Programmatic access to all data in your asana system.
Asana API is a free Documents & Productivity API that requires apiKey authentication, is served over HTTPS and supports CORS, so it can be called from the browser.
Learn the basics of Asana's developer platform
Details from developers.asana.com.

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The Asana API is provided by Asana Docs (developers.asana.com). Learn the basics of Asana's developer platform
Yes. The Asana API is listed in the Documents & Productivity category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Asana API uses apiKey authentication, so you need to register for credentials before making requests.
Yes. The Asana API supports CORS, so front-end JavaScript can call it directly.
Yes. The Asana API is served over HTTPS, so it's safe to use in production.