Resources
Links checked and pruned — several tools in the original list have shut down. Where something is gone, its replacement is named rather than the dead link being kept.
Learning and visualisation
| Resource | What it does |
|---|---|
| Blockchain demo | Interactive walkthrough of hashes, blocks and chains |
| evm.codes | Every opcode with current gas costs and an interactive playground |
| Ethereum developer docs | The reference introduction |
| Solidity by Example | Short, current, runnable examples |
Converters and encoders
| Resource | What it does |
|---|---|
| Ethereum Unit Converter | Wei, Gwei, ether |
| Keccak-256 | Hash a string; useful for deriving function selectors |
| HashEx ABI encoder | Build and decode ABI-encoded calldata |
| 4byte directory | Reverse a function selector to a signature |
cast from Foundry does all of these offline, which is preferable for anything
non-public:
cast --to-unit 1000000000000000000 ether
cast keccak "setCompleted(uint256)"
cast 4byte 0xfdacd576
cast abi-encode "constructor(address)" 0xADDRESS
Node providers
Faucets
Testnet faucets rotate frequently and rate-limit aggressively. Start from the official list for the network in question:
- Ethereum Sepolia — sepolia-faucet.pk910.de or a provider faucet tied to an Alchemy/Infura account
- Polygon Amoy — faucet.polygon.technology
Faucets for Ropsten, Rinkeby, Kovan, Goerli and Polygon Mumbai are dead along with those networks. See Deployment and verification.
Explorers
| Network | Explorer |
|---|---|
| Ethereum | etherscan.io |
| Sepolia | sepolia.etherscan.io |
| Polygon | polygonscan.com |
| Polygon Amoy | amoy.polygonscan.com |
| Many chains | blockscout.com |
Gas
Etherscan's gas tracker and Blocknative are current. GasNow was discontinued in 2021.
cast gas-price --rpc-url $RPC_URL
Security
| Resource | What it does |
|---|---|
| Smart Contract Weakness Classification | Catalogue of known vulnerability classes |
| Slither | Static analyser; run it in CI |
| Ethernaut | Vulnerability challenges, the fastest way to learn the failure modes |
| Damn Vulnerable DeFi | Harder, protocol-level challenges |
| Code4rena | Audit contest reports — read the findings |
pip install slither-analyzer
slither .
An audit is not a substitute for tests, and neither is a substitute for keeping the contract simple enough to reason about.
Marketplaces and platforms
Front-end odds and ends
- CSS Gradient
- SpinKit — loading animations
- Prism — syntax highlighting
- Framer Motion — animation
No longer available
Kept so that a reference to one of these in older notes is recognisable rather than puzzling:
| Gone | Replacement |
|---|---|
| GasNow gas estimation | Etherscan gas tracker, cast gas-price |
| ABDK toolkit encoder | HashEx, or cast abi-encode |
| Ropsten / Rinkeby / Kovan / Goerli faucets | Sepolia, Holesky |
| Polygon Mumbai faucet | Polygon Amoy faucet |
| Truffle, Ganache | Foundry, Hardhat — Development tools |
| web3.js | viem, ethers v6 — Dapp frontend |