⬡Playground Beginners Technical Glossary About

Free · No signup · Open source ethos

The code that locks
every Bitcoin — run it yourself.

Bitcoin Script is a stack-based language with no loops and no variables — just a stack. BitcoinMachine teaches you to read, write, and reason about it by letting you run a real interpreter, live.

Start the course →⬢ Open Playground

8: Guided modules
40+: Opcodes
50: Runnable examples
Free: Forever, no signup

Live · OP_2 OP_3 OP_ADD OP_5 OP_EQUAL

Script

▶OP_2

OP_3

OP_ADD

OP_5

OP_EQUAL

Stack0 items

↑ top of stack

nothing here yet

press Step or Run to push an item

bottom

OP_2—Pushes the number 2 onto the stack.

0 stepsReady

Press Space to step — this is the same engine that runs the course.

See it in 90 seconds

We cracked open the black box.

Watch how a transaction is validated — push two, push three, add, and ask: does it equal five? Then step through it yourself.

Three ways in. One machine underneath.

Guided course

Eight modules, one machine

Start at last-in-first-out and build, opcode by opcode, toward the scripts that secure real coins. No math degree required.

Start Module 1 →

Live playground

A real Script interpreter

40+ opcodes, a drag-and-drop builder, and 50 runnable examples. Write a script, step through it, watch the stack come alive.

Open Playground →

Deep glossary

Meets you where you are

Plain-English explainers for beginners, and deep interactive breakdowns — elliptic curves, Schnorr, Merkle roots, Bech32.

Browse the glossary →

Eight modules. One machine.

Start with last-in-first-out and build toward the scripts that secure real coins.

The Stack

A last-in, first-out machine with no variables, no loops, no heap. Master push, pop, and the five fundamental stack opcodes.

Arithmetic

Script integers use CScriptNum, where zero is the empty byte array. Addition, subtraction, negation, and range checks.

Comparison

Assert conditions without branching. Understand the difference between byte equality and numeric equality.

Branching

OP_IF and OP_NOTIF are Script’s only conditional. The exact mechanism Lightning HTLCs depend on.

Crypto Primitives

Five hash functions baked into Script: SHA-256, HASH256, RIPEMD-160, HASH160 — the building blocks of every address.

Signatures

OP_CHECKSIG is what makes ownership real: only the holder of a private key can produce a valid signature.

P2PKH

The script behind every address starting with “1”. Trace all six opcodes and why the key is hashed on-chain.

Multisig

OP_CHECKMULTISIG enables shared custody: M of N keyholders must sign — the 2-of-3 that guards cold storage.

CA

Built by Chatzis Athanasios — with Bitcoin since 2012, on one belief: this should be open to everyone.

From your first push, to your first signature.

The stack is the computer. Start where it begins.

Start Module 1 →⬢ Open Playground