Learn how Bitcoin really works.
Short, visual lessons that start from zero. Every idea comes with an animated diagram, a real example and links into our own explorer so you can see it on the blockchain.
Bitcoin basics
What Bitcoin is, why it exists and the big ideas behind it, explained without jargon.
What is Bitcoin?
Bitcoin is digital money with no bank in charge. Learn how it works, who keeps the record, and why people use it, in plain English with diagrams.
How does Bitcoin work?
How a Bitcoin payment goes from your wallet to the blockchain: signing, checking, waiting in the mempool, mining and confirmation, step by step.
Who created Bitcoin?
Bitcoin was launched in 2009 by Satoshi Nakamoto, a pseudonym that has never been linked to a proven identity. Here is what is actually known.
The Bitcoin whitepaper, explained
A section-by-section, plain-English guide to the 9-page paper that started Bitcoin: transactions, timestamps, proof of work, incentives and privacy.
Satoshis and Bitcoin units
1 bitcoin = 100,000,000 satoshis. Learn the units BTC, mBTC, bits and sats, convert between them exactly, and see why software counts in sats.
Why there will only be 21 million bitcoin
New bitcoin is issued on a fixed schedule that halves every 210,000 blocks. See the maths behind the 21 million cap and who enforces it.
What does decentralized mean in Bitcoin?
Decentralized means no person, company or government runs Bitcoin. See how power is split between nodes, miners, developers and users.
The double-spending problem
Digital money is easy to copy. Learn how Bitcoin stops anyone spending the same coins twice, without a bank, using UTXOs, blocks and proof of work.
Is Bitcoin anonymous?
Bitcoin is pseudonymous, not anonymous. Every payment is public forever, and names stay hidden only until something links them to you. Learn how.
How is Bitcoin different from bank money?
A bank balance is a promise from your bank; self-custodied bitcoin is controlled directly by your keys. Compare freezing, supply, fees and reversals.
Where does new bitcoin come from?
Every new bitcoin is created by miners in the first transaction of each block, on a fixed schedule every node checks. See how much and how often.
Transactions
Inputs, outputs, UTXOs, fees and confirmations: how a Bitcoin payment is actually built.
What is a Bitcoin transaction?
A Bitcoin transaction spends existing coins (inputs) and locks new ones to their next owners (outputs). See how it works with a real example.
UTXOs: how Bitcoin balances really work
Bitcoin has no account balances. Your balance is the total of unspent transaction outputs (UTXOs) your keys can unlock. Learn how UTXOs work.
Transaction inputs
An input points to an earlier output by txid and index, and supplies the signature that unlocks it. Learn what an input contains and why it has no amount.
Transaction outputs
Every output is an amount in sats plus a locking script that says who can spend it next. Learn how outputs, addresses and output numbers fit together.
Change outputs
When you spend a coin worth more than the payment, the rest returns to you as a change output. Learn why change exists and why it can matter for privacy.
How Bitcoin transaction fees work
Bitcoin fees are inputs minus outputs, priced by size in sat/vB, not by amount sent. Learn what sets fees, how to pay less and how to fix a stuck payment.
Fee rate: sats per vbyte
Fee rate is the fee divided by virtual size, in sats per vbyte (sat/vB). It is the number miners sort by. Learn how to calculate and choose one.
Transaction size, weight and vbytes
Since SegWit, transactions are measured in weight units and vbytes, with witness data discounted. Learn how size is counted and why it sets your fee.
Transaction IDs (txid)
A txid is the double SHA-256 hash of a transaction, shown in reverse byte order. Learn how it is made, where to find it and how to look one up.
What is a Bitcoin confirmation?
A confirmation means your transaction is in a block, and each new block adds another. Learn how many you need, how long they take and why they matter.
Replace-by-fee (RBF)
Replace-by-fee lets you resend an unconfirmed Bitcoin transaction with a higher fee so it confirms faster. Learn the rules and how wallets do it.
Child pays for parent (CPFP)
CPFP speeds up a stuck Bitcoin transaction by spending its output in a new high-fee child. Miners take both together. Learn when and how to use it.
