Plugin Schemas

Plugins define their desired form of their config using draft 4 of the JSON Schema specification. The schema for a plugin should be stored schema attribute of the plugin class. The schema is used for several things including:

  • Validating the config format matches what is expected

  • Set defaults in the config that user did not provide

  • Generating a form for the webui config editor

You can run the test in the suite to test the validity of your plugin’s schema. The error messages it produces may help you fix your schema if you are having trouble. Note that this doesn’t check the schema validates what you want, just that it is a valid json schema.

The following list of keywords is not exhaustive, just a general primer, as well as some FlexGet specific notes. The JSON schema spec should be referred to for more details, or if a keyword is not covered here. Take not that our schemas will be defined as python objects equivalent to parsed JSON. The full list of valid keywords can be found in section 5 of the validaton spec.



The type keyword specifies what primitive data type a given item in the config should have. It can either be a single type, or a list of types. The type keyword should be specified in almost every schema, even when other keywords are included which might make it redundant, as it is used to select which branch should be chosen to show errors when the config can take multiple forms. The types in JSON schema are slightly different than their python counterparts. Here are the valid options, along with the python types they map to:

JSON Schema type

Python type
















This keyword is used to validate the content of a list (‘array’ in json schema terms.) Its value should be a schema that each item in the list matches.

The following example describes a list of strings:

{"type": "array", "items": {"type": "string"}}


This keyword is used to validate the values in a dictionary. It should be a dictionary mapping from key name, to schema which validates the value for that key.

The following example describes a dictionary with two keys, ‘a’, and ‘b’, both of which must be integers (additionalProperties will be explained below):

    "type": "object",
    "properties": {
        "a": {"type": "integer"},
        "b": {"type": "integer"}
    "additionalProperties": False


By default, JSON schema will allow any keys which are not defined in the properties dictionary without validation. To disallow extra keys, use the {"additionalProperties": False} form, as in the above example. This should be used in almost every schema which defines the properties keyword. The other use for this keyword is if you want to allow a dictionary with any keys, but still require the values to match a schema.

The following example allows a dictionary with any keys, as long as the values are strings:

    "type": "object",
    "additionalProperties": {"type": "string"}

oneOf and anyOf

These keywords are used when the config could take more than one format. The value should be a list of schemas one of which, or any of which must match, depending on the keyword used.

The following schema will allow either a boolean or an integer:

{"oneOf": [{"type": "boolean"}, {"type": "integer"}]}


The format keyword is used to make sure a string follows a specific format. Here are the format validators included with FlexGet, along with what they validate:


email addresses


FlexGet quality, e.g. 720p hdtv


FlexGet quality requirements specifier, e.g. 720p-1080p hdtv+


A text representation of a time interval, e.g. 3 hours, 10 minutes Intervals in this format can be parsed to a datetime.timedelta object using the utility function


valid regular expression


an existing file on the local filesystem


an existing directory on the local filesystem (if path contains Jinja, only validates path exists before first Jinja component of path)

The following schema checks for valid regex:

{"type": "string", "format": "regex"}


This keyword is used to reference a schema defined somewhere else. The most common use of this keyword will be to allow a plugin to take other plugins within their configuration. It takes the form of an URI reference. The fragment part should be a JSON pointer to a section of the referenced document. If only a fragment portion of an URI is specified, the base document is assumed to be the current schema.

The following schema allows a dictionary with keys equal to plugin names (which have input phase handlers,) and values equal to the configuration required for that plugin. We don’t actually define the validation keywords here, we are just referencing an already built schema which has been registered by some other plugin or component of FlexGet:

{"$ref": "/schema/plugins?phase=input"}


This keyword does not affect validation, it is merely used to define parts of your schema that may get re-used in more than one place. It should be in the form of a dictionary mapping arbitrary names to a schema.

The following schema defines a definition called posNumber, and references it from two places within the schema:

    "type": "object",
    "properties": {
        "numberA": {"$ref": "#/definitions/posNumber"},
        "numberB": {"$ref": "#/definitions/posNumber"}
    "additionalProperties": False,
    "definitions": {
        "posNumber": {"type": "number", "minimum": 0}

The $ref used in this example included a fragment part of an URI only, so it references this schema, and drills down into it with a JSON pointer.

title and description

The title and description keywords are not used during validation at all. If provided, they will be used to display more information to the user in the configuration editor.


The default keyword is not used during validation either. It will be used to fill in default values for properties in the config that the user has not provided. This will be done automatically before the parsed config is passed to the plugin.


The not keyword will allow you to negate a specific schema. This is especially useful when wanting to create mutually exclusive properties or groups:

    "type": "object",
    "properties": {
        "this": {"type": "string"},
        "that": {"type": "string"}
    "not": {
        "required": ["this", "that"]
    "error_not": "Can not use both 'this' and 'that'

Another more complex example:

    "type": "object",
    "properties": {
        "this": {"type": "string"},
        "that": {"type": "string"},
        "those": {"type": "string"}
    "not": {
        "anyOf": [
            "required": ["this", "that"],
            "required": ["this", "those"],
            "required": ["that", "those"]
    "error_not": "Can only use one of 'this', 'that' or 'those'


dependencies are used to link a property to one or more other property, raising a validation error if not all dependencies have been met:

   "type": "object",
   "properties": {
       "this": {"type": "string"},
       "that": {"type": "string"},
       "another" {"type": "string"}
   "dependencies": {
       "this": ["that"]