What is genesis block?

The first block of a chain, written into the software rather than mined, from which every later block descends.

Bitcoin's was dated 3 January 2009 and carries the headline "Chancellor on brink of second bailout for banks" in its coinbase field, and its fifty-coin reward cannot be spent because of how the software handles that block (source: Bitcoin developer documentation). For proof-of-stake chains the genesis file also fixes the initial validator set and balances, which is where a launch distribution is actually recorded.

Later chains often copy the pattern of embedding a message, and the genesis parameters are the first thing to read when checking a claim about how a launch distributed supply.

The point people overlook is that genesis is where a chain's premine lives. A project can say whatever it likes about a fair launch; the genesis file says what balances actually existed at block zero, and it is a public document.

How it works

Every node needs a starting point it agrees on. Rather than deriving it, the genesis block is hardcoded into the client software, so every node begins from an identical state without having to validate anything before it.

That block fixes several things at once:

• Initial balances. Any allocation to a foundation, a team, investors, or an airdrop set exists here or is created by the first blocks after it.
• The initial validator or difficulty parameters. For a proof of stake chain, who is permitted to produce the first blocks.
• The chain's identity. Because every subsequent block references its parent's hash, the genesis hash is what makes two chains distinguishable even when they run the same software.

Bitcoin's genesis block is unusual in one respect: the fifty-coin reward is not spendable, a consequence of how the original software handles that specific block rather than a deliberate burn.

When a chain splits, the two resulting networks share the same genesis block and diverge later; see fork. When a chain launches fresh, it writes its own.

Example

Illustrative use. A project claims 90% of its token went to the community. You read the genesis allocation and the first vesting contracts and find that a large share sits in addresses controlled by the foundation and early investors, subject to a schedule. Nothing here requires trusting a summary: the balances at block zero are readable on a block explorer, and the vesting contracts state their own terms.

Why it matters when you buy

Launch distribution is the input to every later supply question, including how much is genuinely circulating and how much is scheduled to unlock. Where a project's own claims and its genesis allocation disagree, the chain is the record. Check what is scheduled to arrive at the unlock calendar and how supply is currently split at the concentration pages.

Related terms

block — the unit genesis is the first of, block height — counted from zero at genesis, coinbase transaction — where the embedded message sits, hash — what chains blocks together, fork — chains sharing one genesis, chain id — how networks are distinguished in practice.

Questions

Can the genesis block be changed?

Not without creating a different chain. Every block references its parent, so altering genesis would invalidate everything after it, and nodes running the original software would reject the result.

Are the coins in Bitcoin's genesis block spendable?

No. The fifty-coin reward cannot be spent, a consequence of how the original software handles that block. Coins have been sent to that address since, and those are similarly unrecoverable.

Why does the genesis block matter for a new token?

Because it records the initial allocation. Reading it, alongside the vesting contracts deployed at launch, is how you check a distribution claim against what actually happened.