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I'm only getting started with my knowledge of Blockchains, but one thing has me confused.

If I were to build a Dapp offering a service for users, such that users don't have to pay to use the service, how can the transaction fees from executing the computation be paid for?

If a way around this was to only show data (i.e. so nothing is being written to the Blockchain, only read), would that have a computation cost? Does reading data count as a transaction?

Thank you in advance for your help. Please don't hesitate to correct any of the above.

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Reading from the blockchain is free. Writing to the blockchain is not.

Why? Writing data to the chain requires that data to be saved in a block. Miners have to mine that block, and mining has costs (electricity etc).

If you were so inclined you could write a contract, send it some Ether, and have your contract functions send the transaction sender some of that Ether when they call the function. I.E Subsidize people using your contract.

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    It's perhaps worth noting that this refund solution doesn't help you with the "cold start" problem of helping a new user issue a transaction for free. They still need some ether in their account to pay for the gas before being reimbursed. – carver Aug 11 '17 at 18:33
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This isn't possible in production Ethereum right now. The end user must pay for the gas costs to run a transaction with your service.

However in a few years, Serenity is scheduled to go live with EIP 101 (draft). It would allow contracts to pay gas for the caller, among many other features.

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