Runes Does Not Have a Specification

The Runes reference implementation, ord, is the normative specification of the Runes protocol.

Nothing you read here or elsewhere, aside from the code of ord, is a specification. This prose description of the runes protocol is provided as a guide to the behavior of ord, and the code of ord itself should always be consulted to confirm the correctness of any prose description.

If, due to a bug in ord, this document diverges from the actual behavior of ord and it is impractically disruptive to change ord's behavior, this document will be amended to agree with ord's actual behavior.

Users of alternative implementations do so at their own risk, and services wishing to integrate Runes are strongly encouraged to use ord itself to make Runes transactions, and to determine the state of runes, mints, and balances.

Runestones

Rune protocol messages are termed "runestones".

The Runes protocol activates on block 840,000. Runestones in earlier blocks are ignored.

Abstractly, runestones contain the following fields:

#![allow(unused)]
fn main() {
struct Runestone {
  edicts: Vec<Edict>,
  etching: Option<Etching>,
  mint: Option<RuneId>,
  pointer: Option<u32>,
}
}

Runes are created by etchings:

#![allow(unused)]
fn main() {
struct Etching {
  divisibility: Option<u8>,
  premine: Option<u128>,
  rune: Option<Rune>,
  spacers: Option<u32>,
  symbol: Option<char>,
  terms: Option<Terms>,
}
}

Which may contain mint terms:

#![allow(unused)]
fn main() {
struct Terms {
  amount: Option<u128>,
  cap: Option<u128>,
  height: (Option<u64>, Option<u64>),
  offset: (Option<u64>, Option<u64>),
}
}

Runes are transferred by edict:

#![allow(unused)]
fn main() {
struct Edict {
  id: RuneId,
  amount: u128,
  output: u32,
}
}

Rune IDs are encoded as the block height and transaction index of the transaction in which the rune was etched:

#![allow(unused)]
fn main() {
struct RuneId {
  block: u64,
  tx: u32,
}
}

Rune IDs are represented in text as BLOCK:TX.

Rune names are encoded as modified base-26 integers:

#![allow(unused)]
fn main() {
struct Rune(u128);
}

Deciphering

Runestones are deciphered from transactions with the following steps:

1. Find the first transaction output whose script pubkey begins with OP_RETURN OP_13.

2. Concatenate all following data pushes into a payload buffer.

3. Decode a sequence 128-bit LEB128 integers from the payload buffer.

4. Parse the sequence of integers into an untyped message.

5. Parse the untyped message into a runestone.

Deciphering may produce a malformed runestone, termed a cenotaph.

Locating the Runestone Output

Outputs are searched for the first script pubkey that beings with OP_RETURN OP_13. If deciphering fails, later matching outputs are not considered.

Assembling the Payload Buffer

The payload buffer is assembled by concatenating data pushes, after OP_13, in the matching script pubkey.

Data pushes are opcodes 0 through 78 inclusive. If a non-data push opcode is encountered, i.e., any opcode equal to or greater than opcode 79, the deciphered runestone is a cenotaph with no etching, mint, or edicts.

Decoding the Integer Sequence

A sequence of 128-bit integers are decoded from the payload as LEB128 varints.

LEB128 varints are encoded as sequence of bytes, each of which has the most-significant bit set, except for the last.

If a LEB128 varint contains more than 18 bytes, would overflow a u128, or is truncated, meaning that the end of the payload buffer is reached before encountering a byte with the continuation bit not set, the decoded runestone is a cenotaph with no etching, mint, or edicts.

Parsing the Message

The integer sequence is parsed into an untyped message:

#![allow(unused)]
fn main() {
struct Message {
  fields: Map<u128, Vec<u128>>,
  edicts: Vec<Edict>,
}
}

The integers are interpreted as a sequence of tag/value pairs, with duplicate tags appending their value to the field value.

If a tag with value zero is encountered, all following integers are interpreted as a series of four-integer edicts, each consisting of a rune ID block height, rune ID transaction index, amount, and output.

#![allow(unused)]
fn main() {
struct Edict {
  id: RuneId,
  amount: u128,
  output: u32,
}
}

Rune ID block heights and transaction indices in edicts are delta encoded.

Edict rune ID decoding starts with a base block height and transaction index of zero. When decoding each rune ID, first the encoded block height delta is added to the base block height. If the block height delta is zero, the next integer is a transaction index delta. If the block height delta is greater than zero, the next integer is instead an absolute transaction index.

