Impossible ReAct Agent

A TypeScript template for an agent that reasons, calls local or MCP tools, observes their results, and continues until it can answer. It defaults to a local OpenAI-compatible model endpoint and also accepts any compatible hosted endpoint you configure.

ReAct means Reasoning and Acting. This repository is an agent runtime, not a React user interface.

Included

• current LangChain createAgent runtime backed by LangGraph
• local OpenAI-compatible model configuration
• built-in example tools and optional MCP tool discovery
• conversation threads with in-memory checkpointing
• step limits, request deadlines, cancellation, and graceful shutdown
• CLI, terminal JSON, and server-sent event HTTP entry points
• strict TypeScript, protocol-independent tests, integration tests, and coverage gates
• Docker, Compose, CI, security scanning, and release automation
• complete documentation and Impossible G repository artwork

Start locally

Use any server that exposes an OpenAI-compatible chat-completions API. The defaults expect Ollama on http://127.0.0.1:11434/v1 with qwen3:8b.

npm install
cp .env.example .env
npm run build
npm start -- --input "Count the words in: local models belong to you"

On PowerShell:

Copy-Item .env.example .env
npm run build
npm start -- --input "What time is it?"

HTTP API

npm start -- --serve

curl http://127.0.0.1:4141/v1/chat \
  -H "content-type: application/json" \
  -d '{"input":"Count the words in this sentence","threadId":"demo"}'

Health and readiness routes are available at /healthz and /readyz. For incremental model output, send the same request body to /v1/chat/stream and consume the server-sent events.

Add MCP tools

Create a configuration file:

{
  "mcpServers": {
    "local-tools": {
      "command": "node",
      "args": ["../impossible-mcp-template/dist/cli.js"]
    }
  }
}

Set MCP_CONFIG_PATH to its path. Tools from every configured server become available beside the built-in examples.

Commands

Command	Purpose
npm run dev -- --input "..."	Run one prompt with source files
npm run dev -- --serve	Start the development HTTP API
npm run build	Compile the production package
npm test	Run tests once
npm run test:coverage	Run tests and enforce coverage gates
npm run verify	Run formatting, linting, types, coverage, and build

Documentation

• Architecture
• Models
• Tools and MCP
• HTTP API
• Configuration
• Operations
• Testing

License

MIT