Inscriptions

Casey Rodarmor's scheme (Jan 2023) for embedding arbitrary data on Bitcoin via Taproot script-path commitments. Combined with ordinals, each inscription is "owned by" a specific sat.

Mechanism

1. Construct a Taproot script tree containing an "envelope" leaf:
   OP_FALSE
   OP_IF
       OP_PUSH "ord"
       OP_PUSH 1                ; field 1 = content type
       OP_PUSH "image/png"
       OP_PUSH 0                ; field 0 = body
       OP_PUSH <data chunks>
       ...
   OP_ENDIF
2. Commit to the script tree in a Taproot output.
3. Reveal the inscription via spending that output, using script-path:
   - Witness includes the envelope + control block.
   - Data appears in the witness on chain.

The data is "inscribed on" the first sat of the spent input.

Two-tx pattern

Most inscriptions use a 2-tx pattern:

Commit tx: pay-to-Taproot output committing to envelope.
Reveal tx: spend commit output, revealing inscription in witness.

This pattern allows re-use of prior key/script tree.

Inscription envelope fields

field 0: body (the actual data)
field 1: content_type (MIME type)
field 2: pointer (sat offset within UTXO)
field 3: parent (parent inscription ID for relationships)
field 5: metadata (CBOR-encoded)
field 7: metaprotocol (e.g., "brc-20")
field 9: content_encoding (e.g., "br" for brotli)

Recursive inscriptions

Field 6: delegate lets one inscription reference content of another. Forms a graph; saves bytes by re-using inscribed data.

Inscription "scripts" that load JS/SVG/HTML can use /r/inscription/<id> URLs to fetch other inscriptions on-chain.

Privacy / cost impact

Inscriptions consume witness space, which is discounted 4x in fee accounting. But they still cost real money:

A 100 KB inscription costs ~25,000 vB ≈ a normal small block-size worth of fees.
Big inscriptions (1+ MB images) can cost equivalent of a typical full block.

Inscription waves

Jan 2023: launch; high fees triggered.
May 2023: BRC-20 wave caused massive fee spike.
Q1 2024: ongoing constant inscription activity.
April 2024: Runes launch (different mechanism, similar effect).

Use cases

Bitcoin NFTs — JPEG, PNG, SVG, HTML.
BRC-20 tokens (covered separately).
Recursive apps — JS/HTML on chain.
Provenance — digital art ownership.

Relay policy: datacarrier / OP_RETURN

In Bitcoin Core the -datacarrier* options govern OP_RETURN outputs only, so they never applied to inscriptions, which ride in the witness. Knots differs: -datacarrierfullcount defaults to 1 there ("Apply datacarriersize limit to all known datacarrier methods") and its DatacarrierBytes() walks the input witness, so the Knots -datacarriersize=83 default does bear on envelopes (v29.4.1.knots20260508, Sept 2026). Core's defaults changed materially in 30.0 (October 2025) and still stand in 31.1 (July 2026):

                       <= 29.x      30.0+
-datacarriersize       83 bytes     100,000 bytes (aggregate)
OP_RETURN outputs/tx   1            many (relay + mining)
-minrelaytxfee         1 sat/vB     0.1 sat/vB
-incrementalrelayfee   1 sat/vB     0.1 sat/vB
-blockmintxfee         1 sat/vB     0.001 sat/vB

100,000 bytes "effectively uncaps the limit, as the maximum transaction size limit will be hit first" (30.0 release notes): an OP_RETURN scriptPubKey is non-witness, 4 WU per byte, so 100 KB of it already blows past the 400,000 WU standard-tx weight limit.

Consequences for metaprotocols:

OP_RETURN is now a relay-viable data channel of effectively arbitrary size, and no longer capped at one output per tx. Matters most for protocols that encode state there (Runes).
It does not make OP_RETURN cheaper than a witness envelope: witness bytes cost 1 WU, OP_RETURN bytes cost 4 WU, so bulk inscription payloads stay ~4x cheaper in the witness.
Both options still exist and are still settable; -datacarriersize=83 restores the old cap. The removal proposal discussed during 30.0 development was dropped — neither option carries a deprecation marker as of 31.1 (July 2026).

Status / criticism

Some Bitcoin developers see inscriptions as chain spam — using chain space for non-monetary data. Bitcoin Knots filters them by default: at v29.4.1.knots20260508 (Sept 2026) -rejectparasites=1 ("refuse to relay or mine parasitic overlay protocols") and -rejecttokens=1 are the shipped defaults, alongside -datacarriersize=83 and -minrelaytxfee of 1 sat/vB.

Counterview: inscriptions pay full market fees, are legitimate tx, and can't be filtered without arbitrary mempool policy that deviates from consensus. Core moved its own defaults the other way (see above); the uncapping merged as PR #32406 on 9 June 2025, four months before 30.0 shipped on 13 October 2025. The dispute ran alongside a node-share surge over the same period: Knots went from ~400 reachable nodes in Jan 2025 to a peak of 7,112 on 14 Sep 2025, and sits at 4,399 — 17.0% of 25,864 reachable public nodes — as of 15 September 2026 (coin.dance). Reachable-node counts are not sybil-resistant, so read that surge as a signal, not a headcount.

On Core's chain this stays policy, not consensus: a filtered tx remains valid and confirms as soon as any miner includes it. That is no longer true of current Knots builds. BIP-110 ("Reduced Data Temporary Softfork") invalidates, at the consensus layer, Tapscripts that execute OP_IF/OP_NOTIF, pushdata payloads and script-argument witness items over 256 bytes, and Taproot annexes — which covers the inscription envelope itself. Its mandatory-signaling window opened on 8 August 2026, the chain split, the minority chain stalled, and the BIP was marked Closed in the BIPs repo days later (bips#2245, "following a chain split with stalled mining"). It never reached its 55% threshold by signaling; instead it took effect as a flag day at block 961,640 (30 August 2026), the first block of a separate BLAKE2b proof-of-work chain, with the data limits running to 1 September 2027. That change shipped in the v29.4.1.knots20260508 line (rc1 tagged 21 August 2026; final release 2 September 2026). UTXOs created before the flag-day height are grandfathered, so inscriptions made earlier stay spendable there. So as of September 2026: policy on Core's chain, consensus on the Knots BLAKE2b chain — and those are two different chains. See ../../core/knots/SKILL.md.

Tools

ord client — primary creation/viewing.
OrdinalsBot, Gamma.io — services for minting + marketplace.
Magic Eden — history: its Ordinals/Runes marketplace closed 9 March 2026 and the Bitcoin API followed on 27 March 2026. api-mainnet.magiceden.dev/v2/ord/btc/* returns 503 no healthy upstream as of September 2026 — do not code against it.
OrdiScan, mempool.space — explorers with inscription view.

Common bugs

Reveal tx must spend the commit's output; if you spend a different output, no inscription is created.
Sat tracking: ord computes which sat owns the inscription (first sat of first input). Mistakes here lose the inscription's identity.
Content too large: many providers reject > a few MB.

bitcoin-metaprotocols-inscriptions