Monaco YAML

YAML language plugin for the Monaco Editor. It provides the following features when editing YAML files:

• Code completion, based on JSON schemas or by looking at similar objects in the same file
• Hovers, based on JSON schemas
• Validation: Syntax errors and schema validation
• Formatting using Prettier
• Document Symbols
• Automatically load remote schema files (by enabling DiagnosticsOptions.enableSchemaRequest)
• Links from JSON references.
• Links and hover effects from YAML anchors.
• Code folding.

Schemas can also be provided by configuration. See here for the API that the plugin offers to configure the YAML language support.

• Installation
• Usage
• Examples
• API
  • configureMonacoYaml(monaco, options?)
    • Arguments
    • Options
    • Returns
• FAQ
  • Does this work with the Monaco UMD bundle?
  • Does this work with Monaco Editor from a CDN?
  • Does this work with @monaco-editor/loader or @monaco-editor/react?
  • Is the web worker necessary?
  • Does it work without a bundler?
  • How do I integrate monaco-yaml with a framework? (Angular, React, Vue, etc.)
  • Does monaco-yaml work with create-react-app?
  • Why doesn’t it work with Vite?
  • Why isn’t monaco-yaml working? Official Monaco language extensions do work.
  • Using Monaco webpack loader plugin
  • Why is syntax highlighting not working?
  • Why does it try to download my schema even when I provided one as an object?
• Contributing
• Credits
• License

npm install monaco-yaml

Before implementing monaco-yaml, or even Monaco editor, it’s recommended to learn the basic concepts of Monaco editor.

To configure monaco-yaml, call configureMonacoYaml.

import * as monaco from 'monaco-editor'
import { configureMonacoYaml } from 'monaco-yaml'

configureMonacoYaml(monaco, {
  enableSchemaRequest: true,
  schemas: [
    {
      // If YAML file is opened matching this glob
      fileMatch: ['**/.prettierrc.*'],
      // Then this schema will be downloaded from the internet and used.
      uri: 'https://json.schemastore.org/prettierrc.json'
    },
    {
      // If YAML file is opened matching this glob
      fileMatch: ['**/person.yaml'],
      // The following schema will be applied
      schema: {
        type: 'object',
        properties: {
          name: {
            type: 'string',
            description: 'The person’s display name'
          },
          age: {
            type: 'integer',
            description: 'How old is the person in years?'
          },
          occupation: {
            enum: ['Delivery person', 'Software engineer', 'Astronaut']
          }
        }
      },
      // And the URI will be linked to as the source.
      uri: 'https://github.com/remcohaszing/monaco-yaml#usage'
    }
  ]
})

const prettierc = monaco.editor.createModel(
  'singleQuote: true\nproseWrap: always\nsemi: yes\n',
  undefined,
  monaco.Uri.parse('file:///.prettierrc.yaml')
)

monaco.editor.createModel(
  'name: John Doe\nage: 42\noccupation: Pirate\n',
  undefined,
  monaco.Uri.parse('file:///person.yaml')
)

monaco.editor.create(document.getElementById('editor'), {
  automaticLayout: true,
  model: prettierc
})

Also make sure to register the web worker. When using Webpack 5, this looks like the code below. Other bundlers may use a different syntax, but the idea is the same. Languages you don’t used can be omitted.

window.MonacoEnvironment = {
  getWorker(moduleId, label) {
    switch (label) {
      case 'editorWorkerService':
        return new Worker(new URL('monaco-editor/esm/vs/editor/editor.worker', import.meta.url))
      case 'css':
      case 'less':
      case 'scss':
        return new Worker(new URL('monaco-editor/esm/vs/language/css/css.worker', import.meta.url))
      case 'handlebars':
      case 'html':
      case 'razor':
        return new Worker(
          new URL('monaco-editor/esm/vs/language/html/html.worker', import.meta.url)
        )
      case 'json':
        return new Worker(
          new URL('monaco-editor/esm/vs/language/json/json.worker', import.meta.url)
        )
      case 'javascript':
      case 'typescript':
        return new Worker(
          new URL('monaco-editor/esm/vs/language/typescript/ts.worker', import.meta.url)
        )
      case 'yaml':
        return new Worker(new URL('monaco-yaml/yaml.worker', import.meta.url))
      default:
        throw new Error(`Unknown label ${label}`)
    }
  }
}

A demo is available on monaco-yaml.js.org.

Some usage examples can be found in the examples directory.

monaco-yaml has the following exports:

Configure monaco-yaml.

Note: There may only be one configured instance of monaco-yaml at a time.

• monaco (object): The Monaco editor module. Typically you get this by importing monaco-editor. Third party integrations often expose it as the global monaco variable instead.
• options (object): Options to configure monaco-yaml.