This implies that edicts must first be sorted by rune ID before being encoded in a runestone.

For example, to encode the following edicts:

They are first sorted by block height and transaction index:

And then delta encoded as:

If an edict output is greater than the number of outputs of the transaction, an edict rune ID is encountered with block zero and nonzero transaction index, or a field is truncated, meaning a tag is encountered without a value, the decoded runestone is a cenotaph.

Note that if a cenotaph is produced here, the cenotaph is not empty, meaning that it contains the fields and edicts, which may include an etching and mint.

Parsing the Runestone

The runestone:

#![allow(unused)]
fn main() {
struct Runestone {
  edicts: Vec<Edict>,
  etching: Option<Etching>,
  mint: Option<RuneId>,
  pointer: Option<u32>,
}
}

Is parsed from the unsigned message using the following tags:

#![allow(unused)]
fn main() {
enum Tag {
  Body = 0,
  Flags = 2,
  Rune = 4,
  Premine = 6,
  Cap = 8,
  Amount = 10,
  HeightStart = 12,
  HeightEnd = 14,
  OffsetStart = 16,
  OffsetEnd = 18,
  Mint = 20,
  Pointer = 22,
  Cenotaph = 126,

  Divisibility = 1,
  Spacers = 3,
  Symbol = 5,
  Nop = 127,
}
}

Note that tags are grouped by parity, i.e., whether they are even or odd. Unrecognized odd tags are ignored. Unrecognized even tags produce a cenotaph.

All unused tags are reserved for use by the protocol, may be assigned at any time, and must not be used.

Body

The Body tag marks the end of the runestone's fields, causing all following integers to be interpreted as edicts.

Flags

The Flag field contains a bitmap of flags, whose position is 1 << FLAG_VALUE:

#![allow(unused)]
fn main() {
enum Flag {
  Etching = 0,
  Terms = 1,
  Turbo = 2,
  Cenotaph = 127,
}
}

The Etching flag marks this transaction as containing an etching.

The Terms flag marks this transaction's etching as having open mint terms.

The Turbo flag marks this transaction's etching as opting into future protocol changes. These protocol changes may increase light client validation costs, or just be highly degenerate.

The Cenotaph flag is unrecognized.

If the value of the flags field after removing recognized flags is nonzero, the runestone is a cenotaph.

Rune

The Rune field contains the name of the rune being etched. If the Etching flag is set but the Rune field is omitted, a reserved rune name is allocated.

Premine

The Premine field contains the amount of premined runes.

Cap

The Cap field contains the allowed number of mints.

Amount

The Amount field contains the amount of runes each mint transaction receives.

HeightStart and HeightEnd

The HeightStart and HeightEnd fields contain the mint's starting and ending absolute block heights, respectively. The mint is open starting in the block with height HeightStart, and closes in the block with height HeightEnd.

OffsetStart and OffsetEnd

The OffsetStart and OffsetEnd fields contain the mint's starting and ending block heights, relative to the block in which the etching is mined. The mint is open starting in the block with height OffsetStart + ETCHING_HEIGHT, and closes in the block with height OffsetEnd + ETCHING_HEIGHT.

Mint

The Mint field contains the Rune ID of the rune to be minted in this transaction.

Pointer

The Pointer field contains the index of the output to which runes unallocated by edicts should be transferred. If the Pointer field is absent, unallocated runes are transferred to the first non-OP_RETURN output.

Cenotaph

The Cenotaph field is unrecognized.

Divisibility

The Divisibility field, raised to the power of ten, is the number of subunits in a super unit of runes.

For example, the amount 1234 of different runes with divisibility 0 through 3 is displayed as follows:

Spacers

The Spacers field is a bitfield of • spacers that should be displayed between the letters of the rune's name.

The Nth field of the bitfield, starting from the least significant, determines whether or not a spacer should be displayed between the Nth and N+1th character, starting from the left of the rune's name.

For example, the rune name AAAA rendered with different spacers:

Trailing spacers are ignored.

Symbol

The Symbol field is the Unicode codepoint of the Rune's currency symbol, which should be displayed after amounts of that rune. If a rune does not have a currency symbol, the generic currency character ¤ should be used.

For example, if the Symbol is # and the divisibility is 2, the amount of 1234 units should be displayed as 12.34 #.

Nop

The Nop field is unrecognized.

