Chainlink's $LINK token does more than move value between wallets. Because of the way it is built, a single LINK transfer can also carry instructions for the smart contract receiving it. How
Chainlink's $LINK token does more than move value between wallets. Because of the way it is built, a single LINK transfer can also carry instructions for the smart contract receiving it.
Most tokens on Ethereum follow ERC-20, the basic standard for sending and holding tokens. @chainlink's LINK follows ERC-677, which builds on that base. According to Chainlink's documentation, the LINK token is an ERC-677 token that inherits functionality from the ERC-20 standard and allows token transfers to contain a data payload.
That extra data powers a function called transferAndCall. It allows tokens to be transferred whilst also triggering logic in the receiving contract within a single transaction. In practice, LINK can move to another smart contract and tell that contract what to do next in the same step.
The design avoids a multi-step process. As an Immunefi explainer notes, with the regular ERC-20 standard, a user has to approve and then call the contract in multiple steps, while ERC-677 allows both in a single transaction. The same explainer says ERC-677 tokens can be stored in any ERC-20-compatible wallet, so the added feature does not break compatibility with existing tools.
Chainlink's original request model used this feature to pay an oracle and send the request in one step. Chainlink's documentation describes how the client constructs and makes a request to a known Chainlink oracle through the transferAndCall function, implemented by the LINK token. That single-oracle setup is now retired, but transferAndCall still works on every LINK transfer.
LINK also has its own smallest unit, much like wei for Ether. The smallest denomination of LINK is called a Juel, and 1e18 Juels equal 1 LINK, similar to Wei for ETH. The name honours Ari Juels, the Cornell professor who co-authored the first Chainlink white paper. He co-authored it in 2017 with Sergey Nazarov and Steve Ellis, and the Juel is named in his honor.
For developers, the unit matters in practice. Chainlink's documentation on token units explains that an 18-decimal token such as LINK or ETH uses 10^18 base units per token, so onchain values must be set in the smallest unit rather than whole tokens.
The pay-and-call pattern remains a defining technical feature of $LINK, and it is one reason the token is often cited as an example of ERC-677 in use.
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