If you spend any time in crypto, you will run into the term ERC-20 very quickly. It sounds technical, but the idea behind it is simple, and understanding it makes the rest of the token world a lot less confusing. Almost every token you can hold or swap on Base is an ERC-20 token, so it is worth a few minutes to learn what that means.
A shared rulebook for tokens
ERC-20 is a standard. Think of it as an agreed set of rules that a token contract promises to follow. The name comes from Ethereum Request for Comments, and 20 is just the number of that particular proposal. It was introduced in 2015 and became the template that most tokens on Ethereum, and on Ethereum layer 2 networks like Base, are built on.
Before the standard existed, every token project could invent its own way of doing things. That meant wallets and exchanges had to write special code for each token. ERC-20 fixed this by defining a small list of functions that every compliant token must include. Once a token follows those rules, any wallet, any exchange, and any block explorer already knows how to read its balance, move it, and display it. Nothing custom is required.
This is the quiet reason your wallet can show hundreds of different tokens without the developers having met a single one of those projects. They all speak the same language.
What the standard actually defines
An ERC-20 token is a smart contract, which is just a small program living on the blockchain. The standard says that program must expose a handful of functions. You do not need to memorize them, but seeing them once takes away the mystery.
- totalSupply: reports how many units of the token exist in total.
- balanceOf: reports how many tokens a given address holds.
- transfer: moves tokens from your address to someone else.
- approve and transferFrom: let you give another contract permission to move a set amount of your tokens on your behalf. This is the mechanism behind the approval step you see before a swap.
- allowance: reports how much a contract is still allowed to move.
There are also three descriptive fields: name, symbol, and decimals. The symbol is the short ticker, like USDC or DAI. Decimals matter more than they look. Most tokens use 18 decimals, which means the contract stores balances in tiny units and your wallet divides by a large number to show a friendly figure. USDC on Base uses 6 decimals instead. Your wallet handles this conversion for you, so you rarely think about it, but it is why a raw balance on a block explorer can look like an enormous number.
Why this matters when you swap
When you swap one token for another in a self-custody wallet, the whole process rides on these standard functions. The approval screen you sometimes see is the token contract recording that the swap contract may move a certain amount. The swap itself calls transferFrom to pull your tokens in and send the new ones out. Because every ERC-20 token behaves the same way, a swap app can support a token it has never specifically integrated, as long as that token follows the standard.
This is also why adding a custom token usually just works. You paste a contract address, and your wallet asks the contract for its symbol, decimals, and your balance. The standard guarantees those answers are there.
What ERC-20 does not promise
Here is the part that beginners often miss, and it is important. The ERC-20 standard describes how a token behaves technically. It says nothing about whether the token has value, whether the project is honest, or whether the code hides tricks.
A contract can follow the standard perfectly and still be a scam. Some tokens include extra code that blocks you from selling after you buy, or that lets the creator mint unlimited new supply, or that charges a hidden fee on every transfer. All of that can sit alongside a valid ERC-20 interface. The standard is a shared shape, not a seal of trust.
So treat ERC-20 compliance as table stakes, not a green light. Before holding anything beyond the well known tokens, check the contract address against a reliable source, look at the token on a block explorer, and be cautious with anything you cannot verify. Our guides on spotting scam tokens and adding custom tokens go deeper on this.
The short version
An ERC-20 token is any token on Base or Ethereum that follows a common rulebook for how balances are stored, moved, and approved. That shared standard is what makes wallets, swaps, and explorers able to handle thousands of tokens without special treatment for each one. It is a huge convenience and a foundation of how the whole ecosystem fits together.
Just remember the boundary. The standard tells you a token will behave predictably in a technical sense. It tells you nothing about whether the token is safe or worth holding. Those two questions are separate, and the second one is always on you to answer.