Yet another Guid library:-) Create Uuid v1, v3, v5, v6, v7, v8MsSql, v8SHA256, v8SHA512, convert between v1 and v6, convert between v7 and v8MsSql, get Guid info, create NEWSEQUENTIALID (ms sql), create/reverse Xor Guid, create/reverse numeric Guid, create/reverse incremented Guid.
Version 7 Guid's generated by GuidPhantom are monotonic and encoded as:
Bits
48 Unix timestamp milliseconds
4 0x7 (version)
12 Random data / counter
2 0x2 (variant)
6 Random data / counter
56 Random data
Counter start as 4bit random data.
If timestamp does not change, the counter start to increment + 1.
If the counter overflows, the timestamp is incremented + 1 and the counter is extended with 1 bit (up to max 18bits).
Counter bits are reduced gradually if on the edge/reset to 4bits when time catches up.
Dynamic counter bits balance maximal randomness during low volume generation and not going too far into the future during high volume generation.
NOTE: monotony breaks if clock goes back in time.
NOTE: monotony is per process.
var v1 = GuidKit.CreateVersion1();
var v3 = GuidKit.CreateVersion3(new Guid("d2f2f0fe-cbf8-4dc8-9ecb-eedd066dc105"), "Test42");
var v5 = GuidKit.CreateVersion5(new Guid("d2f2f0fe-cbf8-4dc8-9ecb-eedd066dc105"), "Test42");
var v6 = GuidKit.CreateVersion6();
var v7 = GuidKit.CreateVersion7();
var v8mssql = GuidKit.CreateVersion8MsSql();
var v8sha256 = GuidKit.CreateVersion8SHA256(new Guid("d2f2f0fe-cbf8-4dc8-9ecb-eedd066dc105"), "Test42");
var v8sha512 = GuidKit.CreateVersion8SHA512(new Guid("d2f2f0fe-cbf8-4dc8-9ecb-eedd066dc105"), "Test42");
var v6_converted = v1.ConvertVersion1To6();
var v1_converted = v6.ConvertVersion6To1();
var v7_converted = v8mssql.ConvertVersion8MsSqlTo7();
var v8mssql_converted = v7.ConvertVersion7To8MsSql();
var nsi = GuidKit.CreateNEWSEQUENTIALID();
var vv = nsi.GetVariantAndVersion();
var info = nsi.GetGuidInfo();
var xor = GuidKit.CreateXorGuid(new Guid("d2f2f0fe-cbf8-4dc8-9ecb-eedd066dc105"), new Guid("7e00d52e-8496-4239-92fc-4d59a0cde28d"));
var b = xor.ReverseXorGuid(new Guid("d2f2f0fe-cbf8-4dc8-9ecb-eedd066dc105"));
var num = GuidKit.CreateNumericGuid(42);
int num42 = num.ReverseNumericGuid();
var inc = GuidKit.CreateIncrementedGuid(new Guid("d2f2f0fe-cbf8-4dc8-9ecb-eedd066dc105"), 42);
int inc42 = inc.ReverseIncrementedGuid(new Guid("d2f2f0fe-cbf8-4dc8-9ecb-eedd066dc105"));
Also has sql scripts for ms sql server to create Guid v3, v5, v7, v8mssql and convert between v7 and v8mssql. Uses variable counter, from 4 to 12bits.
v8mssql: Similar to Version 7, but bits reordered to make it ordered as uniqueidentifier in Ms Sql Server. Ms Sql Server's uniqueidentifier has strange rules for ordering, so only NEWSEQUENTIALID (non-standard) and v8mssql will be properly ordered. It is possible to use Version 7 stored as a binary(16) for proper ordering, if stored as big endian. Can either use big endian byte array's directly from client, or send Guid/uniqueidentifier from the client and convert to byte array in sql, then need to use eg. dbo.uuid_swap_endian(...), to make it big endian.
