A GitHub Action to quickly validate JSON and YAML files in a repository

This action comes pre-packaged with two different common JSON and YAML validators:

• JSON validation with ajv - The fastest NodeJS JSON validator
• YAML validation with yaml-schema-validator

If you have a repository containing JSON or YAML files and want to validate them extremely quickly, this action is for you!

You can provide schemas to check against, or just validate the syntax of the files. This comes very handy when you want to ensure that your JSON and YAML files are valid before committing them to your repository, especially from pull requests.

This Action is also extremely fast ⚡. It uses fdir under the hood for directory crawling and file globbing when looking for JSON and YAML files. This Action can crawl through a million files in under a second and validate those files in just a few more.

Here is a quick example of how to install this action in any workflow:

# checkout the repository (required for this Action to work)
- uses: actions/checkout@v4

# validate JSON and YAML files
- name: json-yaml-validate
  uses: GrantBirki/json-yaml-validate@vX.X.X # <--- replace with the latest version

Here are some basic usage examples for this Action

name: json-yaml-validate 
on:
  push:
    branches:
      - main
  pull_request:
  workflow_dispatch:

permissions:
  contents: read

jobs:
  json-yaml-validate:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: json-yaml-validate
        id: json-yaml-validate
        uses: GrantBirki/json-yaml-validate@vX.X.X # replace with the latest version

Here is a usage example in the context of a pull request with comment mode enabled:

name: json-yaml-validate 
on:
  push:
    branches:
      - main
  pull_request:
  workflow_dispatch:

permissions:
  contents: read
  pull-requests: write # enable write permissions for pull request comments

jobs:
  json-yaml-validate:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: json-yaml-validate
        id: json-yaml-validate
        uses: GrantBirki/json-yaml-validate@vX.X.X # replace with the latest version
        with:
          comment: "true" # enable comment mode

The resulting comment will look like this:

This Action also supports schema validation for both JSON and YAML files.

References docs for both JSON and YAML schema validation can be found at the links below:

• JSON Schema Validation Docs
• YAML Schema Validation Docs - Additional docs here

Note: JSON files and YAML files use two separate libraries for schema validation

Assuming the following repository structure:

/
├── schemas/
│   ├── schema.yml
│   └── schema.json
├── data/
│   ├── test.json
│   └── test.yml
└── ...

Here is an example of how to use this feature:

# checkout the repository
- uses: actions/checkout@v4

- name: json-yaml-validate
  uses: GrantBirki/json-yaml-validate@vX.X.X # replace with the latest version
  with:
    yaml_schema: schemas/schema.yml # validate YAML files against the schema
    json_schema: schemas/schema.json # validate JSON files against the schema

When this Action workflow runs, it will validate all JSON and YAML files in the repository against the schema files in the schemas/ directory.

If you want to only validate files in the data/ directory, you could set the base_dir input to data/

For validating a .json file with a .json schema

{
  "foo": 1,
  "bar": "abc"
}

{
  "type": "object",
  "properties": {
    "foo": {
      "type": "integer"
    },
    "bar": {
      "type": "string"
    }
  },
  "required": [
    "foo"
  ],
  "additionalProperties": false
}

Details on the fields seen in the schema above:

• type - the type of the value, can be one of string, number, integer, boolean, array, object, null
• required - an array of strings, each of which is a property name that is required
• additionalProperties - a boolean value that determines if additional properties are allowed in the object

You can also use custom regex formats in your JSON schema. This is useful for validating specific formats of strings. This section describes how you can use custom regex formats with this Action.

Here is an example JSON schema that uses custom regex formats:

For this example, assume that the JSON schema's file path is ./schemas/custom_with_regex.json from the root of the repository

{
  "type": "object",
  "properties": {
    "lowercase_char_property": {
      "type": "string",
      "format": "lowercase_char"
    },
    "lowercase_alphanumeric_property": {
      "type": "string",
      "format": "lowercase_alphanumeric"
    }
  },
  "required": ["lowercase_char_property", "lowercase_alphanumeric_property"],
  "additionalProperties": false
}

Here is an example file that we are going to validate against the schema above:

For this example, assume that the JSON file's file path is config/valid.json from the root of the repository

