Opcodes
Low-level operations.
Opcodes is a free Web3 & DApp Development Fundamentals lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Web3 & DApp Development Fundamentals learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
The EVM Instruction Set
At its lowest level, the EVM runs a sequence of opcodes — single-byte instructions that each do one thing.
Understanding opcodes reveals what your Solidity actually does and where gas goes.
What Is an Opcode?
An opcode (operation code) is a one-byte command the EVM executes. Examples include ADD, MUL, PUSH1, SLOAD, and JUMP.
Each opcode has a name, a numeric value, and a fixed gas cost.
0x01 = ADD
0x02 = MUL
0x60 = PUSH1
0x54 = SLOAD
0x56 = JUMPStack Manipulation Opcodes
Opcodes like PUSH, POP, DUP, and SWAP manage the stack.
PUSH adds a value, POP removes one, DUP duplicates an item, and SWAP exchanges two stack positions.
PUSH1 0x0A // [10]
DUP1 // [10, 10]
PUSH1 0x14 // [10, 10, 20]
SWAP1 // [10, 20, 10]Arithmetic Opcodes
Arithmetic opcodes pop operands and push results: ADD, SUB, MUL, DIV, and MOD.
All math is done on 256-bit unsigned integers (with signed variants available).
PUSH1 0x09 // [9]
PUSH1 0x04 // [9, 4]
SUB // [5] (9 - 4)Comparison and Logic
Opcodes like LT, GT, EQ, AND, OR, and ISZERO handle comparisons and bitwise logic.
They push 1 for true and 0 for false, which control flow then uses.
Memory and Storage Opcodes
Data movement opcodes touch the costly locations:
MLOAD/MSTORE— read/write memorySLOAD/SSTORE— read/write storage
SSTORE is one of the most expensive opcodes.
Control Flow Opcodes
JUMP and JUMPI (conditional jump) move execution to a JUMPDEST marker.
This is how the EVM implements loops and if-statements at the bytecode level.
PUSH1 0x10 // jump target
JUMPI // jump if top of stack != 0
// ... at offset 0x10:
JUMPDEST // valid landing spotEnvironment Opcodes
Opcodes like CALLER, CALLVALUE, ADDRESS, and TIMESTAMP expose context.
For example, CALLER pushes the address that initiated the call (this is what msg.sender compiles to).
Gas Cost per Opcode
Every opcode has a defined gas cost. Cheap ones like ADD cost 3 gas; expensive ones like SSTORE cost up to 20000.
The total gas of a transaction is the sum of all opcodes it executes.
ADD -> 3 gas
MLOAD -> 3 gas
SLOAD -> 2100 gas
SSTORE -> up to 20000 gasFrom Solidity to Opcodes
The Solidity compiler turns each high-level statement into many opcodes.
A single uint x = a + b; becomes PUSH, PUSH, ADD, and an MSTORE or SSTORE depending on where x lives.
Putting It Together
Opcodes are the EVM's atomic instructions for stack, arithmetic, logic, memory, storage, control flow, and environment.
Each carries a gas cost, and your Solidity ultimately becomes a stream of them.
Quick Check
Test your opcode knowledge.
Recap: Opcodes
You learned that:
- Opcodes are one-byte EVM instructions
- They cover the stack, arithmetic, logic, memory, storage, control flow, and environment
SSTOREis among the most expensive- Solidity compiles into many opcodes
Next: accounts and state.
Frequently asked questions
Is the “Opcodes” lesson free?
Yes — the full text of “Opcodes” is free to read here on the web, and the Web3 & DApp Development Fundamentals course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Web3 & DApp Development Fundamentals course, upgrade to CoddyKit PRO.
What will I learn in “Opcodes”?
Low-level operations. You practise Web3 & DApp Development Fundamentals with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Web3 & DApp Development Fundamentals?
No prior experience is required. Web3 & DApp Development Fundamentals on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Opcodes” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Web3 & DApp Development Fundamentals lesson?
Yes. Every Web3 & DApp Development Fundamentals lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.