IconVault's OpenAPI Viewer turns a raw OpenAPI or Swagger spec into a readable API reference. Paste or upload your spec in JSON or YAML and browse every endpoint grouped by tag, with HTTP methods, summaries, parameters, request bodies and responses laid out clearly, plus search to jump to the operation you need. A built-in sample spec lets you explore before loading your own.

It is free with no signup, and your spec is only visualized: no requests are executed and nothing is uploaded. The honest limitation: this is a viewer, not a try-it-out client, so you cannot send live requests from here, use a dedicated API client for that.