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Decoding a sample transaction input data field
This guide walks through reading the input data of an Ethereum transaction, using a transfer call as the worked example. Each step is a decision that makes raw hexadecimal understandable and checkable.
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Step one: separate selector from arguments
Take a standard token transfer. The input data begins with 0x, followed by eight hexadecimal characters, the function selector, and then arguments padded to thirty-two bytes each. In the example, a selector of a9059cbb marks a transfer function. Everything after it is argument data. Draw a line after those first eight characters and split the remainder into equal sixty-four character blocks. This single decision removes most of the visual noise. Before decoding anything, confirm the total length matches the selector plus whole blocks, because an odd length usually signals a copying error or truncated paste.
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Step two: match blocks to the interface
Next, decide which interface description governs the call. For a transfer function the description lists two parameters: a recipient address and an amount. Assign the first block to the address and the second to the amount. The address occupies the last forty characters of its block, with leading zeros as padding. The amount is a large hexadecimal integer. Record each assignment in a small table with parameter name, type and raw block. If the interface description is unavailable, label blocks as unknown instead of guessing, since a wrong interpretation is worse than an honest gap in your notes.
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Step three: convert, verify and record
Finally, convert the amount from hexadecimal to a decimal integer, then apply the token's decimal places to get a human figure. If the amount block reads as one thousand in hexadecimal terms and the token uses six decimals, the displayed value is a tiny fraction of one unit. Verify by comparing against the transaction details shown by a block explorer you trust. Write down the selector, the recipient, the raw and converted amounts, and the source of the interface description. That record lets a colleague repeat your reading and catch any slip quickly.