Even to the most seasoned crypto users, sending a transaction over a blockchain can be a truly nerve-racking event. For good reason. Crypto transactions cannot be reversed once sent. Not necessarily a problem in itself, except for the fact that a successful transaction is dependent on entering the correct address, which is unfortunate because cryptocurrency addresses couldn’t be less user-friendly if they tried. Each cryptocurrency employs its own address format. A brief glance at an address will often reveal the blockchain in question. Bitcoin addresses are generally between 26 and 35 characters in length. The oldest addresses all start with a “1”, which are known as legacy addresses. These can still be created, but newer addresses typically start with a “3”, indicating their more elaborate functionality. These two formats both use a Base-58 character set, meaning they use numbers, upper and lower case letters, with the exception of “0”, “o”, “l” or “I” to avoid confusion. Then there are also Segwit addresses, which always start with “bc1” but do not use Base-58 because they are entirely lower case: Legacy BTC address:         172YRdGzPqyXm9rm1EWKwPXTRsmcApoPq6 BTC Segwit address:          bc1q4nf39uxlddgptrhrlrddad2rt83rnex0dymcx8 Ethereum addresses always start with “0x” followed by 40 hexadecimal characters. This address format also holds for all smart contract tokens on the Ethereum blockchain. ETH address:                       0x7Ea90AF38397575A372e36bDc0F5970fB512FC7f Dogecoin addresses always start with a “D” followed by a number or upper case letter. They also use the Base-58 character set and are normally 34 characters in length. DOGE Address:                   D7wbmbjBWG5HPkT6d4gh6SdQPp6z25vcF2 Solana addresses also use the Base-58 character set and are typically 43 or 44 characters in length but other than that follow no particular format. This structure likewise holds for all smart contract tokens within the Solana ecosystem. Solana address:                  5axVea5zhqy2MWCooibzJjkYMHz3cvhPdgP7pVG7Sxee The above is far from exhaustive. The list of cryptocurrencies and their respective formats is a long and tedious one. The best thing a newer crypto user can do is to familiarise themselves with the blockchain they are interacting with. When sending a transaction to a certain address, the user has to ensure that every single character is correct. Fortunately, there are a number of in-built mechanisms to check the destination address, thereby preventing typos. Different cryptocurrencies have different ways of doing this, some more comprehensive than others, but they rely on variations of something called a checksum. Simply put, a checksum is a small piece of data derived from a larger piece of information that allows a system to check for errors, intentional or not. Their usage is ubiquitous even in traditional finance, for example with International Bank Account Numbers (IBAN). Bitcoin has always had a built-in checksum function which checks to see if the destination address actually exists. The function is designed to check for typos. By design, changing one or two characters in a valid address is extremely unlikely to result in another valid address, to the order of one in a several billion chance. This makes it all but impossible to accidentally send bitcoin to an address that is valid, but not the intended one. Of course, the check does nothing to ensure the transaction is not sent to an address that was used previously for example. Ethereum was not launched with such a tool. The reason being that the developers never intended for users to use raw hexadecimal address strings, but instead use unique domain names such as “DavesEtherWallet.eth”. The problem is that such domain names did not come into play until much later on, so the Ethereum foundation pushed an update to introduce a checksum function of its own in order to reduce mistakes. The difference between the two formats is readily apparent: Checksum address:             0x7Ea90AF38397575A372e36bDc0F5970fB512FC7f Non-checksum address:     0x7ea90af38397575a372e36bdc0f5970fb512fc7f The addresses above are one and the same, but the first one has been checksummed. Checksummed addresses use both upper and lower case letters whereas non-checksum addresses do not. When transacting on the Ethereum blockchain, always use the former whenever available. As mentioned above, there are ongoing attempts to simplify the process of transacting Ethereum by using domain names as opposed to raw addresses. These work in the same way as a URL, that is to say a human readable location on a network. Some cryptocurrencies, such as Solana, do not use a checksum function at all. Even when the cryptocurrency in question does use one, this does not necessarily mean that all wallet programmes take advantage of it. To avoid errors, users are encouraged to copy and paste instead of manually typing out addresses, starting with a test transaction first, and learning how to use blockchain explorers to check the validity of new addresses. A worthwhile question at this point is what happens to crypto sent to the wrong address? The short answer is that it is most likely lost forever. There have been instances of people wrongly sending funds to a wallet under someone else’s control, realising their mistake and then begging the unintended recipient to send the money back. The user can do this by sending a second transaction with a message encoded within it. Depending on how charitable the recipient is feeling, they may or may not honour the request. The other case is that the funds are sent to an address not currently under anyone’s control. It is important to understand that for a given cryptocurrency, the process of “creating” a new wallet is actually an exercise in generating a private key. The public address is merely a hash of that private key. If a user mistakenly sends money to an address to which there is no private key, the funds will simply sit there until the heat death of the universe. The number of total addresses is beyond astronomical. It is theoretically possible to generate a private key for a wallet that is already under someone else’s control, but the odds of doing so are infinitesimally small. This particularity of blockchain technology does in fact have a function. If there are addresses that cannot be accessed, or are extremely unlikely to be, then these can essentially be used as a cryptographic dustbin. Such addresses are referred to as burn addresses, because sending the coins or tokens there is akin to destroying them. Cryptocurrencies commonly have a default burn address, or even several. The wallets below contain over $80 million worth of Ethereum, as well as several hundred million dollars’ worth of various tokens. Ethereum burn addresses:  0x0000000000000000000000000000000000000000                                                   0x000000000000000000000000000000000000dEaD The ending string of characters on the second address is no coincidence. It is in fact possible to generate addresses with a certain string of characters that users may find amusing or meaningful. They are known as vanity addresses and it is possible to generate them with the appropriate software. Sending crypto for the first time can be a daunting process and the esoteric nature of crypto addresses is a significant contributor to this. That being said, underneath the enigmatic outer shell lies a wealth of information that crypto enthusiasts have every reason to delve into.