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TypeSystem is a comprehensive data validation library that gives you:

  • Data validation.
  • Object serialization & deserialization.
  • Form rendering.
  • Marshaling validators to/from JSON schema.
  • Tokenizing JSON or YAML to provide positional error messages.
  • 100% type annotated codebase.
  • 100% test coverage.
  • Zero hard dependencies.


Python 3.6+


$ pip3 install typesystem

If you'd like you use the form rendering using jinja2:

$ pip3 install typesystem[jinja2]

If you'd like you use the YAML tokenization using pyyaml:

$ pip3 install typesystem[pyyaml]


import typesystem

artist_schema = typesystem.Schema(
        "name": typesystem.String(max_length=100)

definitions = typesystem.Definitions()
definitions["Artist"] = artist_schema

album_schema = typesystem.Schema(
        "title": typesystem.String(max_length=100),
        "release_date": typesystem.Date(),
        "artist": typesystem.Reference("Artist", definitions=definitions)

album = album_schema.validate({
    "title": "Double Negative",
    "release_date": "2018-09-14",
    "artist": {"name": "Low"}

# {'title': 'Double Negative', 'release_date': '2018-09-14', 'artist': {'name': 'Low'}}


There are plenty of other great validation libraries for Python out there, including Marshmallow, Schematics, Voluptuous, Pydantic and many others.

TypeSystem exists because I want a data validation library that offers first-class support for:

  • Rendering validation classes into HTML forms.
  • Marshaling to/from JSON Schema.
  • Obtaining positional errors within JSON or YAML documents.

— ⭐️ —

TypeSystem is BSD licensed code. Designed & built in Brighton, England.