What it looks like
Random entropy is simply bits: unpredictable zeroes and ones. Sixteen random bytes give 128 bits, enough for a 12-word BIP39 phrase after adding a checksum.
Bitcoin Entropy Lab
Make uncertainty visible.
Entropy is uncertainty that an attacker must guess. A wallet needs enough unpredictable entropy to create private keys no one else can reproduce.
2128
possible starting values
What can go wrong
Dates, quotations, repeated patterns, biased coins, and human-chosen words occupy tiny, guessable corners of the possible range. More characters do not automatically mean more entropy.
How wallets do it
Good wallets use a cryptographically secure random-number generator, ideally with hardware randomness and health checks. Generate keys in a trusted wallet or signing device, never on this page.
Interactive microscope
Build and inspect uncertainty
Learning only. Never use entropy shown by a website to protect real bitcoin.
Ask the operating system
The browser requests cryptographically secure bytes from your device. Regenerating should change roughly half the squares.
Flip a fair coin
Record the result before flipping again. One independent fair flip can contribute one bit. Keyboard: H or T.
Roll a fair six-sided die
Each independent roll carries about 2.58 bits. A real conversion must remove modulo bias; the raw three-bit display below is only a visual trace.
Watch humans make patterns
Type anything. The estimate measures variety inside this sample, not how difficult your idea is to guess from dictionaries or personal information.
Capture a changing environment
Images, movement, and sound contain variation, but their true unpredictability is unknown. Capture a sample, inspect its fingerprint, then mix it with secure device randomness.
Move your pointer inside the field
Microphone audio stays in this browser and is discarded after its fingerprint is made.
Choose an environmental source.
Secure device128 / 128 bits
Cryptographic source- Recorded
- 128 bits
- Balance
- Checking…
- Longest run
- Checking…
- Average guess
- Checking…
Hexadecimal view
Under the hood
Entropy becomes word indexes
BIP39 does not pick twelve words independently. It starts with entropy, appends checksum bits derived from SHA-256, then cuts the result into 11-bit indexes for a 2,048-word list.
128entropy bits
4checksum bits
12BIP39 words
Attacker's view
Small bit counts collapse quickly
Move the control to change the search space. This assumes an unrealistically favorable attacker trying one trillion guesses every second.
Possible values2^32Average guessing timeless than a second