OpenAPI vs Swagger: What's the Difference?

If you’ve seen both terms used seemingly interchangeably, that’s because for a while they mostly were the same thing. But “Swagger” and “OpenAPI” point at different things today, and mixing them up makes it harder to search for the right tooling.

The short version

The Swagger Specification was the original name for the spec format that describes a REST API’s endpoints, parameters, and responses in JSON or YAML. In 2015, SmartBear donated the spec to the newly formed OpenAPI Initiative (under the Linux Foundation), and it was renamed the OpenAPI Specification starting with version 3.0. The spec kept evolving under the new name — OpenAPI is the current, actively maintained standard.

Swagger didn’t disappear — it now refers to SmartBear’s suite of tools built around that spec: Swagger UI (renders a spec as interactive docs), Swagger Editor, and Swagger Codegen. So “Swagger” today means a set of tools, while “OpenAPI” means the format those tools (and many others) consume.

Why the confusion persists

A few reasons this naming mix-up is still common:

• Version numbering carried over. Swagger 2.0 became OpenAPI 3.0, not OpenAPI 2.0 — there’s no OpenAPI 2.0, which trips people up when they see “Swagger 2.0” specs still in production and assume it’s an older OpenAPI version rather than the pre-rename spec.
• File names didn’t change. Plenty of teams still name their spec file swagger.json or swagger.yaml out of habit, even though its openapi: 3.0.0 or openapi: 3.1.0 field marks it as an OpenAPI document, not a Swagger 2.0 one.
• “Swagger UI” is genuinely the most-searched viewer, so “Swagger” gets used as a generic stand-in for “API docs tool” the way “Google” gets used as a stand-in for “search.”

Does the difference matter practically?

Mostly for compatibility. Swagger 2.0 and OpenAPI 3.x aren’t wire-compatible — a 2.0 document needs conversion (via swagger2openapi or similar) before a 3.x-native tool can render it correctly. If your spec already declares openapi: 3.0.x or openapi: 3.1.x, you’re on the current standard and any modern viewer, GetMan included, will read it directly. See OpenAPI 3.1 vs 3.0 if you’re deciding which 3.x version to target.

Picking a viewer

Once your spec is a proper OpenAPI 3.x document, the choice of renderer is separate from the spec-vs-tool question above. If you’re currently using Swagger UI specifically and evaluating alternatives, the Swagger UI alternative page walks through the tradeoffs. For a general read on what tools like GetMan need from a spec, the docs cover the setup end to end.