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Run Bytecode examples in the interactive playground
Conceptual Guide - For API reference and method documentation, see Bytecode API.
EVM bytecode is the low-level machine code that smart contracts compile to and execute on the Ethereum Virtual Machine. This guide teaches bytecode fundamentals using Tevm.

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Structure

Bytecode is a sequence of bytes where each byte (or sequence of bytes) represents either:
  • An opcode - Instruction telling the EVM what to do (ADD, PUSH1, JUMP, etc.)
  • Data - Constant values embedded after PUSH opcodes

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Parsing Bytecode

The main challenge: PUSH1-PUSH32 opcodes (0x60-0x7f) are followed by 1-32 bytes of data that are NOT opcodes. 
import { Bytecode } from 'tevm';

// Bytecode: PUSH1 0x5b (0x5b is data, not JUMPDEST opcode)
const code = Bytecode("0x605b");

const instructions = code.parseInstructions();
console.log(instructions);
// [{ opcode: 0x60, position: 0, pushData: Uint8Array([0x5b]) }]

// Tevm correctly identifies 0x5b as data, not JUMPDEST

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Analyzing Structure

Use analyze() for complete bytecode analysis: 
import { Bytecode } from 'tevm';

const code = Bytecode("0x6001600201");

const analysis = code.analyze();
console.log(analysis.valid);              // true
console.log(analysis.jumpDestinations);   // Set<number> of valid JUMPDEST positions
console.log(analysis.instructions.length); // 3 instructions

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What analyze() Returns

type Analysis = {
  valid: boolean;                          // Bytecode structure is valid
  jumpDestinations: ReadonlySet<number>;   // Valid jump targets (JUMPDEST positions)
  instructions: readonly Instruction[];    // Parsed instructions with push data
}

type Instruction = {
  opcode: number;        // Opcode byte (0x00-0xff)
  position: number;      // Byte offset in bytecode
  pushData?: Uint8Array; // Data following PUSH opcodes (undefined for non-PUSH)
}

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Jump Destinations

JUMPDEST (0x5b) markers indicate valid jump targets. The EVM validates that JUMP/JUMPI only target JUMPDEST opcodes: 
import { Bytecode } from 'tevm';

const code = Bytecode("0x5b6001565b60025600"); // Two JUMPDESTs

// Find all valid jump destinations
const jumpDests = code.analyzeJumpDestinations();
console.log(jumpDests); // Set(2) { 0, 5 }

// Check if specific position is valid jump target
console.log(code.isValidJumpDest(0));  // true  (JUMPDEST at position 0)
console.log(code.isValidJumpDest(5));  // true  (JUMPDEST at position 5)
console.log(code.isValidJumpDest(2));  // false (PUSH1 data, not JUMPDEST)

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Disassembly

Use formatInstructions() to disassemble bytecode to human-readable strings: 
import { Bytecode } from 'tevm';

const code = Bytecode("0x6001600201");

const disassembly = code.formatInstructions();
console.log(disassembly);
// [
//   "PUSH1 0x01",
//   "PUSH1 0x02",
//   "ADD"
// ]

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Complete Example: ADD Operation

Here’s bytecode that adds 5 + 3 and returns the result: 
import { Bytecode } from 'tevm';

// Deployment + runtime bytecode
const code = Bytecode("0x6005600301600052602060006000f3");

// Disassemble to understand structure
const instructions = code.formatInstructions();
console.log(instructions);
// [
//   "PUSH1 0x05",  // Push 5 onto stack
//   "PUSH1 0x03",  // Push 3 onto stack
//   "ADD",         // Add top two values (5 + 3 = 8)
//   "PUSH1 0x00",  // Push memory offset 0
//   "MSTORE",      // Store 8 at memory[0]
//   "PUSH1 0x20",  // Push 32 (return size in bytes)
//   "PUSH1 0x00",  // Push 0 (memory offset to return)
//   "PUSH1 0x00",  // Push 0 (unused in RETURN context)
//   "RETURN"       // Return 32 bytes from memory[0]
// ]

// Analyze structure
const analysis = code.analyze();
console.log(`Valid: ${analysis.valid}`);           // Valid: true
console.log(`Instructions: ${analysis.instructions.length}`); // Instructions: 9
console.log(`Size: ${code.size()} bytes`);         // Size: 13 bytes

