GUID (Microsoft term) and UUID (standard) are the same: 128‑bit global unique identifiers used to identify objects, sessions, devices, files, etc. Common uses include database primary keys, distributed system IDs, API request tracing, and file identifiers.
v1: time + node (may include MAC — privacy risk).
v3 / v5: namespace + name (deterministic; v3 uses MD5, v5 uses SHA‑1).
v4: random (most common).
v7: time‑ordered (better for DB indexing).
v8: experimental/extension.
Formats: hyphenated (8‑4‑4‑4‑12), no hyphens, braces { }, parentheses ( ). Encodings: raw string, HEX, Base64, Base64URL, byte array, URN. Export files (TXT/CSV/JSON) follow current settings.
Collision probability is extremely low; for typical applications you can treat UUIDs as effectively unique.
Random v4 UUIDs can fragment indexes and hurt write performance. For primary keys prefer time‑ordered UUIDs (e.g., v7) or other strategies to reduce index fragmentation.
All GUIDs are generated locally in your browser and are not uploaded. If using v1, avoid exposing device MAC by using a random node or choose v4/v7.