{
  "lowercase_char_property": "valid",
  "lowercase_alphanumeric_property": "valid1"
}

Now that we have a JSON schema that uses custom regex formats and a JSON file that we want to validate against the schema, we need to provide the custom regex formats to the Action. The example workflow step below shows how to do this:

- name: json-yaml-validate
  uses: GrantBirki/json-yaml-validate@vX.X.X # replace with the latest version
  id: json-yaml-validate
  with:
    json_schema: ./schemas/custom_with_regex.json # <--- the schema file that uses custom regex formats
    ajv_custom_regexp_formats: |
      lowercase_char=^[a-z]*$
      lowercase_alphanumeric=^[a-z0-9]*$
    # ^ these are the custom regex formats used in the schema that we inject into the Action so they can be used
    files: |
      config/valid.json
    # ^ uses the example file as seen in the section above

The ajv_custom_regexp_formats input is a multi-line string that contains the custom regex formats used in the JSON schema. Each line in the string should be in the format format_name=regex_pattern. The format_name is the name of the custom regex format used in the schema, and regex_pattern is the regex pattern that the value in the JSON file must match.

For validating a .yaml file with a .yaml schema

Note: can also be .yml files, both work

The following is a sample yaml file to input into the validator schema which will be seen below:

---
person:
  name:
    first_name: monalisa
  age: 2000
  employed: true
  hobbies:
    - tennis
    - football

The schema used to validate the input file from above:

---
person:
  name:
    first_name:
      type: string
      length: # define min and max length (optional)
        min: 2
        max: 10
  age:
    type: number
    required: true # make this field required (optional)
  employed:
    type: boolean
  hobbies:
    - type: string
      enum: [football, basketball, tennis] # only accept these values (optional)

Details on the fields seen in the schema above:

• type - The type of the field (e.g. string, number, boolean, etc)
• length - The length of the field with min and max constraints
• required - Whether or not the field is required
• enums - An array of values that the field can be

There are three main ways you can go about excluding files from being validated with this Action:

• json_exclude_regex - A regex string that will be used to exclude JSON files from being validated
• yaml_exclude_regex - A regex string that will be used to exclude YAML files from being validated
• exclude_file - best way to exclude files - A file that contains a list of files to exclude from being validated in gitignore format

It should be strongly noted that both json_exclude_regex and yaml_exclude_regex options get unwieldy very quickly and are not recommended. The exclude_file option is the best way to exclude files from being validated. Especially if you have a large repository with many files.

Example of an exclude_file's contents:

# exclude all files in the test/ directory
test/

# exclude a yaml file at an exact path
src/cool-path/example.yaml

# exclude all json files with some glob matching
*.test.json

If the file path to your exclude_file is exclude.txt, you would set the exclude_file input to exclude.txt like so:

# checkout the repository
- uses: actions/checkout@v4

- name: json-yaml-validate
  uses: GrantBirki/json-yaml-validate@vX.X.X # replace with the latest version
  with:
    exclude_file: exclude.txt # gitignore style file that contains a list of files to exclude

Below is a very simple example of a violation warning that you might see in this Action in your Action's logs or as a comment on a pull request:

[
  {
    "file": "./test/test2.json",
    "errors": [
      {
        "path": null,
        "message": "Invalid JSON"
      }
    ]
  },
  {
    "file": "./test/test3.yaml",
    "errors": [
      {
        "path": "person.age",
        "message": "person.age must be of type String."
      }
    ]
  }
]

The example above contains two violations - one for a JSON file and one for a YAML file. Here is what each of the fields mean:

• file - The full path to file that the violation occurred in
• errors - An array of errors that occurred in the file
  • path - The path to the error in the file (if applicable) - Note: This is not the file path but rather the path place within the file that the error occurred
  • message - The error message

In the example above, the path for the JSON file is null and the message says Invalid JSON. This means that the entire file could not be parsed as JSON. Likewise, if you see null for the path and the message says Invalid YAML, this means that the entire file could not be parsed as YAML.

This section documents known issues and workarounds / fixes

If you plan on using your .gitignore file, you should always include a trailing slash when excluding a directory. For example, instead of node_modules use node_modules/. This will ensure the Action correctly detects the directory as a directory and not a file.