Chainlink

Chainlink provides decentralized oracle infrastructure: price feeds for DeFi pricing, VRF for provably fair randomness, Automation for scheduled/conditional on-chain execution, and CCIP for cross-chain messaging and token transfers.

What You Probably Got Wrong

• latestRoundData() returns int256, not uint256 — Price can be negative (e.g., oil futures in 2020). Always check answer > 0 before casting.
• Decimals vary per feed — ETH/USD has 8 decimals, ETH/BTC has 18 decimals, USDC/USD has 8. Always call decimals() or hardcode per known feed. Never assume 8.
• VRF v2 is deprecated — use VRF v2.5 — VRF v2.5 supports both LINK and native payment, uses requestRandomWords() with a struct parameter, and has a different coordinator interface. Most LLM training data references VRF v2.
• Staleness is not optional — A price feed can return a stale answer if the oracle network stops updating. You must check updatedAt against a heartbeat threshold. Feeds without staleness checks have caused protocol-draining exploits.
• roundId can be zero on L2s — On Arbitrum/Optimism sequencer feeds, round semantics differ. Do not rely on roundId for ordering on L2 feeds.
• CCIP is not Chainlink VRF — They are separate products. CCIP handles cross-chain messaging; VRF handles randomness. Different contracts, different billing.
• Automation renamed from Keepers — The product is now called Chainlink Automation, not Keepers. The interface names changed: KeeperCompatibleInterface is now AutomationCompatibleInterface.

Price Feeds

AggregatorV3Interface

The core interface for reading Chainlink price data on-chain.