ABI Decoder & Encoder

How to use the ABI Decoder & Encoder

1. Paste a contract ABI — JSON or human-readable signatures — into the Contract ABI box.
2. Choose a tab: Decode Calldata, Encode Function, or Decode Event Log.
3. Fill in the calldata, function + arguments, or topics + data for that tab, then click the action button.
4. Copy the decoded function/event name and arguments, or the generated calldata, from the output panel.
5. Don't have the ABI? On the Decode Calldata or Decode Event Log tab, click Look up signature online to query 4byte.directory by the selector alone. On Decode Calldata, picking a candidate fills in the ABI and decodes right away. On Decode Event Log, candidates are shown for reference — add the event to the ABI yourself, marking the correct parameters indexed, to decode it.

All three tabs share the same ABI input, so you can switch between decoding and encoding the same contract without re-pasting it.

See it in action

Many online calldata tools handle only one direction — decoding or encoding, not both from the same ABI. Here's a real round trip: encoding an ERC-20-style transfer call, then decoding the result straight back against the same ABI.

ABI:

function transfer(address,uint256) returns (bool)

Encode Function — these arguments:

["0x1234567890AbcdEF1234567890aBcdef12345678", "1000000000000000000"]

produce this calldata:

0xa9059cbb0000000000000000000000001234567890abcdef1234567890abcdef123456780000000000000000000000000000000000000000000000000de0b6b3a7640000

Decode Calldata — pasting that same calldata back in against the same ABI recovers:

{
  "functionName": "transfer",
  "args": [
    "0x1234567890AbcdEF1234567890aBcdef12345678",
    "1000000000000000000"
  ]
}