Yaml Extension provides deeper integration with YAML (YAML Ain't Markup Language), including linting yaml documents and validating against known JSON schemas, including Kubernetes resources.


Yaml Extension requires some additional tools to be installed on your Mac:

  • Node.js 16 and NPM 7 or newer
  • Node.js is used to run redhat-developer/yaml-language-server
  • NPM is used to install the server during extension installation
  • Older versions of Node.js and NPM should still work, but newer versions are advised.

To install the current stable version of Node, click the "Recommended for Most Users" button to begin the download. When that's done, double-click the .pkg installer to begin installation.

Node version managers — If you use something like nvm or fnm, make sure it is configured inside your profile file (.zprofile or .bash_profile) instead of your "rc" file (.zshrc or .bashrc). See Environment Variables for more. You may also have to restart Nova for any changes to take effect.


Yaml Extension runs any time you open a local project with YAML files in it, it automatically lints all open files, then reports errors and warnings in Nova's Issues sidebar and the editor gutter:

JSON schemas

This extension works by associating YAML files with JSON schemas based on well-known names and open-source schemas that are available online. For example, .circleci/config.yml or .github/workflows/**.yml have known schemas which we can validate those files against.

To see all available schemas, visit

Custom schema configuration

You can also configure custom schema mappings in .nova/Configuration.json manually, e.g.

  "yaml.schemas": {
    "": "my-custom-lerna.yaml"
    "": ["*-action.yml"],
    "../some/relative/path.json": [

More information →

Where the key is a URL or path to the your JSON schema, and the value is a glob pattern or array of patterns of files to match against.

Currently, Nova doesn't support this type of configuration so it cannot be done in the Project → Project Settings... UI.

Inline Schema Comments

You can add this special comment at the top of your schema file to tell the Yaml Extension which schema to use:

# yaml-language-server: $schema=<urlToTheSchema>

or with a relative path:

# yaml-language-server: $schema=../relative/path/to/schema

or with an absolute path:

# yaml-language-server: $schema=/absolute/path/to/schema

More Information →

Custom tags

YAML tags let you programatically control the parsing of values in YAML files. For example, a tag could be used to unpack a secret:

passwordKey: !secret database.password

Yaml Extension needs to know about these tags so it can help with suggestions and error messages. You can define these globally or per-project inside of Nova.

Note: global and per-project custom tags are not merged. If you have global tags you will need to duplicate them if you want to use per-project tags.

Each line of the configuration should be a separate tag you want to add. It can optionally have a type, which Yaml Extension will check the value of.

The type can be either scalar, mapping or sequence, for more information, look here.

Global custom tags

To set global custom-tags, go to ExtensionsExtension Library.... Then navigate to YAML and then to the Preferences tab.

Per-project custom tags

To set per-project, navigate to your project settings by clicking your project name in the top left. Then go to YAML in the side bar and configure Custom tags there.

Example custom tags

!secret scalar
!automobile mapping
!peopleList sequence

Under the hood

Yaml Extension runs the redhat-developer/yaml-language-server Language Server which pulls down associations from and filters out the ones that aren't YAML. When you open a YAML file, it sees if it is associated with a schema and if it is, it downloads the schema to do hover/validation/completions.


You can opt-in to Kubernetes support on a per-project basis. You need to manually configure your project's settings in .nova/Configuration.json to tell the Yaml Language Server which files you want it to consider to be Kubernetes ones.

To help with this, there is the Extensions → YAML → Setup Kubernetes Schemas command to bootstrap the process. It will open your local .nova/Configuration.json and attempt to add a placeholder schema mapping towards the latest supported Kubernetes JSON schema.

Warning This command covers lots of cases for your existing (or non-existing project configuration) but it will erase any previous yaml.schemas that you may have set. If you have custom schemas setup, I'd recommend running the command in a blank project and manually merging the JSON back together again.

The placeholder is setup to match suffixes based on the kubectl api-resources output, but you can customise this as much as you'd like. You can re-run the command to reset back to the placeholder.