The coinbase transaction
The first transaction in every block, created by the miner, pays out the new-coin subsidy plus all fees. Learn its special rules and famous messages.
Locktime and sequence
Locktime stops a transaction confirming before a set block or time; sequence numbers enable RBF and relative timelocks. Learn how both work.
Dust and UTXO consolidation
Dust is an output worth less than it costs to spend. Learn the dust limit, when to consolidate small UTXOs to save fees, and the privacy trade-off.
Transaction batching
Batching pays many recipients in one Bitcoin transaction, sharing fixed costs and saving block space. See how much it saves and who uses it.
Anatomy of a raw transaction
Every Bitcoin transaction is a string of bytes: version, inputs, outputs, witness and locktime. Learn the layout and decode raw transaction hex.
PSBT v0 and v2: format versions, not network forks
Compare the original PSBT format with version 2, including input/output construction, modification flags and compatibility between signing tools.
CompactSize and VARINT: two different encodings
Decode Bitcoin CompactSize lengths with worked byte examples, distinguish Core’s internal VARINT format, and avoid unsafe parser assumptions.
Blocks and the blockchain
How transactions are grouped into blocks and chained together into one history.
What is the blockchain?
The blockchain is Bitcoin's shared history: blocks of transactions, each linked to the one before by its hash. Learn how it works and why it is hard to change.
What is a block?
A Bitcoin block is a batch of transactions plus an 80-byte header that links it to the chain and proves the work done. See what is inside one.
The block header
The block header has six fields in 80 bytes: version, previous hash, merkle root, time, bits and nonce. Learn what each does and why miners hash it.
The genesis block
Block 0, mined on 3 January 2009, started the Bitcoin blockchain. Learn about its newspaper headline, its unspendable 50 BTC and how to view it.
Block height
Block height is a block's position in the chain, counting from 0 at the genesis block. Learn how heights schedule halvings, timelocks and confirmations.
Merkle trees and the merkle root
A merkle tree hashes a block's transactions in pairs until one hash remains: the merkle root. Learn how it works and how merkle proofs save space.
Block size and the weight limit
Bitcoin blocks are limited to 4,000,000 weight units, about 1.5 to 2.5 MB in practice. Learn why the limit exists and how it creates the fee market.
Block timestamps
Miners set each block's timestamp within two rules: later than the median of the last 11 blocks, and at most 2 hours in the future. Learn why.
Stale blocks and chain reorganizations
When two miners find a block at once, nodes briefly disagree, then all switch to the longer chain. Learn how reorganizations work and what they mean for you.
The longest chain (most work) rule
Bitcoin nodes follow the valid chain with the most accumulated proof of work, not simply the most blocks. Learn why and how this creates agreement.
Duplicate transaction IDs and the BIP 30 rule
Explore Bitcoin’s historical duplicate coinbase transactions, the UTXO overwrite problem, and why archival records need block context.
Median time past: Bitcoin’s shared time reference
Calculate median time past with an eleven-block example and understand why Bitcoin timelocks do not promise an exact wall-clock release time.
Mining
How miners compete to add blocks, why it costs energy and how new bitcoin is issued.
What is Bitcoin mining?
Bitcoin mining is a worldwide race to find a rare hash. The winner adds the next block and earns new bitcoin plus fees. Try our mining simulator.
Proof of work
Proof of work means a block's hash is so rare that finding it took huge effort, yet anyone can check it instantly. See how it secures Bitcoin.
The nonce
The nonce is a 4-byte number in the block header that miners change on every attempt. Learn why it runs out so fast and what miners change next.
Target and difficulty
The target is the number a block hash must be below; difficulty says how much harder that is than the first target. Learn how both are calculated.
Difficulty adjustment
Every 2,016 blocks, about two weeks, Bitcoin resets mining difficulty so blocks average 10 minutes again. Learn the formula and the limits.
The block reward
The block reward is what a miner earns for a block: the subsidy (new bitcoin) plus all transaction fees. See today's reward and how it is changing.
The Bitcoin halving
Every 210,000 blocks the new bitcoin per block is cut in half. Halvings happened in 2012, 2016, 2020 and 2024; the next is due around 2028.
