What Is a Blockchain Oracle?

Blockchain Oracle Definition

Blockchain oracles are entities that connect blockchains to external systems, thereby enabling smart contracts to execute based upon inputs and outputs from the real world.

With the potential for hundreds of trillions of dollars worth of assets to move onchain, blockchain technology is transforming financial markets, global trade, insurance, gaming, and many other industries. Together, blockchains, smart contracts, and oracles underpin the verifiable web, where users can understand exactly what’s going on within an application and remain in control of their assets at all times. 

Oracles play a foundational role in the creation of the verifiable web, connecting blockchains that would otherwise be isolated to offchain data and compute, and enabling interoperability between blockchains. Initially, the Chainlink oracle network enabled the creation of the DeFi space and then grew to become the industry standard oracle solution for all of Web3. To date, Chainlink has enabled over $9T in transaction value. Now, Chainlink is collaborating with some of the world’s largest financial institutions, including Swift, the global messaging network for 11K+ banks, DTCC, the world’s largest securities settlement system processing $2+ quadrillion annually, and Australia and New Zealand Banking Group Limited (ANZ), a leading institution bank with $1T+ in AUM. 

With an entire suite of services that enable developers to build advanced, secure, cross-chain, and verifiable applications, the Chainlink platform is set to help scale blockchain technology to billions of users.

What Is an Oracle Network?

Oracles provide a way for the decentralized Web3 ecosystem to access existing data sources, legacy systems, and advanced computations. Decentralized oracle networks (DONs) enable the creation of hybrid smart contracts, where onchain code and offchain infrastructure are combined to support advanced decentralized applications (dApps) that react to real-world events and interoperate with traditional systems.

Blockchain oracles connect blockchains to inputs and outputs in the real world

For example, let’s assume Alice and Bob want to bet on the outcome of a sports match. Alice bets $20 on team A and Bob bets $20 on team B, with the $40 total held in escrow by a smart contract. When the game ends, how does the smart contract know whether to release the funds to Alice or Bob? The answer is it requires an oracle mechanism to fetch accurate match outcomes offchain and deliver it to the blockchain in a secure and reliable manner.

Solving the Oracle Problem

The blockchain oracle problem outlines a fundamental limitation of smart contracts—they cannot inherently interact with data and systems existing outside their native blockchain environment. Resources external to the blockchain are considered “offchain,” while data already stored on the blockchain is considered onchain. By being purposely isolated from external systems, blockchains obtain their most valuable properties like strong consensus on the validity of user transactions, prevention of double-spending attacks, and mitigation of network downtime. Securely interoperating with offchain systems from a blockchain requires an additional piece of infrastructure known as an “oracle” to bridge the two environments.

Centralized oracles
Blockchains cannot connect to real-world data and events on their own

Solving the oracle problem is of the utmost importance because the vast majority of smart contract use cases like DeFi require knowledge of real-world data and events happening offchain. Thus, crypto oracles expand the types of digital agreements that blockchains can support by offering a universal gateway to offchain resources while still upholding the valuable security properties of blockchains. Major industries benefit from combining oracles and smart contracts including asset prices for finance, weather information for insurance, randomness for gaming, IoT sensors for supply chain, ID verification for government, and much more.

Because the data delivered by oracles to blockchains directly determines the outcomes of smart contracts, it is critically important that the oracle mechanism is correct if the agreement is to execute exactly as expected.

Decentralized Oracles

Blockchain oracle mechanisms using a centralized entity to deliver data to a smart contract introduce a single point of failure, defeating the entire purpose of a decentralized blockchain application. If the single oracle goes offline, then the smart contract will not have access to the data required for execution or will execute improperly based on stale data.

Even worse, if the single oracle is corrupted, then the data being delivered onchain may be highly incorrect and lead to smart contracts executing very wrong outcomes. This is commonly referred to as the “garbage in, garbage out” problem where bad inputs lead to bad outputs. Additionally, because blockchain transactions are automated and immutable, a smart contract outcome based on faulty data cannot be reversed, meaning user funds can be permanently lost. Therefore, centralized oracles are a non-starter for smart contract applications.

Centralized oracles
Centralized oracles are a single point of failure

Truly overcoming the crypto oracle problem necessitates decentralized oracles to prevent data manipulation, inaccuracy, and downtime. A Decentralized Oracle Network, or DON for short, combines multiple independent oracle node operators and multiple reliable data sources to establish end-to-end decentralization.

DONs enable the creation of hybrid smart contracts, where onchain code and offchain infrastructure are combined to support advanced decentralized applications (dApps) that react to real-world events and interoperate with traditional systems.

Many Chainlink services, such as Chainlink Price Feeds, incorporate three layers of decentralization—at the data source, individual node operator, and oracle network levels—to eliminate any single point of failure. Chainlink Price Feeds already help secure tens of billions of dollars across smart contract ecosystems through this multi-layered decentralization approach, ensuring smart contracts can safely rely on data inputs during their execution.

