Flue: A TypeScript Framework for Building Autonomous Coding Agents

Flue is a TypeScript framework for building autonomous agents using a programmable harness architecture — the same pattern behind Claude Code and Codex. It lets you define agents that plan, gather context, write files, spawn subagents, and run shell commands, all within a sandboxed environment.

Key Features

• Agent Harness: Combines a model (e.g., Anthropic Claude Sonnet 4-6) with a harness for tools like filesystem read/write, grep, glob, bash execution, and network access.
• Sessions: Persistent contexts for tracking work, similar to Claude Code or Codex sessions.
• Skills: Reusable workflows with structured output using Valibot for runtime validation.
• Sandbox: Built-in zero-config virtual sandbox, or connect your own remote sandbox. Fine-grained control over environment variables and token exposure.
• Deployment: Agents bundle into an HTTP server for remote use, or run via CLI (flue run) for local tasks and CI.

Example: AI Issue Triage in 22 Lines

import type { FlueContext } from '@flue/sdk/client';
import { Octokit } from '@octokit/core';
import * as v from 'valibot';

export default async function ({ init, payload, env }: FlueContext) {
  const { issueNumber } = payload;
  const agent = await init({ model: 'anthropic/claude-opus-4-7' });
  const session = await agent.session();
  const triage = await session.skill('triage', {
    args: { issueNumber },
    result: v.object({
      severity: v.picklist(['low', 'medium', 'high', 'critical']),
      reproducible: v.boolean(),
      summary: v.string(),
    }),
  });
  const body = **Severity:** ${triage.severity}\n**Reproducible:** ${triage.reproducible}\n\n${triage.summary};
  await (new Octokit({ auth: env.GITHUB_TOKEN })).request(
    'POST /repos/{owner}/{repo}/issues/{num}/comments',
    { owner: 'withastro', repo: 'flue', num: issueNumber, body },
  );
}

Who It's For

Developers building custom AI agents for code review, issue triage, data analysis, customer support, or coding automation who want full control over the agent stack without renting a third-party tool.