A free online OpenAPI editor that respects your spec — and your privacy

OASForge is a browser-based OpenAPI editor with a live, dark-themed Swagger UI preview beside the code. You write YAML (or JSON) on the left and watch the rendered documentation update on the right — with validation, context-aware autocomplete and one-click structure insertion doing the heavy lifting.

Built for writing specs, not fighting them

• Insert menu — add a complete CRUD resource, an endpoint, a parameter, a request body, a response, a schema or a security scheme with one click. Everything lands in the right section with correct indentation, and the placeholder name arrives pre-selected so you can type the real one immediately.
• Context-aware autocomplete — press Ctrl+Space and get only the keys that are valid at the cursor: operation keys inside get:, schema keywords under schema:, media types under content:, and live $ref targets read from your own document.
• Inline rule menu — put the cursor on a property and a small “+ rule” pill offers the validation keywords that fit its type (minLength, pattern, enum, required, …).
• Find and filter — Ctrl+F searches the code; the preview has a full-text operation search across paths, parameters, schema properties and status codes.

Every keystroke stays on your machine

There is no backend and no account. Documents live in your browser’s local storage, snapshots included. That makes OASForge safe for specs you cannot paste into cloud tools — internal APIs, pre-release contracts, client work. It even runs from a single offline HTML file with no web server at all.

All OpenAPI versions, one editor

OASForge understands Swagger 2.0 (with a one-click converter to OpenAPI 3), OpenAPI 3.0, 3.1 and 3.2 — and its validation messages are version-aware, so a key that is valid in 3.1 but unknown in 3.0 is explained rather than just flagged.