How to read a blockchain explorer

Has this ever happened to you?

You send some BTC from one wallet to another. The coins disappear from wallet A but don't reappear in wallet B. You're feeling cold beads of sweat trickling down your spine. You run for help to the support team of wallets A and B only to get a short reply from an indifferent chatbot – 'Here's a link to your transaction on the blockchain. Please check the status there'.

Brilliant, and now what?

Usually, this problem only arises once, but it is a painful once, filled with anxiety and rage and googling absolute gibberish. Should you really know what an output value is, and if you do – will it help you get your money back?

To save you time and trouble, we've prepared a short guide. Now you'll be able to:

- Check on your transaction

- Estimate the time of arrival 

- Forget about the stuff you don't need.

Alons-y!

- What's up with my transaction?

First off, let's follow the link you were given. Most probably, it will lead you to some blockchain explorer – a tool that allows you to inspect transactions on the blockchain. There are plenty of such tools on the web. Even though they may look slightly different, they usually contain the same information.

(Copy and paste the transaction hash into the search bar if needed)

Let's dissect transaction details one by one.

The most important thing to focus on is Transaction status. It can read Confirmed or Unconfirmed. If it's Confirmed, you may also see the number of confirmations your transaction currently has. Why is it important?

Well, because it means how close your transaction is to being processed and finalised, i.e. how soon your coins will reach their destination. Transactions on the blockchain are generally irreversible. But in case something goes wrong, wallets usually credit funds when your transaction has 3–6 confirmations, just to be sure. One confirmation on the Bitcoin blockchain takes around 10 minutes, so your coins should reach you 30–60 minutes after your transfer has been added to the blockchain. 

See Confirming transactions on the Bitcoin blockchain for a deeper understanding of the blockchain technology and Proof of Work.

Okay, now let's suppose it's been an hour already, and your transaction still reads Unconfirmed. What to do?

- Has something gone wrong? 

Most probably, no. If it's been over 10 minutes, and your transaction still has no confirmations, chances are – there's a traffic jam. Unfortunately, sometimes the average confirmation time in the bitcoin network means nothing. Or rather, 

For the most popular cryptocurrency, Bitcoin's blockchain has a relatively small throughput. Sometimes, people would transact more than usual, so a queue of unconfirmed transactions will appear. 

To establish if this is the case, go straight to a mempool explorer (mempool is the place where unconfirmed transactions live), e.g. this one, to check how many transactions are currently waiting to be processed.

Although long processing times are inconvenient, this is not something that wallets can influence since it's not the wallets that process transactions but miners. What you can do to speed up the process is choose to pay a higher fee for processing your transaction. Alternatively, if you'd like to save on the fees and the time is unimportant, you can wait until there are fewer unconfirmed transactions.

Moving on to outputs now?

- Yes, why are there several outputs in the Recipient field if I only have one recipient?

Well, it's most probably due to the fact that...

- Thinking about it, I don't actually recognise the Sender's wallet address either, and the amount doesn't match. The bot must have given me the wrong link...

Good point. Both things are actually connected. Suppose you're using a custodial wallet* to manage your crypto and want to make a withdrawal. There's probably a handful of people withdrawing funds around the same time. What your wallet will do in this case is batch all these outgoing transactions into one to save on fees. 

Or it might be the opposite when there are multiple inputs for one output. This means that your withdrawal comes from different addresses.

*See What is Bitcoin, Wallet types

- Hmm, it says Change next to Recipient 2.

Or there's a third option :)

Bitcoin has a concept of change, but it differs from what we're used to. Suppose you have 10 BTC and want to send 5 BTC to your friend. You can't actually divide this amount and send part of it. Instead, you withdraw the whole amount, 1/2 of which goes to your friend, and the other 1/2 returns to a newly generated BTC wallet. That's your 'change'. 

The concept is different because the bitcoins you and your friend received are not the 'same' bitcoins you sent. What happens is that 10 BTC get destroyed and then recreated as 5 BTC + 5 BTC. This may seem strange, but this is how Bitcoin prevents double-spending.

- So we have ETA, Sender and Recipient and (maybe?) change? What about the stuff you don't need? I don't need it, do I?

Generally, it doesn't have any practical application unless you're running a blockchain analysis. But okay, let's take a quick glimpse so you don't have to google all those buzzwords separately.

The time and age are self-explanatory. So is the fee – this is what you pay to miners for processing your transaction. Incidentally, coinbase is also about miners, as it's the name given to the first transaction of each bitcoin block and is created by the block's miner themselves. Coinbase transaction aggregates all the transaction fees included in this block.

- Hash?

Now we level up. Basically, the hash is a value miners seek to complete/mine the newest block. To find the hash of the latest block, you need to know the hash of the previous block. Neighbouring blocks are interconnected, like in a chain, hence the blockchain.

See Confirming transactions on the Bitcoin blockchain

- Interesting. Tell me about Witness.

It's a feature of SegWit or Segregated Witness, a newer format for sending bitcoin transactions. To simplify, it redistributes and compresses data, thus making transaction size smaller, so you can fit more transactions in a block, making sending bitcoins cheaper. Witness No means an older – Legacy – format was used to send your transaction.

- What is RBF-enabled? 

Replace-by-Fee / RBF means that if your transaction is stuck in the long line of unconfirmed transactions, you can replace it with another version with a higher fee if your wallet supports this feature. If you see RBF-enabled No, your wallet doesn't support it. ('What if I cancelled the transaction?' you may ask. 'And then make another. Would it make it go through faster?' Alas, crypto transactions are irreversible and cannot be cancelled.)

- Locktime?

Also timelock. Means that the bitcoins can't be spent until some time in the future (e.g. if it's an investment).

The last 2 (or 3) may not apply to your case at all. But you're right: it's helpful to know what they mean to ensure you're not missing anything crucial.

And that's pretty much it – now armed with this knowledge, you'll know exactly where your transaction is and when the coins will appear in another wallet ✌️