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Eclipse LemMinX

Thursday, November 21, 2019 - 12:30 by Fred Bricon
This proposal is in the Project Proposal Phase (as defined in the Eclipse Development Process) and is written to declare its intent and scope. We solicit additional participation and input from the community. Please login and add your feedback in the comments section.
Parent Project
Proposal State

Many editors are now compatible with the Language Server Protocol (LSP). Several languages (Java, TypeScript, etc) now have a full-featured LSP implementation, but a powerful XML language server is missing from the ecosystem.


The  LemMinX project provides an LSP implementation for the XML language (aka XML Language Server). It can be used with any editor that supports the protocol, to offer editing support (completion, hyperlink, validation, hover, codelens, ..) for XML documents (.xml, .xsd, .xslt…), as well as schema-based (XSD and DTD) validation.


The XML Language Server is extensible via a plugin system (based on a service provider interface - SPI) to provide completion, validation, etc. 


LemMinX provides an implementation of the LSP for XML, written in Java, and based on the Eclipse LSP4J framework.

It implements most of the language server protocol features to provide XML editing support while also exposing extension points for 3rd party adopters to provide custom features via a plugin system. 

Here are some plugin examples:

  • XML syntax/matched grammar validation, via the Xerces XML validator

  • XML completion based on grammar, via Xerces

  • Proof-of-Concept plugins like Maven, emmet or web.xml extensions. 

LemMinX is reusable as a Language Server for downstream projects, but some components, such as the fault-tolerant parser or the service layer can also be reused directly.

Why Here?

LemMinX's XML Language Server is based on the Eclipse LSP4J project. Being part of the Eclipse Community would allow closer collaboration and consumption with/from other related projects and communities, like Eclipse Che, Eclipse LSP4E, Eclipse Wild Web Developer.

Additionally, the project would benefit from being inside the community by attracting more experienced Eclipse developers who're already contributing to some related projects.

Project Scheduling

An initial release based on the initial contribution is planned after the project creation.

Future Work


  • Continuous adoption of newer version of the Language Server Protocol and addition of new features from LSP

  • Performance and resource consumption

  • Ease integration in clients

  • Improve features for binding between XML and grammar

  • Improve formatting options

  • Fix bugs. See a list of issues for missing features and bugs to fix in LSP4XML. 

Project Leads
Interested Parties


  • Red Hat Inc.
  • Pivotal
  • Liferay Inc.

Interested projects: Here are some clients consuming this XML Language Server:

Initial Contribution

The initial contribution is a functional implementation, known as LSP4XML, currently hosted on GitHub, with active contributors: The code provides the necessary code to support known XML features like XML completion, quick fixes, validation (basic and based on XML Schema/DTD)

The copyright mostly belongs to Angelo Zerr and Red Hat, contributions that were made by non-Red Hat contributors were done on files that show the Copyright and license headers, without any concern from contributors. So it's assumed that all contributors have contributed approving the EPL 2 license.

The namespace/package of the project would be org.eclipse.lemminx.


Source Repository Type