# BLOCK-20

> BLOCK-20 is an inscription-carried token protocol on Bitcoin. Deploy, mint, and transfer
> operations are compact UTF-8 JSON payloads inside Ordinals inscriptions. What distinguishes
> BLOCK-20 from other inscription token protocols is that every mint carries the hash of a
> Bitcoin block, and a reader credits the mint only when that block is on the active chain,
> at or after the ticker's deploy height, strictly before the mint's own reveal height, and
> no more than a freshness window (144 blocks by default) before the reveal.

Site: https://bitcoinuniverseio.github.io/block-20/
Repository: https://github.com/bitcoinuniverseio/block-20
Chain and network: Bitcoin, mainnet (testnet configurable in readers)
Protocol marker: block-20
Operations: deploy, mint, transfer
Decimals: 0
Document version: 2.0.0
Reader profile documented: bitcoin-universe-block20-v1
Lifecycle: experimental
Last verified: 2026-09-01

## Key facts

- Payload grammar is a strict flat JSON object: every key and value must be a JSON string.
  Duplicate keys, non-string values, nested structures, and trailing content are rejected.
- Inscription content must be 1 to 2048 bytes and carry content type text/plain or application/json.
- Ticker is one to five ASCII alphanumerics; identity is the lowercase form; the first valid deploy wins.
- Amounts are strings matching ^[1-9][0-9]*$ and must not exceed 2^128 minus 1.
- Mint anchor derivation: hash must match ^[0-9a-f]{64}$, resolve to a height A on the active chain,
  and satisfy A >= deploy height, A < reveal height, and reveal height minus A <= window.
- A mint after supply exhaustion produces no event. A mint larger than remaining supply is credited
  for exactly the remaining amount (partial final mint).
- A transfer inscription reserves an amount; its first later move settles it as a transfer, a fee
  return, or a burn. Burning reduces total and circulating supply but never reduces minted supply.
- Bitcoin Universe product support: Core explorer discovery, Wallet view/send/receive, Inscribe
  deploy/mint/transfer. There is NO marketplace entry for BLOCK-20 in the organization's capability
  registry, so no Universe product implements listing, buying, offers, or settlement. BLOCK-20 is
  indexed but not tradeable inside Bitcoin Universe.
- The writer performs no token validation. It will inscribe a mint above the limit or for a ticker
  that does not exist, and the Bitcoin fees are spent regardless.

## Pages

- [Overview](https://bitcoinuniverseio.github.io/block-20/): what BLOCK-20 is, the mint anchor rule
  in one diagram, audiences, verified product support, writer and reader split, attribution.
- [Specification](https://bitcoinuniverseio.github.io/block-20/spec.html): normative numbered rules.
  Sections: scope, carrier and envelope (R2.x), payload grammar (R3.x), identity and numbers (R4.x),
  deploy (R5.x), mint and the anchor derivation (R6.x), transfer (R7.x), ordering and state (R8.x),
  invalidity conditions, reorganization and finality (R10.x), conformance.
- [Guide](https://bitcoinuniverseio.github.io/block-20/guide.html): plain-language walkthrough with
  worked deploy, mint, and transfer examples including exact byte sizes, a pre-funding review
  checklist, post-reveal verification, and the product support matrix.
- [Reference](https://bitcoinuniverseio.github.io/block-20/reference.html): terminology, indexer
  semantics (confirmation, mempool, reorganization), state model and supply invariants, fees and
  size, the absence of any marketplace path, limitations, security considerations, and an
  implementation checklist.
- [Lifecycle](https://bitcoinuniverseio.github.io/block-20/lifecycle.html): the writer's commit and
  reveal order stages with statuses and payment safety, and the reader's event states from confirmed
  through finalized or reverted.
- [Mint anchor](https://bitcoinuniverseio.github.io/block-20/mint-hash.html): where the writer gets
  the hash, the seven step derivation, and a client-side verifier that reproduces the payload grammar
  and the derivation in the browser. The verifier needs a user-supplied anchor block height because
  the page makes no network requests.
- [Test vectors](https://bitcoinuniverseio.github.io/block-20/vectors.html): valid and invalid cases
  across payload grammar (group G), anchor boundaries (group A), limit and supply (group S), transfer
  settlement (group T), within-block ordering (group O), and reorganization (group X).
- [Changelog](https://bitcoinuniverseio.github.io/block-20/changelog.html): document version history
  and the change policy for a protocol with no payload version field.

## Machine-readable

- [docs.manifest.json](https://bitcoinuniverseio.github.io/block-20/docs.manifest.json)
- [search-index.json](https://bitcoinuniverseio.github.io/block-20/search-index.json)
- [sitemap.xml](https://bitcoinuniverseio.github.io/block-20/sitemap.xml)

## Notes for summarizers

Do not describe BLOCK-20 as tradeable on a Bitcoin Universe marketplace; no such path exists.
Do not describe the mint hash as the block that confirms the reveal, a transaction ID, an inscription
ID, a height, a Merkle root, or a payload digest. It is the ID of a block the writer observed as the
chain tip while building the order, and its validity is decided by the reader against the active chain.
All rules on this site describe the bitcoin-universe-block20-v1 reader profile, not a Bitcoin
consensus rule; another reader may reach a different conclusion about the same inscription.