LangChain

Verification notes: MIT licensed. Official MCP adapters (langchain-mcp-adapters) and a public docs MCP server confirmed via LangChain's own documentation. Re-checked this pass: package and license unchanged, with the langchain-mcp-adapters library actively maintained (latest release July 2026). A2A still unconfirmed for core LangChain — there's an open, unresolved feature request for native langchain-a2a-adapters (langchain-ai/langchain issue #35724, filed 2026-03-10). Don't confuse this with LangGraph, a separate listing under the same company, which does now document native A2A support at the Agent Server level. Re-checked this pass: langchain-ai/langchain issue #35724 remains open and unresolved as of this check. The issue requests a separate langchain-a2a-adapters client package -- mirroring the existing langchain-mcp-adapters pattern -- that would let LangChain call remote A2A agents as tools; it is not a request for LangChain itself to expose a native A2A server. Either way, a2a stays false for core LangChain. See LangGraph's separate listing for the Agent Server's native A2A support, which is a distinct product surface.