
U.S. Department of the Treasury Data.
Fed Treasury API is a free Finance API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
Detailed instructions for data scientists on how to access Fiscal Data’s datasets using APIs, including information on endpoints, filters, and more.
Details from fiscaldata.treasury.gov.

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US federal, state and local income tax calculation for 2026, with the source of every figure
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The Fed Treasury API is provided by U.S. Treasury Fiscal Data (fiscaldata.treasury.gov). Detailed instructions for data scientists on how to access Fiscal Data’s datasets using APIs, including information on endpoints, filters, and more.
Yes. The Fed Treasury API is listed in the Finance 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 Fed Treasury API requires no authentication, so you can start making requests without signing up.
CORS support for the Fed Treasury API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Fed Treasury API is served over HTTPS, so it's safe to use in production.