Ordinal Theory

Casey Rodarmor's scheme (2022) for numbering individual satoshis. Each of Bitcoin's ~2.1 quadrillion sats has a unique number based on mining order, allowing them to be tracked through transactions.

Numbering scheme

Sats numbered 0, 1, 2, ... based on:

Mining order (block + position).
First-in-first-out (FIFO) through inputs/outputs.

When a tx has inputs [A1, A2] and outputs [B1, B2]:

Sats from A1 flow to B1 first, then overflow to B2.
Within A1, sats are ordered by their original numbers.

Sat rarity classes

Casey defined a fan-following hierarchy:

Common: any sat.
Uncommon: first sat of each block.
Rare: first sat of each difficulty epoch (every 2016 blocks).
Epic: first sat of each halving (every 210k blocks).
Legendary: first sat of each cycle (every 6 halvings, ~24 years).
Mythic: sat #0 (the first sat ever; in Satoshi's coinbase).

Some collectors pay premium for rare sats.

ord client

Reference implementation:

github.com/ordinals/ord (Rust). Latest release as of September 2026: 0.29.0 (5 August 2026). Cadence is bursty rather than monthly - 0.25.0 through 0.27.1 all shipped Feb-Mar 2026, then nothing until 0.28.0 and 0.29.0 in early August 2026 - so re-check the tag list rather than trusting this pin indefinitely.
Indexes the entire chain to compute sat ordinals.
Provides:
- Wallet for sending specific sats (avoid spending rare ones).
- Inscription creation/viewing.
- REST API for querying.

Heavy index: full ord index ~1+ TB on a recent chain, as of September 2026.

Indexed services

ordinals.com — primary explorer.
mempool.space integration for ordinal viewing.
OrdiScan, Ordinalsbot — third-party services.

Use cases

Sat collecting — buying / selling rare sats.
Foundation for inscriptions, BRC-20, Runes, etc.
Provenance tracking — proving a sat originated from a specific block.

Compared to UTXO

Ordinals are an interpretation layer; Bitcoin consensus has no notion of ordinal numbering. The ord client computes ordinals by parsing the chain. Different ord clients must agree on the numbering scheme.

Common confusions

"Ordinals" = sat numbering. Inscriptions = data attached to sats. They're different concepts often conflated.
ord client requires txindex + ord-specific indexing.
"Mythic sat" is just one specific sat (sat #0); not a category of thousands.

bitcoin-metaprotocols-ordinals