adk-js

Agent Development Kit (ADK) for TypeScript is Google's open-source, code-first toolkit for building, evaluating and deploying AI agents. You define agent behavior, orchestration and tool use directly in TypeScript, which the README says makes them easier to debug, test and version and lets them run from a laptop to the cloud. It is aimed at developers who want fine-grained control and tight integration with Google Cloud services. The same family has Python, Java, Go and web versions.

Install it with `npm install @google/adk`. The README's example creates an `LlmAgent` with a name, description, model (the sample uses `gemini-2.5-flash`, or your preferred model), an instruction and the built-in `GOOGLE_SEARCH` tool. Key features it lists are a tool ecosystem (pre-built tools, custom functions, OpenAPI specs), code-first development and modular multi-agent systems composed into hierarchies. It also describes a built-in development UI for testing, debugging and showcasing agents.