Agent Express

Agent Express provides a TypeScript‑based middleware framework for building AI agents that follows the familiar (ctx, next) pattern used by Express, Koa, and Hono. The core concepts are an Agent, a Session, and Middleware, allowing developers to compose functionality such as retries, cost tracking, memory management, tool integration, and guardrails as interchangeable layers around the main agent loop.

The library works with a wide range of language‑model providers—including Anthropic, OpenAI, Google, Mistral, Groq, and DeepSeek—via any compatible SDK. It supplies built‑in middleware for input/output validation, per‑session budgeting, token usage observation, tool execution, knowledge‑base search, PII protection, and session persistence backed by SQLite, Redis, or Postgres. Observability is supported through logs, OpenTelemetry metrics, and real‑time Server‑Sent Events, while testing utilities enable mock models and snapshot replay.

Targeted at developers creating production‑grade AI agents, Agent Express emphasizes minimalism and extensibility: every feature is a middleware component that can be combined, reordered, or replaced, and the framework is distributed as an ESM‑only, TypeScript‑strict package under an MIT license, requiring Node.js 20 or newer.