— Vert.x website

Vert.x is not a framework but a toolkit: the core library defines the fundamental APIs for writing asynchronous networked applications, and then you can pick the useful modules for your application (e.g., database connection, monitoring, authentication, logging, service discovery, clustering support, etc). Vert.x is based on the , a high-performance asynchronous networking library for the JVM. Vert.x will let you access the Netty internals if need be, but in general you will better benefit from the higher-level APIs that Vert.x provides while not sacrificing performance compared to raw Netty.

Because Vert.x was designed for asynchronous communications it can deal with more concurrent network connections with less threads than synchronous APIs such as Java servlets or socket classes. Vert.x is useful for a large range of applications: high volume message / event processing, micro-services, API gateways, HTTP APIs for mobile applications, etc. Vert.x and its ecosystem provide all sorts of technical tools for building end-to-end reactive applications.

Finally, it is worth mentioning that Vert.x is polyglot as it supports a wide range of popular JVM languages: Java, Groovy, Scala, Kotlin, JavaScript, Ruby and Ceylon. The goal when supporting a language in Vert.x is not just to provide access to the APIs, but also to make sure that the language-specific APIs are idiomatic in each target language (e.g., using Scala futures in place of Vert.x futures). It is well-possible to develop different technical parts of a Vert.x application using different JVM languages.