Defines a common protocol for language servers.

Language Server Protocol

Note: A blog covering the background and mechanics of the protocol has been added to the Visual Studio Code site. Additionally today Red Hat, Eclipse Che and others announced support for the protocol.

The Language Server protocol is used between a tool (the client) and a language smartness provider (the server) to integrate features like auto complete, goto definition, find all references and alike into the tool. The following diagram illustrates the communication between a tool and the language server.

Interaction diagram

The language server maintains semantic information about a program implemented in a particular language.

  • When the user opens a document in the tool, it notifies the language server that the document was opened and that the truth of the document is now maintained by the tool in a memory buffer.
  • When the user edits the document, the server is notified of the changes and updates the program's semantic information.
  • As the user makes changes the language server analyses the document and notifies the tool with any errors and warnings (diagnostics) that it finds.
  • When the user requests to go to the definition of a symbol, the client sends a definition request to the server. The server responds with the URI of the document and a range inside that document. Based on this information the tool opens the corresponding document at the position where the symbol is defined.
  • When the user closes the document, a didClose notification is sent, informing the language server that the truth of the file is now on the file system.

The communication between the Editor/IDE host and the Language Server uses JSON RPC v2.0. The protocol supports servers with different capabilities. The first request sent from the Editor/IDE to the language server informs the server about the supported language features.

The first version of the protocol is based on experiences we gained while integrating OmniSharp and the TypeScript Server into VS Code. See the history section for a brief history on how the protocol evolved.


If you are interested in fixing issues like typos or contributing directly to the protocol specification you can either file an issue or provide a pull request containing the changes to the file.

When proposing an extension to the specification, then please refer to an implementation of the proposed changes in a language server. This will help us in understanding the particular use case.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact with any additional questions or comments.

The Language Server Protocol

The file specifies the language server protocol.


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