment workflows.
Core Features
- Monaco code editor -- A rich editing experience with syntax highlighting, inline diagnostics, and auto-completion powered by the Cadence Language Server.
- Script and transaction execution -- Execute Cadence scripts (read-only queries) and transactions (state-changing operations) against Flow mainnet or testnet.
- Contract deployment -- Deploy or update Cadence smart contracts on any Flow account you control, with automatic add-vs-update detection.
- Cadence Language Server (LSP) -- Real-time type checking, hover documentation, go-to-definition, and auto-complete powered by a server-side LSP instance of the Flow CLI.
- Wallet integration -- Connect any FCL-compatible wallet (Lilico, Blocto, etc.) to sign transactions, or use custodial keys managed through the built-in key manager.
- Passkey-based signing -- Create and manage Flow account keys backed by WebAuthn passkeys for passwordless transaction signing.
- Cloud projects -- Save, load, and share multi-file Cadence projects with unique shareable URLs. Projects are stored via Supabase and support public/private visibility.
- AI assistant -- An integrated AI chat panel that understands Cadence and can help write, debug, and explain smart contract code.
- GitHub integration -- Connect projects to GitHub repositories for version-controlled contract deployment with environment management.
- Dependency resolution -- Automatically fetches and caches imported contract dependencies from mainnet or testnet so the LSP can provide full type checking.
- Multi-file projects -- Organize code into files and folders with a file explorer, tabbed editing, and project templates.
- Deploy dashboard -- A dedicated view for managing contract deployments across multiple addresses, with dependency graphs, audit information, and deployment history.
Tech Stack
| Layer | Technology |
|---|---|
| Frontend | React 19, Vite, TypeScript, TailwindCSS |
| Editor | Monaco Editor with Cadence TextMate grammar |
| LSP | Flow CLI cadence language-server (server-side process) |
| Flow | @onflow/fcl (Flow Client Library) |
| Auth | Supabase (GoTrue) with passkey support |
| AI | Vercel AI SDK (ai + @ai-sdk/react) |
| Server | Node.js (Express + WebSocket) |
| Production | nginx (static files) + supervisord (process management) |
How It Works
Run consists of two main components:
-
Frontend -- A Vite-built React SPA that provides the Monaco editor, file explorer, wallet UI, and execution controls. It communicates with Flow Access Nodes via FCL for script/transaction execution.
-
Backend server -- A Node.js process that hosts the Cadence Language Server via WebSocket and provides HTTP endpoints for GitHub integration. The LSP manages per-network dependency workspaces and translates between the browser editor and the Flow CLI language server.
In production, nginx serves the static frontend files and proxies /lsp WebSocket connections to the Node.js server and /functions requests to the Supabase edge function gateway for project persistence.