Chainlink three layers of aggregation
Chainlink Price Feeds deploy three layers of decentralized aggregation

Types of Blockchain Oracles

Given the extensive range of offchain resources, blockchain oracles come in many shapes and sizes. Not only do hybrid smart contracts need various types of external data and computation, but they require various mechanisms for delivery and different levels of security. Generally, each type of crypto oracle involves some combination of fetching, validating, computing upon, and delivering data to a destination.

Input Oracles

The most widely recognized type of oracle today is known as an “input oracle,” which fetches data from the real-world (offchain) and delivers it onto a blockchain network for smart contract consumption. These types of oracles are used to power Chainlink Price Feeds, providing DeFi smart contracts with onchain access to financial market data.

Output Oracles

The opposite of input oracles are “output oracles,” which allow smart contracts to send commands to offchain systems that trigger them to execute certain actions. This can include informing a banking network to make a payment, telling a storage provider to store the supplied data, or pinging an IoT system to unlock a car door once the onchain rental payment is made.

Cross-Chain Oracles

Another type of oracle are cross-chain oracles that can read and write information between different blockchains. Cross-chain oracles enable interoperability for moving both data and assets between blockchains, such as using data on one blockchain to trigger an action on another or bridging assets cross-chain so they can be used outside the native blockchain they were issued on.

Compute-Enabled Oracles

A new type of oracle becoming more widely used by smart contract applications are “compute-enabled oracles,” which use secure offchain computation to provide decentralized services that are impractical to do onchain due to technical, legal, or financial constraints. This can include using Chainlink Automation to trigger the running of smart contracts when predefined events take place, computing zero-knowledge proofs to generate data privacy, or running a verifiable randomness function to provide a tamper-proof and provably fair source of randomness to smart contracts.

Hybrid smart contracts
Different types of oracles enable the creation of hybrid smart contracts

Oracle Reputation Derived From Onchain Performance History

The broad range of oracle services means reputation is key to choosing between oracle service providers. Reputation in blockchain oracle systems gives users and developers the ability to monitor and filter between oracles based on parameters they deem important. Oracle reputation is aided by the fact that oracles sign and deliver their data onto an immutable public blockchain ledger, and so their historical performance history can be analyzed and presented to users through interactive dashboards.

Reputation frameworks provide transparency into the accuracy and reliability of each oracle network and individual oracle node operator. Users can then make informed decisions about which oracles they want to service their smart contracts. Oracle service providers can also leverage their offchain business reputation to provide users additional guarantees of their reliability.

Blockchain Oracle Use Cases

Smart contract developers use oracles to build more advanced decentralized applications across a wider range of blockchain use cases. While there are a potentially infinite number of possibilities, below are the use cases with the most current adoption.

Decentralized Finance (DeFi)

A large portion of the decentralized finance (DeFi) ecosystem requires price oracles so smart contracts can access financial data about assets and markets. For example, decentralized money markets use price oracles to determine users’ borrowing capacity and check if users’ positions are undercollateralized and subject to liquidation. Similarly, synthetic asset platforms use price oracles to peg the value of tokens to real-world assets and automated market makers (AMMs) use price oracles to help concentrate liquidity at the current market price to improve capital efficiency.


Oracles enable non-financial use cases for smart contracts too such as dynamic NFTs—Non-Fungible Tokens that can change in appearance, value, or distribution based on external events like the time of day or the weather. Additionally, compute oracles are used to generate verifiable randomness that projects then use to assign randomized traits to NFTs or to select random lucky winners in high-demand NFT drops. Onchain gaming applications also use verifiable randomness to create more engaging and unpredictable gameplay experiences like the appearance of random loot boxes or randomized matchmaking during a tournament.


Insurance smart contracts use input oracles to verify the occurrence of insurable events during claims processing, opening up access to physical sensors, web APIs, satellite imagery, and legal data. Output oracles can also provide insurance smart contracts with a way to make payouts on claims using other blockchains or traditional payment networks.


Cross-chain oracles offer enterprises a secure blockchain middleware that allows them to connect their backend systems to any blockchain network. In doing so, enterprise systems can read/write to any blockchain and perform complex logic on how to deploy assets and data across chains and with counterparties using the same oracle network. The result is institutions being able to quickly join blockchains in high demand by their counterparties and swiftly create support for smart contract services wanted by their users without having to spend time and development resources integrating with each individual blockchain.


Hybrid smart contracts are advancing environmental sustainability by creating better incentives to partake in green practices through advanced verification techniques around the true impact of green initiatives. Oracles are a critical tool to supplying smart contracts with environmental data from sensor readings, satellite imagery, and advanced ML computation, which then allow smart contracts to dispense rewards to people practicing reforestation or engaging in conscious consumption. Oracles are also supporting many new forms of carbon credits to offset the impacts of climate change.

Chainlink stack
Chainlink’s growing collection of decentralized oracle services

Oracles extend the capabilities of blockchain networks by providing access to all the external resources required to harness useful and advanced hybrid smart contract use cases beyond simple tokenization. Similar to how the Internet brought forth a significant change in the way information is exchanged, oracle-powered hybrid smart contracts are redefining the way society exchanges value and enforces contractual agreements.

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