• completion (boolean): If set, enable schema based autocompletion. (Default: true)
• customTags (string[]): A list of custom tags. (Default: [])
• enableSchemaRequest (boolean): If set, the schema service will load schema content on-demand. (Default: false)
• format (boolean): Prettier from the bundle. (Default: true)
• hover (boolean): If set, enable hover typs based the JSON schema. (Default: true)
• isKubernetes (boolean): If true, a different diffing algorithm is used to generate error messages. (Default: false)
• schemas (object[]): A list of known schemas and/or associations of schemas to file names. (Default: [])
• validate (boolean): based validation. (Default: true)
• yamlVersion ('1.1' | '1.2'): The YAML version to use for parsing. (Default: 1,2)

An object that can be used to dispose or update monaco-yaml.

Yes, starting from version 5.0.0

Yes, starting from version 5.0.0

Yes, starting from version 5.0.0

Yes. The web worker provides the core functionality of monaco-yaml.

No. monaco-yaml uses dependencies from node_modules, so they can be deduped and your bundle size is decreased. This comes at the cost of not being able to use it without a bundler.

monaco-yaml only uses the Monaco Editor. It’s not tied to a framework, all that’s needed is a DOM node to attach the Monaco Editor to. See the Monaco Editor examples for examples on how to integrate Monaco Editor in your project, then configure monaco-yaml as described above.

Yes, but you’ll have to eject. See #92 (comment) for details.

Some users have experienced the following error when using Vite:

Uncaught (in promise) Error: Unexpected usage
  at EditorSimpleWorker.loadForeignModule (editorSimpleWorker.js)
  at webWorker.js

As a workaround, create a file named yaml.worker.js in your own project with the following contents:

import 'monaco-yaml/yaml.worker.js'

Then in your Monaco environment getWorker function, reference this file instead of referencing monaco-yaml/yaml.worker.js directly:

import YamlWorker from './yaml.worker.js?worker'

window.MonacoEnvironment = {
  getWorker(moduleId, label) {
    switch (label) {
      // Handle other cases
      case 'yaml':
        return new YamlWorker()
      default:
        throw new Error(`Unknown label ${label}`)
    }
  }
}

This is most likely due to the fact that monaco-yaml is using a different instance of the monaco-editor package than you are. This is something you’ll want to avoid regardless of monaco-editor, because it means your bundle is significantly larger than it needs to be. This is likely caused by one of the following issues:

• A code splitting misconfiguration

  To solve this, try inspecting your bundle using for example webpack-bundle-analyzer. If monaco-editor is in there twice, this is the issue. It’s up to you to solve this, as it’s project-specific.

• You’re using a package which imports monaco-editor for you, but it’s using a different version.

  You can find out why the monaco-editor is installed using npm ls monaco-editor or yarn why monaco-editor. It should exist only once, but it’s ok if it’s deduped.

  You may be able to solve this by deleting your node_modules folder and package-lock.json or yarn.lock, then running npm install or yarn install respectively.

If you’re using monaco webpack plugin, then instead of the above code, you can extend the plugin’s configuration. Extend your webpack.config.js file with the following:

import { MonacoWebpackPlugin } from 'monaco-editor-webpack-plugin'

export default {
  // ...the rest of your webpack configuration...
  plugins: [
    new MonacoWebpackPlugin({
      languages: ['yaml'],
      customLanguages: [
        {
          label: 'yaml',
          entry: 'monaco-yaml',
          worker: {
            id: 'monaco-yaml/yamlWorker',
            entry: 'monaco-yaml/yaml.worker'
          }
        }
      ]
    })
  ]
}

You can also refer to the example of a complete project.

Syntax highlighting is provided by Monaco editor itself, not by monaco-yaml. If you use a build tool to filter languages or features, make sure to include the yaml language. If you import Monaco editor from monaco-editor/esm/vs/editor/editor.api.js and cherry-pick features manually, make sure to also import monaco-editor/esm/vs/basic-languages/yaml/yaml.contribution.js. If you use monaco-editor-core, make sure to import monaco-languages/release/esm/yaml/yaml.contribution.js.

You may have provided a schema configured like this:

{
  uri: "http://example.com",
  fileMatch: ["file_name.yml"],
  schema: {
    $schema: "http://json-schema.org/draft-07/schema#",
    $id: "http://example.com",
    title: "placeholder title",
    description: "placeholder description",
    type: "object",
    properties: {
      name: {
        description: "name property description",
        type: "string",
      },
    },
    required: ["name"],
  },
}

And would be surprised to see the error:

Unable to load schema from '<http://example.com>': Failed to fetch.

It happens because plugin uses schema URI not only as the URL to download the schema from, but also to determine the schema name. To fix this, change the uri parameter to http://example.com/schema-name.json.

Please see our contributing guidelines

Originally @kpdecker forked this repository from monaco-json by @microsoft and rewrote it to work with yaml-language-server instead. Later the repository maintenance was taken over by @pengx17. Eventually the repository was tranferred to the account of @remcohaszing, who is currently maintaining this repository with the help of @fleon and @yazaabed.

The heavy processing is done in yaml-language-server, best known for being the backbone for vscode-yaml. This repository provides a thin layer to add functionality provided by yaml-language-server into monaco-editor.

MIT