Remix IDE Cheatsheet

Compiling

Use this Remix IDE reference while you build software engineering projects, review code for technical interview prep, or polish examples for a software engineer resume.

Opening the Compiler

Click the Solidity compiler icon (looks like an S) in the left icon bar. (Ctrl+S compiles the active file; Ctrl+Shift+S compiles it and runs the open script.)

Compiler Settings

Setting	Where	Notes
Compiler version	Version dropdown	Pick exact version or use `auto` (reads `pragma`)
Language	Language dropdown	Solidity (default) or Yul
EVM Version	Advanced → EVM Version	`prague`, `cancun`, `shanghai`, … — `default` tracks the newest fork the selected compiler supports
Optimization	Enable Optimization checkbox	Runs = 200 default; raise for deploy-once contracts, lower for frequently-called
Via IR	Advanced → Via IR	Enables the Yul intermediate pipeline (better optimization, slower compile)
Auto compile	Auto compile checkbox	Recompiles on every save (`Ctrl+S`)
Hide warnings	Hide warnings checkbox	Suppresses non-error diagnostics

Selecting a Compiler Version

pragma solidity ^0.8.24;   // Remix auto-selects >=0.8.24 <0.9.0

Auto: Remix reads the pragma and picks the latest matching release.
Manual: use the dropdown to pin an exact version (e.g., 0.8.24+commit.e11b9ed9).

First compile after selecting a new version downloads the compiler WASM — wait for the spinner to stop.

Compiling

Auto compile on — file saves trigger compilation automatically.
Manual — click the blue Compile \<filename\>.sol button.
Keyboard — Ctrl+S saves and (if Auto compile is on) compiles.

Reading Compiler Output

After a successful compile the button turns green. Expand the Compilation Details panel:

Tab	Content
ABI	JSON array of function/event signatures
Bytecode	Deployed bytecode (hex)
Runtime Bytecode	Code stored on-chain
Metadata	IPFS/Swarm hash, compiler settings
Function Hashes	4-byte selectors
Gas Estimates	Per-function upper-bound gas

Click Copy ABI or Copy Bytecode to clipboard.

Errors and Warnings

Color	Meaning
Red underline + red `✗`	Error — contract will not compile
Yellow underline + yellow `!`	Warning — compiles but potential issue
Blue squiggle	Info / style hint

Hover over underlined code for the full message. Errors also appear in the Terminal with file + line references.

Common Errors

Error	Cause	Fix
`Source file requires different compiler version`	`pragma` mismatch	Change compiler version in dropdown
`Identifier not found`	Missing import	Add `import` statement
`Stack too deep`	Too many local variables	Use `--via-ir`, split function, or use memory struct
`Contract size limit`	Bytecode > 24 KB	Split into libraries, optimize, or enable `--via-ir`
`SPDX license identifier not provided`	Missing header	Add `// SPDX-License-Identifier: MIT`

Optimization Examples

// For a contract deployed once and called many times (e.g., ERC-20)
// Optimizer runs: 200 (default) — good balance

// For a factory deployed rarely but instances called often
// Optimizer runs: 1 (minimize deploy cost)

// For a library called millions of times
// Optimizer runs: 100000 (minimize runtime cost)

Set runs in Advanced Configurations → Optimization → Runs.

Exporting Artifacts

After compile, artifacts (ABI + bytecode JSON) are written to artifacts/<ContractName>.json in the workspace. Use these with ethers.js / web3.js:

const artifact = require('./artifacts/Hello.json');
const factory = new ethers.ContractFactory(artifact.abi, artifact.bytecode, signer);