Why did my crypto transaction fail?

A crypto transaction fails when the network accepts it into a block but the code it calls cannot finish, or when it never gets into a block at all. In the first case, everything the transaction tried to do is undone, but you generally still pay the fee. In the second case, nothing happens and no fee is paid. A block explorer shows which case you are in.

Why did my Ethereum transaction fail with out of gas?

Every Ethereum transaction carries a gas limit, a cap on how much computing work it may use. If the work needs more than that, the transaction stops partway. ethereum.org says the network then reverses every change, yet all the gas provided is still used up for the work done.

MetaMask's help pages note that some actions, such as buying an NFT, may need a higher limit than a simple transfer. OpenSea warns that changing gas limit settings can raise the chance of a failure.

What does transaction reverted mean?

Reverted means a smart contract refused to complete the action and rolled it back. The contract checked a condition, found it false and stopped. Typical reasons include:

• Slippage exceeded. Uniswap says a swap fails if the price moves past your slippage setting before it runs. Its default limit is 0.5%.
• Deadline expired. Uniswap swaps have a 30-minute deadline, which a transaction can miss if its fee was set too low.
• Someone got there first. MetaMask says reverts are common on NFT markets when another buyer completes the purchase first.
• Token rules. Some tokens charge their own fee or change balances automatically, and Uniswap says some of these types are not supported by its routers.

Is a failed transaction still charged gas?

Usually, yes, if it made it into a block. OpenSea explains that a reverted purchase costs the gas fee, not the price of the item, and that it cannot refund gas because it never receives it. Validators are paid for running the code, whether or not it succeeds.

There are exceptions. ethereum.org says a transaction rejected before it enters a block, for example one with a limit too low for even a basic transfer, uses no gas. Any gas left unused in a transaction that ran is refunded. A wallet warning that you lack the coin to pay the fee normally stops the send before it starts, as our guide to insufficient funds for gas explains.

MetaMask notes that a transaction can also be dropped and replaced, or sit pending on a low fee. Neither is a revert.

Why did my Solana transaction fail?

Solana bundles several steps, called instructions, into one transaction. Solana's documentation says that if any instruction fails, the whole transaction fails and all changes are reversed, and the fee is still charged. The base fee is 5,000 lamports per signature.

Each Solana transaction also carries a recent blockhash, a reference to a recent block, which stays valid for 150 slots. A transaction that has not landed by then expires and must be sent again. Swaps on Solana can fail on slippage in the same way as on Ethereum.