VSCode JSON Language Server

The JSON Language server provides language-specific smarts for editing, validating and understanding JSON documents. It runs as a separate executable and implements the language server protocol to be connected by any code editor or IDE.

Capabilities

Server capabilities

The JSON language server supports requests on documents of language id json and jsonc.

• json documents are parsed and validated following the JSON specification.
• jsonc documents additionally accept single line (//) and multi-line comments (/* ... */) and accepts trailing commas. JSONC is a VSCode specific file format, intended for VSCode configuration files, without any aspirations to define a new common file format.

The server implements the following capabilities of the language server protocol:

• Code completion for JSON properties and values based on the document's JSON schema or based on existing properties and values used at other places in the document. JSON schemas are configured through the server configuration options.
• Hover for values based on descriptions in the document's JSON schema.
• Document Symbols for quick navigation to properties in the document.
• Document Colors for showing color decorators on values representing colors and Color Presentation for color presentation information to support color pickers. The location of colors is defined by the document's JSON schema. All values marked with "format": "color-hex" (VSCode specific, non-standard JSON Schema extension) are considered color values. The supported color formats are #rgb[a] and #rrggbb[aa].
• Code Formatting supporting ranges and formatting the whole document.
• Diagnostics (Validation) are pushed for all open documents
  • syntax errors
  • structural validation based on the document's JSON schema.

In order to load JSON schemas, the JSON server uses NodeJS http and fs modules. For all other features, the JSON server only relies on the documents and settings provided by the client through the LSP.

Client requirements:

The JSON language server expects the client to only send requests and notifications for documents of language id json and jsonc.

The JSON language server has the following dependencies on the client's capabilities:

• Code completion requires that the client capability has snippetSupport. If not supported by the client, the server will not offer the completion capability.
• Formatting support requires the client to support dynamicRegistration for rangeFormatting. If not supported by the client, the server will not offer the format capability.

Configuration

Settings

Clients may send a workspace/didChangeConfiguration notification to notify the server of settings changes. The server supports the following settings:

• http

  • proxy: The URL of the proxy server to use when fetching schema. When undefined or empty, no proxy is used.
  • proxyStrictSSL: Whether the proxy server certificate should be verified against the list of supplied CAs.

• json

  • format
    • enable: Whether the server should register the formatting support. This option is only applicable if the client supports dynamicRegistration for rangeFormatting
    • schema: Configures association of file names to schema URL or schemas and/or associations of schema URL to schema content.
      • fileMatch: an array or file names or paths (separated by /). * can be used as a wildcard.
      • url: The URL of the schema, optional when also a schema is provided.
      • schema: The schema content.

	{
        "http": {
            "proxy": "",
            "proxyStrictSSL": true
        },
        "json": {
            "format": {
                "enable": true
            },
            "schemas": [
                {
                    "fileMatch": [
                        "foo.json",
                        "*.superfoo.json"
                    ],
                    "url": "http://json.schemastore.org/foo",
                    "schema": {
                    	"type": "array"
                    }
                }
            ]
        }
    }

Schema configuration and custom schema content delivery

JSON schemas are essential for code assist, hovers, color decorators to work and are required for structural validation.

To find the schema for a given JSON document, the server uses the following mechanisms:

• JSON documents can define the schema URL using a $schema property
• The settings define a schema association based on the documents URL. Settings can either associate a schema URL to a file or path pattern, and they can directly provide a schema.
• Additionally, schema associations can also be provided by a custom 'schemaAssociations' configuration call.

Schemas are identified by URLs. To load the content of a schema, the JSON language server tries to load from that URL or path. The following URL schemas are supported:

• http, https: Loaded using NodeJS's HTTP support. Proxies can be configured through the settings.
• file: Loaded using NodeJS's fs support.
• vscode: Loaded by an LSP call to the client.

Schema associations notification

In addition to the settings, schemas associations can also be provided through a notification from the client to the server. This notification is a JSON language server specific, non-standardized, extension to the LSP.

Notification:

• method: 'json/schemaAssociations'
• params: ISchemaAssociations defined as follows

interface ISchemaAssociations {
	[pattern: string]: string[];
}

• keys: a file names or file path (separated by /). * can be used as a wildcard.
• values: An array of schema URLs

Schema content request

The schema content for schema URLs that start with vscode:// will be requested from the client through an LSP request. This request is a JSON language server specific, non-standardized, extension to the LSP.

Request:

• method: 'vscode/content'
• params: string - The schema URL to request. The server will only ask for URLs that start with vscode://
• response: string - The content of the schema with the given URL

Schema content change notification

When the client is aware that a schema content has changed, it will notify the server through a notification. This notification is a JSON language server specific, non-standardized, extension to the LSP. The server will, as a response, clear the schema content from the cache and reload the schema content when required again.

Notification:

• method: 'json/schemaContent'
• params: string the URL of the schema that has changed.

Try

The JSON language server is shipped with Visual Studio Code as part of the built-in VSCode extension json-language-features. The server is started when the first JSON file is opened. The VSCode JSON documentation for detailed information on the user experience and has more information on how to configure the language support.

Integrate

If you plan to integrate the JSON language server into an editor and IDE, check out this page if there's already an LSP client integration available.

You can also launch the language server as a command and connect to it. For that, install the json-language-server npm module:

npm install -g json-language-server

Start the language server with the json-language-server command. Use a command line argument to specify the prefered communication channel:

json-language-server --node-ipc
json-language-server --stdio
json-language-server --socket=<port>

To connect to the server from NodeJS, see Remy Suen's great write-up on how to communicate with the server through the available communication channels.

Participate

The source code of the JSON language server can be found VSCode repository at extensions/json-language-features/server. File issues and pull requests in the VSCode GitHub Issues. See the document How to Contribute on how to build and run from source.

Most of the functionality of the server is located in libraries:

• jsonc-parser contains the JSON parser and scanner.
• vscode-json-languageservice contains the implementation of all features as a re-usable library.
• vscode-languageserver-node contains the implementation of language server for NodeJS.

Help on any of these projects is very welcome.

Please see also our Code of Conduct.

License

Copyright (c) Microsoft Corporation. All rights reserved.

Licensed under the MIT License.