UK Public Tenders by Trade
Live open UK public sector tenders by trade from Find a Tender and Contracts Finder (OGL v3.0)
US federal spending data.
USAspending.gov API is a free Government API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
Details from api.usaspending.gov.

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Live open UK public sector tenders by trade from Find a Tender and Contracts Finder (OGL v3.0)
US congressional stock-trade disclosures and the President's OGE reports, linked to each filing
Point-in-time amendment history for UK law
The USAspending.gov API is provided by USAspending API (api.usaspending.gov).
Yes. The USAspending.gov API is listed in the Government 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 USAspending.gov API requires no authentication, so you can start making requests without signing up.
CORS support for the USAspending.gov API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The USAspending.gov API is served over HTTPS, so it's safe to use in production.