Analysis:
GuidKit.CreateVersion7() 019d33c0-6a33-7e03-8cb9-6a24c0e84f80 019d33c0-6a33-7fd4-b819-a0c2a1e455e6 019d33c0-6a34-71fb-9e10-684a1d50e0f5 019d33c0-6a34-7266-b223-efb917ec2c3f 019d33c0-6a34-729c-ac00-53b7c29e3b53 019d33c0-6a34-7369-8e29-c45d40b8ddce 019d33c0-6a34-73a7-b1ae-ea7a91255842 019d33c0-6a34-741e-8724-ea8d1b0a93bc 019d33c0-6a34-74ae-99be-8632e7b20eea 019d33c0-6a34-752f-a2ff-53e4b9978e27 Guid.CreateVersion7() 019d33c0-6a42-7e91-81a2-105dec7df176 019d33c0-6a42-74c2-a949-00ecfea193a1 019d33c0-6a42-72f9-b157-90b8869235dd 019d33c0-6a42-7967-ac17-06dbbfef8795 019d33c0-6a42-7418-bfe4-56e1d18a1f7e 019d33c0-6a42-7cab-b57c-4e0b0951d4e5 019d33c0-6a42-7f1a-8b27-2fa46539de67 019d33c0-6a42-7a06-9a69-f5465c8ebfc8 019d33c0-6a42-733a-862e-75a5615b6fd4 019d33c0-6a42-7fa5-95c0-0184bdf3b600 Uuid.NewSequential() 019d33c0-6a42-7610-91cf-ec81a655d219 019d33c0-6a42-7611-bfb0-7b2d2e3c2ca2 019d33c0-6a42-7612-b0fa-6c238463e879 019d33c0-6a42-7613-919b-0035ef46ba3e 019d33c0-6a42-7614-9686-48c1207da8ef 019d33c0-6a42-7615-bd19-8a2aa0cc1cae 019d33c0-6a42-7616-afa5-7363b3dc8fe4 019d33c0-6a42-7617-b40f-9a12e735b24f 019d33c0-6a42-7618-b9a7-7c17e057127c 019d33c0-6a42-7619-8290-de35eef23179
Lets break it down:
The rand_a field is the key: UUID v7 structure: [48-bit ms timestamp]-[ver][12-bit rand_a]-[var][62-bit rand_b]
When multiple UUIDs are generated within the same millisecond, monotonicity depends entirely on what goes in rand_a.
GuidKit.CreateVersion7() — random monotonic ✅
The rand_a bits increment each call:
019d33c0-6a34-71fb → 7[1fb] 019d33c0-6a34-7266 → 7[266] 019d33c0-6a34-729c → 7[29c] 019d33c0-6a34-7369 → 7[369] ← counter
Uuid.NewSequential() — strictly monotonic ✅
Even more obvious — it's just incrementing by 1:
019d33c0-6a42-7610 019d33c0-6a42-7611 019d33c0-6a42-7612 ← +1 counter
Guid.CreateVersion7() — NOT monotonic ❌
All same millisecond (6a42), but rand_a is random each time:
019d33c0-6a42-7e91 019d33c0-6a42-74c2 019d33c0-6a42-72f9 ← pure random 019d33c0-6a42-7967
RFC 9562 (the UUID v7 spec) permits but does not require a monotonic counter in rand_a. It offers three methods for same-millisecond ordering:
- Method 1 Fixed-length counter (Uuid.NewSequential())
- Method 2 Monotonic random (increment by random amount - GuidKit.CreateVersion7())
- Method 3 Re-seed randomly each time (what .NET does) .NET's Guid.CreateVersion7() deliberately chose Method 3 — it re-randomizes rand_a every call. This is spec-compliant, but means same-millisecond UUIDs have no guaranteed sort order. It was a conscious tradeoff: simpler implementation, no shared counter state, but no sub-ms monotonicity. If you need database-friendly sortable UUIDs (e.g. for clustered index inserts), GuidKit or Uuid.NewSequential() are the better choices.
References:
- https://zendesk.engineering/how-probable-are-collisions-with-ulids-monotonic-option-d604d3ed2de
- https://github.com/mareek/UUIDNext
- https://github.com/LiosK/uuidv7
- https://math.stackexchange.com/questions/4697032/threshold-for-the-number-of-uuids-generated-per-millisecond-at-which-the-colli
- uuid6/uuid6-ietf-draft#60