Deciphr Academy
Track 3 · Module 15 · Lesson 2 of 6 · 7 min read

How does a crypto price feed get a price onto a blockchain?

Short answer

A price feed is an oracle that keeps a current price on-chain for contracts to read.1 Chainlink's documentation says its feeds combine reports from several independent operators, and update when the price moves past a set threshold or a set time passes.2,3

When a push feed updatestimeBig move: deviation thresholdCalm: heartbeat updateDashed: price on exchangesSolid: price on the chain
Fig. 2. The real price moves all the time. The on-chain price only steps when it drifts past the threshold, or when the heartbeat time runs out.

A price, waiting on the chain

ethereum.org describes one kind of oracle that keeps a "data feed" that other contracts can read regularly.1 Its example is a feed of the latest ETH-USD price.1 In this module we call that a price feed.1

ethereum.org lists Chainlink's price feeds among the popular price oracles used in DeFi.1 We use Chainlink's own documentation below as a worked example of how one feed works.2

Many reporters, one answer

Chainlink's documentation says each feed is updated by several independent oracle operators.2 For crypto prices, it says the data comes from three or more price aggregators or market data vendors.4 Those use trading data from exchanges.4

The nodes share their readings over their own network and sign them. Then one combined report is sent to the chain.5 Sending one transaction instead of many saves a lot of gas, Chainlink says.5

The on-chain contract checks that enough nodes signed the report. Then it shows the median value as the feed's answer.5 If too few oracles respond, the answer is not updated.2 Combining many reports into one value like this is called aggregation.2

How to find a median

Sort the reports from lowest to highest and take the middle one. Five reports of $2,498, $2,500, $2,501, $2,503 and $9,000 have a median of $2,501. One wild report barely moves it. Their average would be $3,800.40.

When a feed updates

Chainlink's feeds do not stream prices.3 An update starts when one of two triggers fires, whichever comes first.2

  • Deviation threshold: the outside price has moved more than a set percentage away from the on-chain price.2
  • Heartbeat: a set amount of time has passed since the last update.2

When prices are calm, the heartbeat is what triggers updates.3 After a heartbeat is reached, there may be a short delay before the new round reaches the chain.3

Some heartbeats last several hours. So Chainlink tells apps to check the time of the latest answer.3 If the answer is too old, it suggests pausing, or switching to a backup mode, while you find out why.3

Settings vary from feed to feed. The same asset can have a different heartbeat and threshold on different blockchains.3 You can look them up on data.chain.link.3

Will the feed update?
  1. Work out how far the price has moved: (outside price − on-chain price) ÷ on-chain price × 100. Ignore a minus sign.
  2. If that is more than the deviation threshold, an update starts.
  3. If not, check the clock. If the heartbeat time has passed since the last update, an update starts.
  4. If neither, the on-chain price stays as it is.
Our viewA feed's settings are part of its risk. Before you rely on a feed, look up its threshold and heartbeat, and ask whether a price that old, or that far off, could hurt your users.
WatchOracles, in about two minutes. Captions are built in. Sources are listed at the end.
Sources
  1. Oracles. ethereum.org developer docs, page updated 26 June 2026.
  2. Decentralized Data Model. Chainlink documentation, page read 22 October 2026.
  3. What are Chainlink Data Feeds?. Chainlink documentation, page read 22 October 2026.
  4. Data Sources. Chainlink documentation, page read 22 October 2026.
  5. Offchain Reporting. Chainlink documentation, page read 22 October 2026.
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General education built from the publicly available sources listed above. Not financial, legal, tax or investment advice. Naming a company, project or regulator is not an endorsement either way. Last checked 2026-10-22. Terms and disclaimer.