Cenotaphs

Cenotaphs have the following effects:

• All runes input to a transaction containing a cenotaph are burned.

• If the runestone that produced the cenotaph contained an etching, the etched rune has supply zero and is unmintable.

• If the runestone that produced the cenotaph is a mint, the mint counts against the mint cap and the minted runes are burned.

Cenotaphs may be created if a runestone contains an unrecognized even tag, an unrecognized flag, an edict with an output number greater than the number of inputs, a rune ID with block zero and nonzero transaction index, a malformed varint, a non-datapush instruction in the runestone output script pubkey, a tag without a following value, or trailing integers not part of an edict.

Executing the Runestone

Runestones are executed in the order their transactions are included in blocks.

Etchings

A runestone may contain an etching:

#![allow(unused)]
fn main() {
struct Etching {
  divisibility: Option<u8>,
  premine: Option<u128>,
  rune: Option<Rune>,
  spacers: Option<u32>,
  symbol: Option<char>,
  terms: Option<Terms>,
}
}

rune is the name of the rune to be etched, encoded as modified base-26 integer.

Rune names consist of the letters A through Z, with the following encoding:

And so on and so on.

Rune names AAAAAAAAAAAAAAAAAAAAAAAAAAA and above are reserved.

If rune is omitted a reserved rune name is allocated as follows:

#![allow(unused)]
fn main() {
fn reserve(block: u64, tx: u32) -> Rune {
  Rune(
    6402364363415443603228541259936211926
    + (u128::from(block) << 32 | u128::from(tx))
  )
}
}

6402364363415443603228541259936211926 corresponds to the rune name AAAAAAAAAAAAAAAAAAAAAAAAAAA.

If rune is present, it must be unlocked as of the block in which the etching appears.

Initially, all rune names of length thirteen and longer, up until the first reserved rune name, are unlocked.

Runes begin unlocking in block 840,000, the block in which the runes protocol activates.

Thereafter, every 17,500 block period, the next shortest length of rune names is continuously unlocked. So, between block 840,000 and block 857,500, the twelve-character rune names are unlocked, between block 857,500 and block 875,000 the eleven character rune names are unlocked, and so on and so on, until the one-character rune names are unlocked between block 1,032,500 and block 1,050,000. See the ord codebase for the precise unlocking schedule.

To prevent front running an etching that has been broadcast but not mined, if a non-reserved rune name is being etched, the etching transaction must contain a valid commitment to the name being etched.

A commitment consists of a data push of the rune name, encoded as a little-endian integer with trailing zero bytes elided, present in an input witness tapscript where the output being spent has at least six confirmations.

If a valid commitment is not present, the etching is ignored.

Minting

A runestone may mint a rune by including the rune's ID in the Mint field.

If the mint is open, the mint amount is added to the unallocated runes in the transaction's inputs. These runes may be transferred using edicts, and will otherwise be transferred to the first non-OP_RETURN output, or the output designated by the Pointer field.

Mints may be made in any transaction after an etching, including in the same block.

Transferring

Runes are transferred by edict:

#![allow(unused)]
fn main() {
struct Edict {
  id: RuneId,
  amount: u128,
  output: u32,
}
}

A runestone may contain any number of edicts, which are processed in sequence.

Before edicts are processed, input runes, as well as minted or premined runes, if any, are unallocated.

Each edict decrements the unallocated balance of rune id and increments the balance allocated to transaction outputs of rune id.

If an edict would allocate more runes than are currently unallocated, the amount is reduced to the number of currently unallocated runes. In other words, the edict allocates all remaining unallocated units of rune id.

Because the ID of an etched rune is not known before it is included in a block, ID 0:0 is used to mean the rune being etched in this transaction, if any.

An edict with amount zero allocates all remaining units of rune id.

An edict with output equal to the number of transaction outputs allocates amount runes to each non-OP_RETURN output.

An edict with amount zero and output equal to the number of transaction outputs divides all unallocated units of rune id between each non-OP_RETURN output. If the number of unallocated runes is not divisible by the number of non-OP_RETURN outputs, 1 additional rune is assigned to the first R non-OP_RETURN outputs, where R is the remainder after dividing the balance of unallocated units of rune id by the number of non-OP_RETURN outputs.

If any edict in a runestone has a rune ID with block zero and tx greater than zero, or output greater than the number of transaction outputs, the runestone is a cenotaph.

Note that edicts in cenotaphs are not processed, and all input runes are burned.