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For example https://etherscan.io/uncles and https://etherscan.io/blocks_forked, what difference between them?

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Valid blocks that are not included in the main Ethereum chain because they were found a bit too late are still submitted to the network. Miners can include those blocks as "uncles" if they are not "older" (further away) than 7 blocks. They will receive a certain addition to the reward (a fraction) and the original miner of the uncle will also receive a reward which decreases with the "age" or "distance of the uncle.

It seems like the forked blocks page shows blocks that forked for any reason (e.g. and mostly because they were a bit too late) but which are NOT included as uncles later. The uncles page shows only those blocks that are actually recorded as uncles in the Ethereum chain.

While the list of uncles is complete because it can be read from the blockchain, it must be noted that the list of forked blocks depends on the connectivity of etherscan's nodes and, therefore, is not conclusive.

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  • Thanks! This is probably the clearest definition I've seen so far attempting to explain how forked blocks vs uncle's work. At a glance, it would then seem that you have to rely on checking a block's parent hash, and compare it to blocks you previously recorded to determine if you mistakenly included forked blocks as truth.
    – Josh Bowden
    Feb 4, 2022 at 18:17
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This is only a partial answer.

Here are some differences which I noticed when looking a the linked pages in your question:

Miner Reward. Forked blocks earned the miners a full reward (5 ETH + gas fees) while uncle blocks only earned them a fraction of that

Numbers As of today (July 7, 2017, 12.25 pm), there are only 15,584 forked blocks on the blockchain compared to 310,542 uncles. For some reason (that I hope someone else can explain), forked blocks are a lot less common.

Relationship Some forked blocks include uncles and others do not. Uncle blocks by definition all include one or two uncles.

Another big difference is that, after blockchain re-organization, forked blocks are excluded from the main blockchain (per the statement on the etherscan.io page you provided) while uncles can still be included / referenced on the blockchain, and that is in fact encouraged for a number of reasons which Vitalik explains in in this article:

Stale blocks in Ethereum can be re-included into the chain as “uncles”, where they receive up to 75% of their original block reward. This mechanic was originally introduced to reduce centralization pressures, by reducing the advantage that well-connected miners have over poorly connected miners, but it also has several side benefits, one of which is that stale blocks are tracked for all time in a very easily searchable database – the blockchain itself.

Having noted all these differences, and done some web research, I still could not get to the core difference between both types of blocks (i.e. forked and uncle). I hope others will help clarify further.

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  • So uncle block is a block which was found by another miner at same time, but how it includes in blockchain? how I understood, first miner who found a block, it goes to blockchain, second miner who found it also, just tracked in original that it has uncle at some position at which block was found uncle right?
    – DeV1doR
    Jul 10, 2017 at 8:54
  • Your answer may be a bit misleading. Forked blocks don't earn the miners any reward at all because they are not included in the Ethereum chain. The numbers shown on etherscan are not conclusive. Etherscan only shows those reorged and forked blocks that their own nodes see. If their nodes happen to be poorly connected to the rest of the network it would result in a high number of forked blocks and reorgs.
    – jotud
    Jan 11, 2018 at 18:58
  • If forked blocks are not included on the main chain, where does etherscan found those blocks? Is it true that every time you switch to a longer chain, the old one becomes a fork, while when someone else pushes a shorter one to you, that one becomes a uncle?
    – Justin Zhang
    Jul 5, 2021 at 23:42
  • @jotud it makes more sense to me that forked block doesn't earn any reward. But why it is valuable to show them on etherscan? Because it helps measure how much computing power is wasted?
    – Justin Zhang
    Jul 5, 2021 at 23:44
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Also note that since the upgrade to proof of stake, uncle blocks no longer exist.

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