What is the ledger?

Our append-only, tamper-evident record of forecasts. It records what was forecast, by whom, when it was made, when we captured it, how it resolved and how it was scored, and it makes any later edit, deletion, reordering or truncation detectable. Proof of Call is built on it. Live recording was switched on in October 2026. See Is the ledger recording yet?

Details

• Append-only. Nothing is edited or deleted. Mistakes get a visible correction record that points to the original.
• Hash-chained. Each record includes the hash of the one before it. See the glossary.
• Sealed daily. Each UTC day gets a "head": a fingerprint of that day's records, chained to the previous day's. Empty days get heads too, so gaps are visible.
• Anchored publicly. Daily heads go to a public GitHub repository, nothingbutalpha/ledger-heads. See ledger-heads.
• Rules are data. Scoring rules are recorded in the ledger and versioned. A forecast is scored only under the rule version it declared.
• Live means live. Whether a call was captured live or backfilled is part of the record and is checked against its timestamps.
• Recomputable. The format is deterministic, so anyone with the data can recompute every hash with short, standard-library Python.

Format name: nba-ledger/1. Hashes are SHA-256.