oasdiff vs Zally

oasdiff compares OpenAPI specifications, produces changelogs, and identifies breaking changes before release. It supports OpenAPI 3.0, 3.1, and 3.2, and detects 755 distinct breaking and non-breaking API changes. The CLI is available through Homebrew, a shell installer, Docker, and pre-built Linux, macOS, and Windows binaries. Output formats include text, JSON, YAML, HTML, Markdown, and GitHub Actions annotations. Its GitHub Action compares pull-request and base-branch specifications, adding inline annotations for breaking changes. A browser diff tool compares OpenAPI or Swagger specifications without installation or sign-up. Specs and changelogs are encrypted client-side before upload, and servers retain ciphertext they cannot read. The open-source engine, CLI, and GitHub Action use the Apache 2.0 license. A free plan includes CLI diffing, changelogs, GitHub Action annotations, side-by-side review, and encrypted spec storage. Pro costs $100/month and adds approval workflow, audit trail, merge gate, and up to five reviewers across five repositories. Free review links expire after seven days; Enterprise can load specs from GitHub without uploading or storing them.

Zally is an API linter and quality assurance tool for OpenAPI specifications. It supports OpenAPI 3 and Swagger OpenAPI 2, with a RESTful API, command-line interface, and web interface. Its standard configuration checks APIs against Zalando’s RESTful Guidelines, and the project says it can also be used out of the box by others. Teams can enable or disable server-side rules, configure some existing rules, or implement their own in Kotlin. An API definition can use the x-zally-ignore extension to disable rules for that API. The web interface lists implemented rules and can lint external files and API definitions in its online editor. The project describes starting the web UI, server, and database together using Docker Compose. It also lists an unofficial Zally Maven Plugin integration. Maintained by Zalando, Zally is offered under an MIT license with an exception. Its Open source plan costs nothing.