2.11 What Rules Your Node Actually Enforces

When your node receives a new block, it runs a long checklist before accepting it. Here are the big rules:

1) The 21 million supply cap. Your node knows exactly how many coins should exist at every block height. If a miner tries to create even one extra coin, the block is rejected.

2) The halving schedule. The reward for mining a block cuts in half every 210,000 blocks (roughly four years). Your node checks the reward matches the current schedule.

3) Valid signatures. Every Bitcoin being spent must have a valid signature from the correct private key.

4) No double spending. The same coin can't be spent twice.

5) Valid proof-of-work. The block's fingerprint must be small enough to meet the current difficulty.

6) Correct script execution. Any conditions attached to the coins (multisig, timelocks) must be satisfied.

If any rule is broken, your node rejects the block — even if every miner on Earth accepts it. That's the deep meaning of 'don't trust, verify': you're not asking anyone for permission to know what's true.