The development started over 2 years ago as part of the Network Automation, the Intelligent Service Composition project. It was supporting the model driven composition of resources/services/products.


Development of a tool as generic as possible
  • not bound to a particular schema/profile
  • no particular type of post-processing (orchestrator)
  • limited to TOSCA YAML profile
  • Java language


Ensure that a (set of) TOSCA template(s)is conform to a correctly defined type system
  • avoid errors at more expensive later processing stages
  • pre-requisite to further processing: UI rendeing, persistence

Generate an intermediate form that could facilitate further processing

  • accommodate extensions to the standard and checks pertinent to these extensions

The checker

Validate YAML document
  • supports streaming documents (multiple documents within one file), YAML anchors, etc
  • currently uses the snakeyaml library
Syntax check
  • two pre-defined grammars, 1.0 and 1.1, with the possibility of handling a mix of documents version wise
  • other versions/variants can be added ‘on the fly’, identified through the tosca_definitions_version entry
  • accept the short forms
  • declare the short forms within the grammar
  • builds a canonical form from which the shorts forms are eliminated (so further processing steps do not need to handle them)
  • grammar written in yaml
  • easy to maintain/modify
  • processed through a modified version of the kwalify library
  • type hierarchy checks for all constructs
  • valid re-definitions: from relatively simple (properties) to rather complicated (interface opearations)
  • valid type references: all referenced types are pre-declared (as super-types, as valid source types, etc)
  • templates respect their respective type definition
  • example: check type of interface operation inputs
  • other references: capabilities and requirements in substitution mappings
  • data checks: assignments match the type specification, function argument compatibility (for built-in functions), constraints matching

Process the entire document tree specified through import statements

  • pluggable document locator/loader
  • pluggable handlers at syntax check (pre/post validation)
  • pluggable checks based on document location
  • a new construct (new grammar) can be subject to new semantic checks plugged without checker code being re-built.


Error reporting
  • Differs depending on the stages
  • Document position indication during parsing
  • Document path and rule during syntax check
  • Document path during checking
  • No explicit representation of TOSCA constructs, offers a query interface with results being exposed as common Java types: maps, lists, ..
  • domain specific (TOSCA constructs) navigation built through a proxy based approach on top of above representation


  • simple API that allows access to any stage of the checker
  • One can build an in-memory representation of a TOSCA document and skip the yaml parsing.
  • Re-usable Catalog (hierarchical Catalogs)
  • One or more documents can be processed and the resulting Catalog be preserved and used for later processing of other documents using the previous catalog as base catalog
  • basic command line interface
  • stateful REST service layer on top of checker API
  • a schema (document with type specifications) can be submitted and be referenced (imports) from subsequently submitted templates


A tiny framework for additional processing
  • one basic implementation of a JavaScript post-processor where the Catalog and topology graph are exposed to javascript scripts implementing business validation rules