modelcontextprotocol/kotlin-sdk

The Model Context Protocol (MCP) Kotlin SDK is a high-defensibility infrastructure project due to its status as the 'official' implementation maintained in collaboration between Anthropic and JetBrains. Its 1,300+ stars and 200+ forks reflect rapid adoption within the JVM ecosystem. The primary moat is not just the code, but its position as a protocol standard-bearer; developers building MCP-compliant tools in Kotlin will default to this SDK to ensure compatibility with Claude and other MCP-supporting LLMs. Frontier risk is 'low' because the frontier labs (specifically Anthropic) are the architects of this ecosystem, not competitors to it. The collaboration with JetBrains is a strategic masterstroke, ensuring deep integration with IntelliJ IDEA and Fleet, which creates significant ecosystem lock-in. While other protocols exist (e.g., LangChain's various integrations), MCP is quickly becoming the 'USB port' for LLM context, and this SDK is the primary driver for that on the JVM.