Flue

Flue is an agent runtime framework developed by the Astro team (withastro org), positioned as "The Agent Harness Framework." It provides Claude Code-like agent orchestration capabilities but entirely without TUI/GUI, exposed as a pure TypeScript SDK that gives developers fine-grained programmatic control over agent lifecycle, tool injection, sandbox environments, and output structures.

Core features include: a default virtual sandbox based on just-bash (no containers required), a multi-tier sandbox system supporting local filesystem and remote containers (e.g., Daytona), Markdown-driven Skills/Context definitions with auto-discovery, Valibot-based Typed Result Schema validation, Session persistence with sub-agent (Tasks) mechanism, three-level Role override (agent/session/call), Remote MCP Tools support (streamable HTTP and SSE), and a Connector design delivered as Markdown installation instructions.

Flue is runtime-agnostic, deployable to Node.js, Cloudflare (with Durable Objects persistence), GitHub Actions, GitLab CI/CD, and more. Agents can be exposed as HTTP endpoints by declaring triggers = { webhook: true }. Typical scenarios span the full spectrum from simple tool-free agents (e.g., translation) to full coding agents (remote containers + MCP + privileged CLIs).

The project is currently in Experimental status with APIs subject to change. It uses pnpm workspace + Turborepo for monorepo management, with core packages @flue/sdk and @flue/cli, requiring Node.js ≥ 22.

Agent Programming Model#

• Each agent file exports triggers (trigger declarations) and a default async function (handler) receiving FlueContext (with init, payload, env)
• Initialization chain: init({ model, sandbox, providers }) → agent.session() → session.prompt() / session.skill() / session.task()
• Model format: provider/model-name, e.g., anthropic/claude-sonnet-4-6, openai/gpt-5.5

Sandbox System#

• Virtual sandbox (default): based on just-bash, no containers, suitable for high-traffic scenarios
• Local filesystem sandbox: sandbox: 'local' mounts the host filesystem
• Remote container sandbox: via Connector adapters (e.g., Daytona), providing full Linux environments
• Custom sandbox: supports passing custom Bash factory functions

Tools & Integrations#

• Privileged CLI injection: defineCommand() injects CLI tools with environment variables on demand (e.g., gh, npm)
• Remote MCP Tools: supports streamable HTTP (default) and SSE transports for connecting to remote MCP servers
• Connectors: third-party service adapters delivered as Markdown installation instructions, executed by AI coding agents via flue add <connector>

CLI Commands#

Unconfirmed Information#

• Whether @flue/sdk and @flue/cli are published to npm public registry
• Current main branch version number not explicitly labeled
• Full LLM Provider support list
• Detailed Cloudflare deployment documentation