oasdiff/oasdiff: OpenAPI Diff and Breaking Changes

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Command-line tool to compare and detect breaking changes in OpenAPI specs.

Run it locally, in CI via the GitHub Action, or use the hosted PR review workflow at oasdiff.com to approve or reject each change with a CI commit status.

Get started in 30 seconds

No install needed — try it with Docker against two sample specs:

docker run --rm -t tufin/oasdiff changelog \
  https://raw.githubusercontent.com/oasdiff/oasdiff/main/data/openapi-test1.yaml \
  https://raw.githubusercontent.com/oasdiff/oasdiff/main/data/openapi-test5.yaml

That prints a human-readable changelog of the changes that can affect API consumers, breaking and non-breaking. Swap changelog for breaking to see only the changes that break existing API clients, or diff for the full machine-readable diff of the API definition, including documentation-only edits.

Installation

Install with Go

go install github.com/oasdiff/oasdiff@latest

Install on macOS with Brew

brew install oasdiff

Install on macOS and Linux using curl

The install.sh script downloads the latest oasdiff binary into /usr/local/bin:

curl -fsSL https://raw.githubusercontent.com/oasdiff/oasdiff/main/install.sh | sh

To pin a specific version, set the version env var:

curl -fsSL https://raw.githubusercontent.com/oasdiff/oasdiff/main/install.sh | version=1.11.7 sh

Install with asdf

https://github.com/oasdiff/asdf-oasdiff

Download a binary

Documentation

Grouped by what you're trying to do. New to oasdiff? Start with Commands.

Commands

• diff — full diff of the API definition, including documentation-only edits (output: html, json, markdown, markup, text, or yaml — default yaml)
• summary — high-level count of changes between two specs (built on the diff engine; same shared options)
• breaking — only the changes that break existing API clients
• changelog — changes that can affect API consumers, breaking or not, in human-readable form
• breaking-files — check a list of changed specs against their versions in a git ref, one comparison per spec; used by the pre-commit hook
• flatten — replace allOf schemas with a merged equivalent
• upgrade — canonicalize an OpenAPI 3.0 spec to the latest 3.x
• validate — check a single spec for per-RFC violations (invalid types, missing required fields, bad regex, unresolved $refs)
• checks changelog — list the rules breaking and changelog use to classify changes (customize them)
• checks validate — list the rules validate reports
• checks changelog coverage — list every possible edit of an OpenAPI document with the checks that cover it
• schema — print a JSON Schema for the breaking/changelog json output
• git-diff-driver — run as a git external diff driver so git log --patch renders an OpenAPI changelog inline

Inputs

• Git revisions — compare against a branch, tag, or commit
• Local files, http/s URLs, YAML or JSON — all handled transparently

Comparison

• Endpoint matching — handles renamed path parameters and duplicate endpoints
• Nullability changes — the three equivalent nullable forms and when changing them is breaking
• Compare APIs split across multiple files — e.g. an API gateway with one spec per service
• Check many independent specs — one comparison per spec, rather than merging them as composed mode does
• Filter endpoints — narrow the diff to a subset of endpoints

Normalization

• Merge allOf schemas
• Merge common (path-level) parameters
• Path prefix modification — strip or add a prefix so a moved API still matches
• Case-insensitive header comparison — treat Content-Type and content-type as the same header

API lifecycle

• Deprecate APIs and parameters
• API stability levels (draft / alpha / beta / stable)
• Version bumps — report a breaking change released without a major version bump

Filtering changes

• Exclude certain kinds of changes — e.g. ignore description-only edits
• Track OpenAPI extensions — opt in to reporting changes in x-* fields
• Exclude specific extension names — when extensions are tracked, skip ones you don't care about

Output

• Customize HTML and Markdown changelog templates
• Add OpenAPI-extension attributes to changelog entries
• Source location tracking
• Change fingerprints — stable IDs across commits
• Error reporting
• Localization: en, ru, pt-br, es

How to run

• Docker
• Configuration file
• Embed in a Go program
• GitHub Action for CI — and oasdiff.com for teams, which adds a per-change PR comment with approve/reject and commit-status checks
• MCP server — call oasdiff from an AI assistant (Claude, Cursor, ...) via the hosted server at https://api.oasdiff.com/mcp

Reference

• OpenAPI 3.1 and 3.2 support — what's supported
• Security: control external $ref loading to prevent SSRF
• Usage examples — recipes for common scenarios
• Contributing

Demo

Credits

Feedback