Packet Format

Overview

Every UDP packet delivered by ShredStream.com is exactly 1203 bytes and contains a single Merkle data shred (variant 0xA5). ShredStream.com delivers data shreds only -- no FEC or coding shreds are included in the stream.

Each shred carries a portion of a Solana slot's entry data. Shreds arrive with sequential indexes within each slot, starting from 0. To reconstruct the full block data for a slot, collect all its shreds, order them by index, and concatenate the payloads.

Memory Layout

┌──────────────────────────────────────────────┐
│  0x00  Signature (64 bytes)                  │
├──────────────────────────────────────────────┤
│  0x40  Shred Variant (1 byte) = 0xA5        │
├──────────────────────────────────────────────┤
│  0x41  Slot (8 bytes, LE u64)               │
├──────────────────────────────────────────────┤
│  0x49  Index (4 bytes, LE u32)              │
├──────────────────────────────────────────────┤
│  0x4D  Version (2 bytes, LE u16)            │
├──────────────────────────────────────────────┤
│  0x4F  FEC Set Index (4 bytes, LE u32)      │
├──────────────────────────────────────────────┤
│  0x53  Parent Offset (2 bytes, LE u16)      │
│  0x55  Flags (1 byte)                        │
│  0x56  Size (2 bytes, LE u16)               │
├──────────────────────────────────────────────┤
│  0x58  Payload (up to 1115 bytes)           │
├──────────────────────────────────────────────┤
│  Merkle proof + chained root (variable)      │
└──────────────────────────────────────────────┘
Total: 1203 bytes

Complete Offset Table

Offset	Size	Field	Type	Description
0x00	64	Signature	bytes	Ed25519 signature over the shred contents
0x40	1	Shred Variant	u8	Always 0xA5 (Merkle data shred)
0x41	8	Slot	u64 LE	Slot number this shred belongs to
0x49	4	Index	u32 LE	Shred index within the slot (sequential)
0x4D	2	Version	u16 LE	Shred version
0x4F	4	FEC Set Index	u32 LE	FEC set this shred belongs to
0x53	2	Parent Offset	u16 LE	Offset to the parent slot
0x55	1	Flags	u8	Boundary flags: DATA_COMPLETE = 0x40, LAST_IN_SLOT = 0x20
0x56	2	Size	u16 LE	Payload size in bytes
0x58	variable	Payload	bytes	Actual entry data
after payload	variable	Merkle Proof	bytes	Merkle proof nodes + chained root

Constants

Constant	Value	Notes
SHRED_MAX_SIZE	1203 bytes	Fixed size of every UDP packet
DATA_HEADER_SIZE	88 bytes (0x58)	Total header size before the payload
MAX_PAYLOAD_SIZE	1115 bytes	Theoretical maximum payload; actual size varies because the Merkle proof at the end of the packet consumes some of the remaining space

Flags Byte

The flags byte at offset 0x55 signals shred boundaries using a bitmask:

Flag	Value	Meaning
DATA_COMPLETE	0x40	This is the last data shred in the current FEC set / entry batch
LAST_IN_SLOT	0x20	This is the last data shred in the entire slot

When LAST_IN_SLOT is set, you know the slot is complete and you can reassemble all collected shreds for that slot into the full block data.

Important Notes

• Data shreds only. ShredStream.com delivers Merkle data shreds (variant 0xA5). You will not receive FEC/coding shreds.

• Sequential indexes. Within each slot, shred indexes start at 0 and increment sequentially. Missing an index means a shred was lost in transit.

• Payload size. The Size field at offset 0x56 tells you the actual number of payload bytes. This may be less than the full payload area because the Merkle proof occupies space at the end of the packet.

• Merkle proof. The trailing Merkle proof and chained root are used for cryptographic verification. For most data-extraction use cases, you can safely ignore them and read only the payload bytes indicated by the Size field.

• Signature. The 64-byte Ed25519 signature at the start of the packet is produced by the block leader and can be used to verify shred authenticity.