OpenAPI Editor and Visualizer

This free OpenAPI editor lets you author an OpenAPI Specification in YAML or JSON and see it as visual documentation instantly. Built-in validation flags syntax and governance issues as you write, so this OpenAPI validator catches problems before you ship.

Spec Hub extends this into a visual editor with an outline view and code snippets, and covers OpenAPI, AsyncAPI, GraphQL, Proto, and Smithy in one place. You can generate a Postman Collection from your Specification and keep it in sync as the collection changes. You can define custom governance rules and use the Postman CLI to lint your spec in your CI pipelines. You can also sync specs to git and generate a full SDK straight from the finished spec.

Your spec generates a Collection you can run and test directly, staying in two-way sync as the spec evolves.

Spec Hub lets you update the collection once the spec is updated — this way your collections always stay in sync with the specification.

Yes — you can start with a collection and enrich it with type information. The collection can then be converted into a specification and kept in sync, so Postman supports two-way sync between collections and specifications.

OpenAPI validation errors often point at a symptom rather than the root cause — a missing required field upstream can surface as an unrelated error several lines later.

OpenAPI covers REST; AsyncAPI covers event-driven and WebSocket APIs. Spec Hub supports both in one place if your API needs both.