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Generate UUIDs.
UUID Generator API is a free Test Data API that requires no API key, is served over HTTPS and does not support CORS, so it should be called from a server.
Free UUID and GUID generator API. No key needed. Generate v1, v3, v4, v5, v6, v7, v8, nil and max UUIDs as JSON or plain text, in bulk, and decode or validate any UUID.
Details from uuidtools.com.

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The UUID Generator API is provided by UUIDTools.com (uuidtools.com). Free UUID and GUID generator API. No key needed. Generate v1, v3, v4, v5, v6, v7, v8, nil and max UUIDs as JSON or plain text, in bulk, and decode or validate any UUID.
Yes. The UUID Generator API is listed in the Test Data 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 UUID Generator API requires no authentication, so you can start making requests without signing up.
Not directly. The UUID Generator API does not allow CORS, so call it from a server, serverless function or proxy instead of front-end JavaScript.
Yes. The UUID Generator API is served over HTTPS, so it's safe to use in production.