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Execution Flow

Initial Stack: []

PUSH1 0x05 → Stack: [5]
PUSH1 0x03 → Stack: [3, 5]
ADD        → Stack: [8]           // Pops 3 and 5, pushes result
PUSH1 0x00 → Stack: [0, 8]
MSTORE     → Stack: []            // Writes 8 to memory[0:32]
PUSH1 0x20 → Stack: [32]
PUSH1 0x00 → Stack: [0, 32]
PUSH1 0x00 → Stack: [0, 0, 32]
RETURN     → Returns memory[0:32] containing 8

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Parsing Individual Instructions

Use parseInstructions() for detailed instruction data: 
import { Bytecode } from 'tevm';

const code = Bytecode("0x6005600301");

const instructions = code.parseInstructions();
console.log(instructions);
// [
//   { opcode: 0x60, position: 0, pushData: Uint8Array([0x05]) },
//   { opcode: 0x60, position: 2, pushData: Uint8Array([0x03]) },
//   { opcode: 0x01, position: 4, pushData: undefined }
// ]

// Access push data
instructions.forEach(inst => {
  if (inst.pushData) {
    console.log(`PUSH at ${inst.position}: 0x${[...inst.pushData].map(b => b.toString(16).padStart(2, '0')).join('')}`);
  }
});

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Metadata Detection

Solidity compilers append metadata (typically 50-100 bytes) containing compiler version and IPFS hash: 
import { Bytecode } from 'tevm';

const deployedCode = Bytecode("0x608060..."); // Full deployed bytecode

// Check for metadata
if (deployedCode.hasMetadata()) {
  console.log("Contract includes compiler metadata");

  // Strip metadata for comparison
  const cleanCode = deployedCode.stripMetadata();
  console.log(`Original: ${deployedCode.size()} bytes`);
  console.log(`Stripped: ${cleanCode.size()} bytes`);
}
See hasMetadata() and stripMetadata().

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Extracting Runtime Code

Deployment bytecode includes initialization code that runs once. Extract just the runtime portion: 
import { Bytecode } from 'tevm';

const deploymentCode = Bytecode("0x608060...");

// Extract runtime bytecode (the code stored on-chain)
const runtimeCode = deploymentCode.extractRuntime();

console.log(`Deployment: ${deploymentCode.size()} bytes`);
console.log(`Runtime: ${runtimeCode.size()} bytes`);
See extractRuntime().

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EVM Instructions

The EVM has ~140 single-byte opcodes organized by category:
  • Arithmetic & Logic - ADD, MUL, SUB, DIV, AND, OR, XOR
  • Storage - SLOAD, SSTORE (persistent contract storage)
  • Memory - MLOAD, MSTORE (temporary execution data)
  • Control Flow - JUMP, JUMPI, JUMPDEST (loops, conditionals)
  • Contract Calls - CALL, DELEGATECALL, STATICCALL
  • Contract Creation - CREATE, CREATE2
  • System - SELFDESTRUCT, REVERT

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PUSH Instructions

PUSH1-PUSH32 (0x60-0x7f) embed 1-32 bytes of immediate data: 
import { Bytecode } from 'tevm';

// PUSH20 for Ethereum address (20 bytes)
const addressCode = Bytecode("0x73742d35Cc6634C0532925a3b844Bc9e7595f0bEb2");
// 0x73 = PUSH20
// Next 20 bytes = address

// PUSH4 for function selector (4 bytes)
const selectorCode = Bytecode("0x63a9059cbb");
// 0x63 = PUSH4
// 0xa9059cbb = transfer(address,uint256) selector

const instructions = selectorCode.parseInstructions();
console.log(instructions[0].pushData); // Uint8Array([0xa9, 0x05, 0x9c, 0xbb])

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Validation

Use validate() to check bytecode structure: 
import { Bytecode } from 'tevm';

const code = Bytecode("0x6001600201");

const validation = code.validate();
if (validation.valid) {
  console.log("Bytecode is structurally valid");
} else {
  console.error(`Invalid bytecode: ${validation.error}`);
}

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Resources

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Next Steps