Aspen

Aspen is a free macOS app for testing REST APIs locally, with no login and no data saved to external servers. Its AI companion, Alfred, generates data models, OpenAPI specs and integration code from your requests.

You enter the request parameters, send them and get results in under a second, all running on your own machine. The zero-trust approach means nothing is stored outside your Mac, which the makers position as the main difference from Postman or Insomnia.

Collections let you organize, import, export and share API requests with teammates, including importing files from Postman. Alfred speeds up integration work by turning responses into typed models and code you can paste into a project.