Under the hood there is one generic Kubernetes schema which decides the structure based on what apiVersion and kind are set to. So you don't need to worry about mapping different schemas to different files.

This schema is from yannh/kubernetes-json-schema and the command picks the highest version that is known to work with the Language Server.

The placeholder will match files like:

Hopefully a future version of this extension will parse out the apiVersion and kind values and validate files dynamically based on them, but this currently isn't possible. This is being tracked here.


Advanced configuration

The underlying Language Server provides more configuration which you can use by editing the .nova/Configuration.json file in your project. Details of these options can be found here.


Yaml Extension requires these Nova permissions:


  • to associate YAML files with json schemas
  • to download individual json schemas to validate against
  • to download the language server when you first install or subsequently update the extension.


  • to determine where Node.js is installed
  • to install the language server with NPM
  • to run the language server which provides most of the features


  • to read in YAML files so they can be validated
  • to write back to files when applying completions
  • to install the language server in extension storage (~/Library/Application Support/Nova/Extensions/robb-j.yaml)
  • when using the Setup Kubernetes Schemas command

This information is based on my experience setting up the language server (which I didn't write). If you find it is doing something not described above please fill out an Issue, I want this information to be as accurate and informative as possible.


  1. Select the Extensions → Extension Library... menu item
  2. Search for "Yaml"
  3. Click the Install Button


If believe something isn't working, you can try restarting the yaml server. Select the Extensions → YAML → Restart Server menu item

If things seem really wrong, check the extension console to find out more information. Select the Extensions → Show Extension Console menu item, then pick the Yaml source.

If you see any errors in that log that aren't like Error: Invalid parameter: registrations, or the stack trace below that, please fill out an Issue.

Known issues

  • Indentation on completions can be incorrect


This repo does not provide the YAML syntax highlighting in Nova, those are provided by Panic.



  • Remove debug logs slowing down the extension




Thanks to Patrick Fricano!



  • Document advanced configuration


  • Re-add option to toggle document validation



  • Remove unused validate and format configuration that didn't actually do anything.
  • Tidy up the README and explain things better.
  • Update Setup Kubernetes Schemas command to use kubernetes keyword that automatically hooks in to the Language Server's Kubernetes support. More info →
  • Upgrade yaml-language-server to 1.10.0 from 1.8.0, see yaml-language-server CHANGELOG for more.



  • Add an error message when installing the language server fails.
  • Upgrade yaml-language-server to 1.8.0 from 1.7.0, see yaml-language-server CHANGELOG for more.



  • Improve the experience when the extension cannot find Node.js / NPM. There's a new notification to tell you what happened and it links to a new readme section to help out.
  • All compiled code is now Open Source, if you fancy diving in to see what Yaml Extension is up to, you can
  • Upgrade yaml-language-server to 1.7.0 from 1.4.0, see yaml-language-server CHANGELOG for more.





  • Stopped creating stdin.log and stdout.log files in your projects, sorry! Please remove these files.


  • Upgrade yaml-language-server to 0.22.0, it was previously 0.19.2, see yaml-language-server CHANGELOG for more.
  • IMPORTANT by-default support for Kubernetes schemas has been dropped. I hope to be able to add this again in the future but it is not possible with current versions of the yaml server and Nova. See the to see how to configure this now.
  • New command Setup Kubernetes Schemas to help configure Kubernetes schema in the new way, as per above.
  • Lots of internals of the server have been refactored, but this shouldn't be a noticeable change.



  • Fix extension preferences, they weren't initially synchronised between Nova and the YAML server.
  • Upgraded yaml-language-server to 0.19.2, it was 0.18.0. See the Changelog
  • Downgrade the npm-shrinkwrap.json back to v1 for better compatibility.



  • New configuration options, you can configure how Yaml Extension works in the extension's "Preferences" tab.
  • Toggle formatting
  • Toggle validation
  • Toggle hover tooltips
  • Toggle completions
  • Custom tags support
  • For more see "Custom tags" in the readme






Initial release