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Python library to check Swagger Spec backward compatibility

Project description PyPi version Supported Python versions



swagger-spec-compatibility is a Yelp maintained library that provides tools to automatically detect the safety of Swagger/OpenAPI 2.0 specification changes with respect to backwards compatibility.

swagger-spec-compatibility aims to give developers confidence that their spec changes are safe and that clients built with previous versions of the Swagger spec can continue to communicate correctly.


More documentation is available at

How to Install

# to install the latest released version
$ pip install swagger-spec-compatiblity

# to install the latest master [from Github]
$ pip install git+

Example Usage

The commands below assume that the library is already installed

$ swagger_spec_compatibility -h

usage: swagger_spec_compatibility [-h]
                              [-r {MIS-E001,MIS-E002,REQ-E001,REQ-E002,REQ-E003,RES-E001,RES-E002,RES-E003} [{MIS-E001,MIS-E002,REQ-E001,REQ-E002,REQ-E003,RES-E001,RES-E002,RES-E003} ...]]
                              {explain,run} ...

Tool for the identification of backward incompatible changes between two swagger specs.

The tool provides the following level of results:
- WARNING: the Swagger specs are technically compatible but the are likely to break known Swagger implementations
- ERROR: new Swagger spec does introduce a breaking change respect the old implementation

positional arguments:
  {explain,run}         help for sub-command
    explain             explain selected rules
    run                 run backward compatibility detection

optional arguments:
  -h, --help            show this help message and exit
  -r {MIS-E001,MIS-E002,REQ-E001,REQ-E002,REQ-E003,RES-E001,RES-E002,RES-E003} [{MIS-E001,MIS-E002,REQ-E001,REQ-E002,REQ-E003,RES-E001,RES-E002,RES-E003} ...], --rules {MIS-E001,MIS-E002,REQ-E001,REQ-E002,REQ-E003,RES-E001,RES-E002,RES-E003} [{MIS-E001,MIS-E002,REQ-E001,REQ-E002,REQ-E003,RES-E001,RES-E002,RES-E003} ...]
                        Rules to apply for compatibility detection. (default:
                        ['MIS-E001', 'MIS-E002', 'REQ-E001', 'REQ-E002',
                        'REQ-E003', 'RES-E001', 'RES-E002', 'RES-E003'])
$ swagger_spec_compatibility explain -r=REQ-E001 -r=REQ-E002 explain
Rules explanation
[REQ-E001] Added Required Property in Request contract:
    Adding a required property to an object used in requests leads client request to fail if the property is not present.
[REQ-E002] Removed Enum value from Request contract:
    Removing an enum value from a request parameter is backward incompatible as a previously valid request will not be
    valid. This happens because a request containing the removed enum value, valid according to the "old" Swagger spec, is
    not valid according to the new specs.
$ old_spec_path=docs/source/rules/examples/REQ-E001/old.yaml
$ new_spec_path=docs/source/rules/examples/REQ-E001/new.yaml

# Run with all the registered rules
$ swagger_spec_compatibility run ${old_spec_path} ${new_spec_path}
ERROR rules:
    [REQ-E001] Added Required Property in Request contract : #/paths//endpoint/post/parameters/0/schema
$ echo $?

# Run with a subset of registered rules
$ swagger_spec_compatibility -r=MIS-E001 -r=MIS-E002 run ${old_spec_path} ${new_spec_path}
$ echo $?


Code is documented using Sphinx.

virtualenv is recommended to keep dependencies and libraries isolated.


# Initialize your dev environment
$ make minimal

# Ensure that you have activated the virtualenvironment
$ source ./venv/bin/activate

Tip: If you have aactivator installed the virtual environment will be automatically activated

How to define a new compatibility rule

Use the following steps to define a new rule:

  1. Define a new rule class in swagger_spec_compatibility/rules/

# Example of the file content  (assume that the file will be named
class RuleClassName(BaseRule):
    description = ''
    error_code = 'ERROR_CODE'
    error_level = Level.LEVEL
    rule_type = RuleType.TYPE
    short_name = ''

    def validate(cls, left_spec, right_spec):
        # type: (Spec, Spec) -> typing.Iterable[ValidationMessage]
        # Implement here your logic
        raise NotImplemented()

 # Please make sure that:
 #  * `description` and `short_name` are reasonably explicative to support `swagger_spec_compatibility explain` command
 #  * `error_code` has REQ- prefix for `RuleType.REQUEST_CONTRACT`, RES- for `RuleType.RESPONSE_CONTRACT` and MIS- for `RuleType.MISCELLANEOUS`
  1. Add tests to ensure that your rule behaves as expected (tests in tests/rules/

  1. Add documentation for the defined rule in docs/source/rules/ERROR_CODE.rst. Try to be consistent with the style of the others documentation pages

  2. Add example of a Swagger spec change that triggers the rule in docs/source/rules/examples/ERROR_CODE.rst. Ensure to define a file that will make explicit the backward incompatible change through the usage of a bravado client (check the other testers for examples). NOTE: The testers are executed by automated tests, this is intended to ensure that documentation is in sync with the codebase.

  3. [Optional] Add integration tests to ensure that no regressions will be introduced and/or to validate edge cases of the new rule. Integration tests are defined as follow: case-<incremental number>-<number of expected reports>-reports-<short description> directory with two files: old.yaml and new.yaml. The two files represent two versions of the swagger specs that need to be checked for backward compatibility.


  1. Fork it ( )

  2. Create your feature branch (git checkout -b my-new-feature)

  3. Add your modifications

  4. Commit your changes (git commit -m "Add some feature")

  5. Push to the branch (git push origin my-new-feature)

  6. Create new Pull Request


Copyright 2019 Yelp, Inc.

Swagger Spec Compatibility is licensed with a Apache License 2.0.

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