Langium is a next-generation language engineering framework for TypeScript that enables developers to build programming languages, domain-specific languages, code generators, interpreters, and compilers. It provides a "semantics first" approach where you define your language's grammar and abstract model simultaneously, offering built-in support for the Language Server Protocol to enable IDE integration across multiple editors. This framework is designed for language developers and tool builders who want to create custom languages that can run everywhere—from IDEs to browsers to CLI tools—without needing to reinvent the infrastructure for parsing, validation, and language services.