Yellow paper

A yellow paper sits one level deeper than a whitepaper: where a whitepaper explains a project's vision and goals in accessible language for a general audience, a yellow paper spells out the exact technical rules of a protocol using formal mathematical notation, algorithms, and pseudocode, detailed enough that a developer could build a fully compatible client from it alone.

The best known example is the Ethereum Yellow Paper, written by co-founder Gavin Wood in 2014 and titled "Ethereum: A Secure Decentralised Generalised Transaction Ledger." It formally defines the Ethereum Virtual Machine, gas costs, the state transition function, and the exact structure of blocks and transactions. Rather than a one-time release, it remains an open source project maintained by contributors on GitHub and periodically updated as the protocol evolves through network upgrades.

Other blockchain projects, most notably Polkadot, have published their own yellow papers to give developers an authoritative technical reference beyond marketing-oriented introductions. Because these documents rely on dense mathematical language, they are written less for investors and more for:

• Core developers implementing or auditing client software
• Security researchers verifying protocol behavior
• Academics studying blockchain design

In practice, a project's whitepaper and yellow paper complement each other: one sells the idea, the other proves precisely how it works under the hood.