Mining pools
A mining pool combines many miners' hash power and shares the rewards, giving each small regular payouts instead of rare jackpots. Learn how pools work.
ASIC miners
ASIC miners are chips built only to compute SHA-256 as fast and efficiently as possible. Learn how they replaced CPUs and GPUs and what specs matter.
Hashrate
Hashrate is how many hashes per second the Bitcoin network performs. It can't be measured directly; learn how it's estimated and why it matters.
The 51% attack
An attacker with most of the hash power could rewrite recent blocks and double spend their own coins, but could not steal coins or change Bitcoin's rules.
Cryptography
Hash functions, signatures and elliptic curves, the tools that make Bitcoin secure.
Hash functions
A hash function turns any data into a short, fixed-size fingerprint, and one changed letter changes it completely. Try it live and see how Bitcoin uses it.
SHA-256
SHA-256 is the hash function Bitcoin uses for blocks, transaction IDs and mining, usually applied twice. Learn how it works and test it live.
HASH160 and RIPEMD-160
HASH160 is SHA-256 followed by RIPEMD-160. It turns a 33-byte public key into the 20-byte hash inside most Bitcoin addresses. See how and why.
Hexadecimal
Hex writes each byte as two characters from 0-9 and a-f. Learn to read hashes, keys and raw transactions, and convert numbers with our tool.
Bytes and endianness
Bitcoin stores most numbers least-significant byte first (little-endian), which is why txids and block hashes look reversed in raw data. Learn why.
Digital signatures
A digital signature proves you hold a private key without revealing it. Learn how Bitcoin signatures authorise every spend and why they can't be reused.
Elliptic curve cryptography
Bitcoin keys live on the secp256k1 curve, y² = x³ + 7. Multiplying a point is easy and undoing it is practically impossible. See how it works.
ECDSA signatures
ECDSA is the signature scheme Bitcoin used from the start. A signature is two numbers, r and s. Learn how it works and why nonce reuse is fatal.
Schnorr signatures
Taproot introduced Schnorr signatures: a fixed 64 bytes, simpler maths, batch verification and multi-party key aggregation. Learn what changed.
Randomness and entropy
A private key is only as safe as the randomness that made it. Learn what entropy means, how weak randomness led to real thefts, and how to stay safe.
Keys and addresses
Private keys, public keys, addresses, seed phrases and HD wallets.
Private keys
A private key is a secret 256-bit number that controls your bitcoin. Learn what it looks like, how it creates addresses and how to keep it safe.
Public keys
A public key is a point on the secp256k1 curve, calculated from your private key. Learn its formats, how it becomes an address and when it is revealed.
Bitcoin addresses
A Bitcoin address is a short code that tells a sender how to lock coins to you. It is not an account and holds no balance by itself. Learn how it works.
Bitcoin address types compared
Compare Bitcoin address types: Legacy (1…), P2SH (3…), native SegWit (bc1q…) and Taproot (bc1p…). See costs, compatibility and which to use.
Base58Check encoding
Base58Check writes data using 58 easy-to-read characters plus a 4-byte checksum that catches typos. Learn how legacy addresses and WIF keys are built.
Bech32 and Bech32m
bc1 addresses use Bech32 (SegWit v0) or Bech32m (Taproot and later). They are lowercase, QR-friendly and catch typos. Learn how they are built.
Seed phrases (BIP 39)
A seed phrase is 12 or 24 words that encode the randomness behind every key in your wallet. Learn how it works, and how to store it safely.
HD wallets (BIP 32)
A hierarchical deterministic (HD) wallet derives an endless tree of keys from one seed, so a single backup restores everything. Learn how it works.
Derivation paths
A derivation path like m/84'/0'/0'/0/0 says exactly where a key sits in an HD wallet. Learn how to read one and fix a restore that shows zero balance.
Extended public keys (xpub)
An xpub can generate every receiving address of a wallet account without being able to spend. Learn its uses and why you should keep it private.
WIF private key format
WIF writes a single Bitcoin private key in Base58Check so it can be copied between wallets. Learn the format, the prefixes 5, K and L, and how to sweep.
Output descriptors: a wallet’s script blueprint
Learn how Bitcoin output descriptors combine keys, derivation paths and script types, and why recovering keys alone may not recover a wallet.
