Token cost, LLM energy, agent-hour and Proof-Adjusted Autonomy calculators by Michał Piszczek.
AI Economics Tools API is a free Machine Learning API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.

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Yes. The AI Economics Tools API is listed in the Machine Learning 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.
No. The AI Economics Tools API requires no authentication, so you can start making requests without signing up.
Yes. The AI Economics Tools API supports CORS, so front-end JavaScript can call it directly.
Yes. The AI Economics Tools API is served over HTTPS, so it's safe to use in production.