Underthesea is an open-source Agentic AI Toolkit written in Python. It offers multi-provider AI Agent support, allowing communication with LLM APIs from OpenAI, Azure OpenAI, Anthropic Claude, and Google Gemini using only Python's standard library, eliminating the need for specific client packages. The toolkit includes 12 built-in tools such as a calculator, web search, Wikipedia access, file I/O, and Python execution.
Key features include multi-session support for long-running agents with context reset and structured handoff, and automatic tracing of agent calls. A notable addition is the A2A-compatible HTTP server adapter (`underthesea.agent.server`), which wraps agents to communicate via JSON-RPC 2.0 `message/stream` over HTTP with SSE streaming. This adapter also provides a discoverable `AgentCard` and an optional bundled chat UI. The server is a raw ASGI callable, allowing integration with various ASGI servers like uvicorn, hypercorn, daphne, or granian. Each A2A `contextId` spawns a per-session agent clone, ensuring isolated conversation history, and tool calls stream live as artifacts.
Beyond agent capabilities, Underthesea integrates extensive Vietnamese NLP functionalities, including sentence segmentation, text normalization, word segmentation, POS tagging, chunking, named entity recognition, text classification, sentiment analysis, language detection, dependency parsing, translation, and text-to-speech.