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🌐 Web3🦊 Metamask

🦊 MetaMask

MetaMask is a browser and mobile wallet that lets you hold crypto, connect to dApps, and sign transactions and messages. It works with any EVM-compatible chain (Ethereum, Polygon, Arbitrum, Base, etc.).

📖 Full walkthrough: For a step-by-step intro to wallets, keys, gas, and DeFi basics, see MetaMask & Wallet Fundamentals in our weekly presentations.

🎯 What MetaMask Is (and Isn’t)

❌ MetaMask is NOT

  • A place where your coins “live”
  • A bank or custodian
  • The blockchain itself

✅ MetaMask IS

  • Key manager — Stores your private keys (encrypted with your password)
  • RPC client — Talks to blockchains via the provider (e.g. window.ethereum)
  • Signer — Signs transactions and messages so the network accepts them

The blockchain holds the state (balances, contracts). MetaMask only holds keys and sends signed transactions. If MetaMask disappeared, your accounts would still exist; you’d recover them with your seed phrase in another wallet.

🔑 Keys and Seed Phrase

ConceptDescription
Seed phrase12 or 24 words that derive all your keys. Back it up offline; never share it.
Private keyProves ownership of an address. Never share; required to sign.
AddressPublic identifier (e.g. 0x1234...). Safe to share; used to receive funds.

Whoever has the seed phrase controls every account derived from it. Use a strong password for MetaMask; it only encrypts the wallet locally and does not protect you if the seed is leaked.

🌐 Adding Networks and Using dApps

  • Add a network — Settings → Networks → Add network (or “Add a network manually”). You need the chain ID, RPC URL, and optionally block explorer.
  • Switch chain — Click the network dropdown in MetaMask; dApps can also request a switch via wallet_switchEthereumChain.
  • Connect a dApp — The dApp calls eth_requestAccounts; MetaMask shows a connect prompt. You can revoke site access in Settings → Connected sites.

For building dApps that connect to MetaMask, see EVM DApp (e.g. Wagmi & RainbowKit).

⛽ Gas and Fees

  • Gas — Units of computation; you pay in the chain’s native token (ETH, MATIC, etc.).
  • Gas price — Price per unit; higher usually means faster inclusion.
  • Gas limit — Cap on units; unused gas is refunded.

MetaMask lets you adjust gas (or use “market” estimates). For more on gas and DeFi flows, see MetaMask & Wallet Fundamentals.

🔐 Security Basics

  • Never share your seed phrase or private key (except in controlled dev/test setups).
  • Verify URLs — Phishing sites mimic MetaMask or dApp UIs; always check the address bar.
  • Revoke approvals — Use Revoke.cash  or similar to revoke token approvals when you no longer use a dApp.
  • Use a hardware wallet for large holdings; MetaMask supports Ledger and other devices.

🔗 Resources

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🌈 Wagmi and RainbowKit🧊 IPFS