A breaking change is a change to a component, such as a server, that could break a dependent component, such as a client, for example deleting an endpoint. When working with OpenAPI, breaking changes can be caught by monitoring changes to the specification.

To detect breaking changes between two specs run oasdiff with the breaking command:

oasdiff breaking https://raw.githubusercontent.com/Tufin/oasdiff/main/data/openapi-test1.yaml https://raw.githubusercontent.com/Tufin/oasdiff/main/data/openapi-test3.yaml

Oasdiff detects over 100 kinds of breaking changes categorized into two levels:

• ERR - Errors are definite breaking changes which should be avoided
• WARN - Warnings are potential breaking changes which developers should be aware of, but cannot be confirmed programmatically

To see the full list of breaking changes that are supported by oasdiff, run:

oasdiff checks --severity warn,error

A common way to use oasdiff is by running it as a step the CI/CD pipeline to detect breaking changes.
In order to prevent breaking changes, oasdiff can be configured to return an error if any breaking change is found:

• To exit with return code 1 when any ERR-level breaking changes are found, add the --fail-on ERR flag.
• To exit with return code 1 when any breaking changes are found, WARN-level or ERR-level, add the --fail-on WARN flag.

By default, breaking changes are displayed as human-readable text with color.
You can specify the --format flag to output breaking changes in other formats: json, yaml, githubactions or junit.
An additional format singleline displays each breaking change on a single line, this can be useful to prepare ignore files

When outputting breaking changes to a Unix terminal, oasdiff automatically adds colors with ANSI color escape sequences.
If output is piped into another process or redirected to a file, oasdiff disables color.
To control color manually, use the --color flag with always or never.

When a new API is introduced, you may want to allow developers to change its behavior without triggering a breaking change error.
You can define an endpoint's stability level with the x-stability-level extension.
There are four stability levels: draft->alpha->beta->stable.
APIs with the levels draft or alpha can be changed freely without triggering a breaking change error.
Stability level may be increased, but not decreased, like this: draft->alpha->beta->stable.
APIs with no stability level will trigger breaking changes errors upon relevant change.
APIs with no stability level can be changed to any stability level.

Example:

/api/test:
 post:
  x-stability-level: "alpha"

Before deleting an endpoint, it is recommended to give consumers a heads-up in the form of "deprecation". Oasdiff allows you to deprecate APIs gracefully without triggering a breaking-change error.

Sometimes, you want to allow certain breaking changes, for example, when your spec and service are out-of-sync and you need to correct the spec.
Oasdiff allows you define breaking changes that you want to ignore in a configuration file.
You can specify the configuration file name in the oasdiff command-line with the --warn-ignore flag for WARNINGS or the --err-ignore flag for ERRORS.
Each line in the configuration file should contain two parts:

1. Method and path (the first field in the line beginning with slash) to ignore a change to an endpoint, or the keyword 'components' to ignore a change in components
2. Description of the breaking change

For example:

GET /api/{domain}/{project}/badges/security-score removed the success response with the status '200'

Or, for a component change:

components removed the schema 'rules'

The required parts may appear in any order, in lower or upper case, and the configuration line may contain additional text, like this:

 - 12.01.2023 In GET /api/{domain}/{project}/badges/security-score we removed the success response with the status '200'
 - 31.10.2023 Removed the schema 'network-policies' from components

The configuration files can be of any text type, e.g., Markdown, so you can use them to document breaking changes and other important changes.

The new Breaking Changes method support rules for enum changes using the x-extensible-enum extension.
This method allows adding new entries to enums used in responses which is very usable in many cases but requires clients to support a fallback to default logic when they receive an unknown value. x-extensible-enum was introduced by Zalando and picked up by the OpenAPI community. Technically, it could be replaced with anyOf classical enum but the x-extensible-enum is a more explicit way to do it.
In most cases the x-extensible-enum is similar to enum values, except it allows adding new entries in messages sent to the client (responses or callbacks). If you don't use the x-extensible-enum in your OpenAPI specifications, nothing changes for you, but if you do, oasdiff will identify breaking changes related to x-extensible-enum parameters and properties.

Oasdiff supports a few optional breaking changes checks which can be added with the --include-checks flag. For example:

oasdiff breaking data/openapi-test1.yaml data/openapi-test3.yaml --include-checks response-non-success-status-removed

To see a list of optional checks, run:

oasdiff checks --required false

To display changes in other languages, use the --lang flag.
Currently English and Russian are supported.
Please improve oasdiff by adding your own language.

If you encounter a change that isn't considered breaking by oasdiff you may:

1. Check if the change is already available as an optional breaking changes check.
2. Add a custom check

Here are some examples of breaking and non-breaking changes that oasdiff supports.
This document is automatically generated from oasdiff unit tests.

• no checks for context instead of schema for request parameters
• no checks for callbacks