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Q & A Developer · September 11, 2026

Are UUIDs guaranteed to be unique?

No — UUIDs are probabilistically unique, not absolutely unique. For UUIDv4 the birthday-paradox math: you’d need to generate approximately 2.7 × 10^18 UUIDs before there’s a 50% chance of a single collision. In practice this means: don’t worry about UUIDv4 collisions. For UUIDv1 (time-based), collisions are prevented by combining timestamp + MAC address + counter. Both are safe for real-world use — including primary keys, session IDs, and distributed system identifiers. Generate them with the UUID generator.

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What Is a JWT?
JWT (JSON Web Token) is the dominant format for API authentication, OAuth access tokens, and stateless session management. Three base64-encoded segments carry the header, claims, and signature — anyone can read them, but only the key holder can produce a valid token.
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