I have read the Oraclize documentation: https://docs.oraclize.it/#home

and similar topic like: How do oracle services work under the hood

But is still have a question, take this example: I have a simple smart contract that makes a Oraclize call (or an API call) to a data source. Every miner that need to run the smart contract for reach consesus, so every of them will do the Oraclize call? or the call will always be done one time? If every of them do the call it's possibile that the result of call is different, for example if the call is to a financial data source.

1 Answer 1


No, that's not how Oraclize works.

  1. You send an API call to Oraclize contract
  2. Oraclize has a node monitoring the contract
  3. Oraclize does the query off-chain
  4. Oraclize sends a tx calling your _callback function with the result of the API call

So none of the nodes or miners call an external service, Oraclize puts the data on the chain once

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