Remix IDE Cheatsheet

Compiling

Use this Remix IDE reference while you build software engineering projects, review code, or refresh the syntax you reach for most.

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);