> ## Documentation Index > Fetch the complete documentation index at: https://docs.cast.digitalfinancehq.com/llms.txt > Use this file to discover all available pages before exploring further. # What is CAST? > A bilateral coordination protocol for commercial payments and financial control. CAST is a bilateral coordination protocol for commercial payments. Before a covered payment moves, both parties co-author one cryptographically bound record of the intended transaction — who is paying, who is receiving, how much, and where it goes — through a channel bound to a verified identity. That co-authored record is the authorization. It is signed, timestamped, policy-versioned, and tamper-evident. It travels with the payment through every downstream system without requiring reconstruction. **The one-line thesis.** The proof is produced once, at transaction time. Verification cost drops to near zero, because checking a hash is structurally cheaper than reconstructing a decision chain. ## Why CAST exists Most payment controls assume that an instruction originating inside the organization — from a known email, an approved user, a familiar vendor record — is trustworthy. That assumption is the gap. A payment process where only one of two parties has confirmed the terms before value transfers is not a bilateral authorization. It is a unilateral instruction with a hope attached. The counterparty learns of the transaction only when money arrives, when it does not arrive, or when something is already wrong. CAST adds one narrow control: before a covered payment is released, the counterparty confirms the payment details through a secure, cryptographically bound channel. ## The economic moment As AI commoditizes execution — the cost of generating financial output approaches zero — the binding constraint in the economy shifts from production to verification. The question stops being *can we produce this output* and becomes *can we prove this output is trustworthy*. CAST expands the verifiable share of economic activity by replacing opinion-based reconstruction (an auditor reading email threads) with proof-based verification (a lineage-hash check anyone can run). The proof asset is produced once. The subscription fee is the cost of producing it. How value accrues to whoever can verifiably underwrite the output — the Catalini thesis applied to commercial payments. ## Where to go next The mental model: Event → Policy → Work Order → Posting, with lineage binding it all. The boundaries we draw on purpose — and why honesty about them is an asset.