Descriptor checksums: detect errors, not ownership
Understand Bitcoin descriptor checksums, what they protect during backup and import, and why a valid checksum cannot authenticate a wallet policy.
Bitcoin Script
The small language that decides who can spend each output, from P2PKH to Taproot.
Bitcoin Script
Every Bitcoin output is locked by a tiny program written in Script. Learn how locking and unlocking scripts work together and why Script is limited.
The stack
Bitcoin Script runs on a stack: items go on top and operations take them off. Watch a simple script execute step by step with an animated diagram.
Script opcodes
Opcodes are Bitcoin Script's instructions: duplicate, hash, compare, check signatures and times. A clear reference to the opcodes you will see most.
Pay to public key (P2PK)
The earliest Bitcoin outputs locked coins directly to a public key. Learn how P2PK works, where to find it, and why it was replaced by P2PKH.
Pay to public key hash (P2PKH)
P2PKH locks bitcoin to the hash of a public key; to spend, you reveal the key and a signature. Step through the script with an animated diagram.
Pay to script hash (P2SH)
P2SH locks bitcoin to the hash of a script that is revealed only when spending, giving complex conditions a short address. Learn how it works.
Multisig
Multisig requires several keys to sign, such as 2 of 3, removing single points of failure for theft and loss. Learn how to set it up safely.
Timelocks: CLTV and CSV
Timelocks stop bitcoin being spent until a set time. CLTV uses an absolute block or date; CSV counts from when the coins were received. See examples.
Segregated Witness (SegWit)
SegWit (2017) moved signatures into a separate witness section, fixing malleability, discounting signature data and making Lightning practical.
Taproot
Taproot (2021) lets complex Bitcoin spending conditions look like ordinary payments, using Schnorr signatures and hidden script branches. Learn how.
Witness data
The witness is the part of a SegWit transaction holding signatures and unlocking data. It sits outside the txid and is discounted. Learn how it works.
OP_RETURN data outputs
An OP_RETURN output carries data and can never be spent, so it never bloats the UTXO set. Learn how it works, what it is used for and its limits.
Nodes and the network
Nodes, peers, the mempool, consensus rules and how Bitcoin upgrades.
What is the Bitcoin mempool?
The mempool is each node's waiting room for valid transactions not yet in a block. Learn how it works, why it fills up and how to read it live.
What is a Bitcoin node?
A Bitcoin node is a computer that checks every block and transaction against the rules. Learn what nodes do, why to run one and what it takes.
Full nodes vs pruned nodes
A pruned node verifies everything an archival node does, then deletes old blocks to save disk space. Compare both and choose the right one.
The peer-to-peer network
Bitcoin nodes connect to a handful of peers and pass on new transactions and blocks, so news spreads worldwide in seconds. Learn how gossip works.
Initial block download (IBD)
A new Bitcoin node must download and verify every block since 2009 before it is caught up. Learn what initial block download involves and how to speed it up.
Consensus rules
Consensus rules decide what makes a Bitcoin block or transaction valid. Every node enforces them, and a block that breaks one is rejected. See examples.
Relay policy and standardness
Nodes apply extra rules about which transactions they relay and keep in their mempool. Learn how policy differs from consensus and why it matters.
Soft forks and hard forks
A soft fork tightens Bitcoin's rules so old nodes keep working; a hard fork loosens them so old nodes reject the new chain. Learn the difference.
Bitcoin Improvement Proposals (BIPs)
BIPs are design documents proposing changes or standards for Bitcoin. Some change consensus; many just help wallets work together. See the key ones.
SPV and light clients
Light (SPV) clients download only block headers and check merkle proofs, trusting the most-work chain instead of verifying every rule. Learn the trade-offs.
Transaction indexes versus address-history indexes
See why a synced Bitcoin node may find blocks but need a separate index for transaction IDs, address history or complete explorer reports.
Keep Bitcoin Core RPC private
Learn why Bitcoin Core RPC is a privileged control interface, how it differs from public explorer APIs, and what authentication does and does not protect.
