Runes

Casey Rodarmor's fungible token protocol for Bitcoin. Activated at the 2024 halving (April 2024). Architecturally cleaner than BRC-20 — uses Bitcoin's UTXO model directly.

Mechanics

A Rune's state is encoded in OP_RETURN outputs called runestones:

OP_RETURN OP_13 <protocol_message>

OP_RETURN OP_13 (0x6a 0x5d) is the Rune protocol marker.

The protocol message is varint-encoded, specifying:

• Edicts — transfer instructions (rune ID, amount, output index).
• Etching — issuance of new rune.
• Pointer — default output for unspecified rune balances.

Relay policy: the runestone is an OP_RETURN

Because the whole protocol message rides in an OP_RETURN, the node's -datacarrier* policy decides whether an etch, mint or transfer propagates at all. Core and Knots diverge sharply here.

Bitcoin Core 30.0 (October 2025) raised the -datacarriersize default to 100,000 bytes, applied to the aggregate scriptPubKey size across all nulldata outputs, and began relaying and mining multiple OP_RETURN outputs per tx. Both still hold in 31.1 (July 2026), where MAX_OP_RETURN_RELAY is MAX_STANDARD_TX_WEIGHT / WITNESS_SCALE_FACTOR = 100,000. Size was never the binding constraint for Runes — a typical mint or single-edict transfer is tens of bytes — but a many-edict transfer or an etching with a long name and full terms can approach the old 83-byte cap.

Bitcoin Knots rejects runestones outright, by name. At v29.4.1.knots20260508 (Sept 2026) -rejecttokens defaults to 1, and IsStandardTx flags any nulldata output whose second byte is OP_13 with the reject reason tokens-runes — i.e. exactly the 0x6a 0x5d marker above. The 83-byte MAX_OP_RETURN_RELAY, the one-nulldata-output rule (multi-op-return) and -rejectparasites=1 are also Knots defaults, but -rejecttokens is the one that matters: on a default Knots node no runestone relays, whatever its size. Operators who want Runes traffic must set -rejecttokens=0.

Consequence: a runestone that your Core node accepts can still stall if the peers or the miner in front of it run Knots. Check the reject reason before assuming an encoding bug.

Rune ID

Identified by <block>:<tx_index> of the etching tx. E.g., 840000:1 = the 2nd Rune etched at block 840000.

Etching (issuance)

runestone {
    etching {
        rune: "BITCOIN.MAGAZINE",
        symbol: "B",
        divisibility: 8,
        spacers: 1024,            // visual spacing in display
        premine: 1000,           // amount to etcher
        terms {
            cap: 21_000_000,
            amount: 100,         // per-mint amount
            height: [840000, 1000000],   // mintable in this block range
            offset: [0, 525960],          // or relative-time
        }
    }
}

Mint

runestone {
    mint: 840000:1,    // mint this rune
}

Mint is allowed if:

• The rune has open mint (cap not reached, time/block in range).
• Sender provides enough fee (no specific token gating).

Transfer

runestone {
    edicts: [
        { id: 840000:1, amount: 100, output: 1 },
    ],
}

Output 1 receives 100 of rune 840000:1. Rest of rune balance defaults to "first non-runestone output" or pointer.

Compared to BRC-20

Indexers

• mempool.space — decodes runestones inline in the transaction view (shared/ord/rune.utils.ts); there is no standalone Runes browser or /runes route, and the REST API exposes no Runes endpoints (checked September 2026).
• UniSat — wallet + Runes index; UniHexa, its self-custody Bitcoin-asset exchange, is still pre-launch as of September 2026 — unisat.io marks it "Coming Soon" and links only to a beta host.
• OKX — Runes exchange.
• Xverse — Runes wallet + mint/portfolio tooling.

Reference impl: ord client (also handles Runes since 0.18.0, 11 April 2024). Latest release as of September 2026: 0.29.0 (5 August 2026).

Magic Eden exited Bitcoin (history). Magic Eden ran the dominant Ordinals/Runes venue — reported at roughly 80% of Bitcoin Ordinals/Runes trading volume at its 2023-2024 peak — then wound it down in 2026 to refocus on Solana. Per its own service-change notice: Bitcoin marketplace support ended 9 March 2026, the Bitcoin/Runes APIs were discontinued 27 March 2026, and the Magic Eden Wallet left the app stores 1 April 2026 and shut down fully 1 May 2026 (keys not exported before then are unrecoverable). api-mainnet.magiceden.dev/v2/ord/btc/* returns 503 no healthy upstream as of September 2026 — do not code against it.

Use cases

• Memecoins (DOG•TO•THE•MOON, RSIC•GENESIS•RUNE, etc.).
• Loyalty tokens.
• Limited issuance assets.

Activation impact

April 2024 halving: Runes activated → massive fee spike (Block 840,000 had record mempool congestion). Subsequent weeks of high fees as etching frenzy continued.

Trade-offs vs BRC-20

Runes are:

• More efficient (smaller footprint).
• Native (validation rules are part of protocol, not indexer).
• Newer (less ecosystem maturity at launch but fast-growing).

Common bugs

• Forgetting pointer field → defaults can send tokens to wrong output.
• Encoding errors in varint payload → tx is silently a no-op for Runes.
• Mint outside cap/time → indexer marks invalid.

See also

• brc-20/SKILL.md
• atomicals/SKILL.md
• ordinals/SKILL.md
• inscriptions/SKILL.md