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Bytecode

Low-level machine-readable instructions produced by compiling smart-contract source code for execution by a virtual machine.

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Definition

Low-level machine-readable instructions produced by compiling smart-contract source code for execution by a virtual machine.

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Why it matters

Smart-contract concepts are essential for understanding programmable blockchain applications.

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How it works

A compiler takes source code and performs a series of optimizations to output a hex string. This string contains opcodes like PUSH, POP, ADD, and SSTORE. When a transaction calls a contract, the EVM loads this bytecode into its execution environment and runs these opcodes in order.

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Real-world example

When you deploy a contract to Mainnet via Etherscan or Hardhat, the resulting hex data block in the transaction receipt is the bytecode deployed to the blockchain.

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Advantages

  • Highly efficient for machine execution
  • Immutable and tamper-proof
  • Ensures consistent behavior across different nodes

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Limitations

  • Difficult to read or debug
  • Reverse engineering is complex
  • Limited access to high-level logic

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Common misconceptions

  • People often think bytecode is the same as the Solidity source code, but it is actually the compiled output.
  • Some believe bytecode is always readable by humans, but it is meant for the machine, not for developers to edit directly.
Canonical knowledge ID: glossary:bytecode