Compact block filters: find relevant blocks privately
Learn how BIP 157 and BIP 158 help light clients find potentially relevant blocks, why matches can be false positives, and what validation still remains.
Block files, chainstate and undo data
Understand the different jobs of Bitcoin Core’s block files, UTXO database, undo records and indexes before planning storage or recovery.
AssumeUTXO: snapshots and background validation
Learn how Bitcoin Core boots from a recognized UTXO snapshot, what background validation still does, and why historical indexes can lag behind.
Wallets and security
Self-custody, backups, hardware wallets and privacy habits.
What is a Bitcoin wallet?
A Bitcoin wallet doesn't hold coins; it holds keys, finds the coins they control, and builds and signs transactions. Learn how to choose one.
Self-custody vs custodial
With self-custody you hold the keys and the responsibility; with a custodian such as an exchange, someone else does. Compare the risks and choose.
Hot and cold wallets
Hot wallets keep keys on an internet-connected device; cold storage keeps them offline and signs there. Learn how cold signing works and when to use it.
Hardware wallets
A hardware wallet stores your Bitcoin keys and signs transactions inside a dedicated device, so malware on your computer can't steal them. Learn how to use one.
How to back up a Bitcoin wallet
Write your seed phrase on paper or metal, store it offline, never digitally, and test that recovery works. A step-by-step guide to Bitcoin backups.
The seed passphrase ("25th word")
An optional passphrase combines with your seed to create a different wallet, protecting you if the seed is stolen. Learn the benefits and the risks.
Address reuse and privacy
Every payment to a reused Bitcoin address is publicly linked. Learn why a fresh address each time protects your privacy and how wallets do it for you.
Coin control
Coin control lets you choose exactly which UTXOs a Bitcoin transaction spends, for lower fees, better privacy and avoiding dust. Learn how to use it.
Watch-only wallets
A watch-only wallet tracks balances and builds transactions from public keys only, so it can never spend by itself. Learn its uses and privacy cautions.
PSBT: prepare, inspect and sign a Bitcoin payment
Follow a partially signed Bitcoin transaction through preparation, signing and finalization, with a worked fee example and clear privacy boundaries.
Why a pruned node cannot always rescan an old wallet
Understand the difference between validating old blocks and retaining them, and why wallet recovery can need historical data that a pruned node deleted.
Lightning Network
Payment channels, routing and invoices: Bitcoin payments in seconds.
The Lightning Network
Lightning is a network of payment channels on top of Bitcoin. Payments settle in seconds for tiny fees without a new on-chain transaction each time.
Payment channels
A Lightning payment channel is a 2-of-2 multisig output plus signed, unbroadcast transactions that record the latest balance. Learn how channels work.
Lightning routing
Lightning payments hop through a path of channels chosen by the sender, wrapped in onion layers so each hop sees only its neighbours. Learn how routing works.
HTLCs: hash time-locked contracts
An HTLC pays someone who reveals a secret before a deadline and otherwise refunds the sender. It makes multi-hop Lightning payments trustless. See how.
Lightning invoices
A Lightning invoice is a payment request with the amount, payment hash, expiry and routing hints. Learn how BOLT 11 invoices and BOLT 12 offers work.
Channel liquidity
On Lightning you can only send what's on your side of a channel and receive what's on the other side. Learn how to manage inbound and outbound liquidity.
Closing channels and watchtowers
Lightning channels close cooperatively or by force. Watchtowers watch the blockchain and punish cheating while you are offline. Learn how closing works.
Using a block explorer
How to read blocks, transactions and traces, and what an explorer cannot tell you.
How to read a block explorer
A Bitcoin block explorer is a search engine for the blockchain. Learn what every field on a block, transaction and address page means, step by step.
How to look up a Bitcoin transaction
Find any Bitcoin transaction by its txid, read its status, fee and confirmations, and learn what to do when a transaction can't be found or is stuck.
What a Bitcoin trace can and can't prove
Following bitcoin from transaction to transaction is factual; claims about owners or which input paid which output are assumptions. Learn to read a trace.
Chain analysis heuristics
Chain analysis groups Bitcoin addresses using rules of thumb such as common-input ownership and change detection. Learn how they work and when they fail.