Developer tools

Calldata Decoder

Inspect an EVM function selector and decode parameters locally with an ABI you provide.

✓ Runs in your browser✓ No account✓ No wallet signature

Result

Your estimate

Decoded locally

Function selector0xa9059cbb

Function nameABI required

Add a matching ABI to decode parameter types and values.

Source: your inputsFreshness: calculated nowMethodology v1.0.0

Method

How this calculator works

The first four bytes are always shown as the selector.

JSON and human-readable ABIs are parsed as data and passed to Viem’s decoder; no user code is executed.

Decoded BigInt values are converted to readable strings before display.

Formula

The calculation

selector = first 4 bytes of calldata; remaining bytes are decoded against the matching ABI function

Example

A concrete scenario

ERC-20 transfer calldata beginning with 0xa9059cbb can be decoded as transfer(address,uint256) when that function is present in the supplied ABI.

Data provenance

Sources used

ViemLocal ABI decoding Solidity ABI specificationEncoding format

Privacy: Calculator inputs are processed locally in your browser. CoinCalcs does not receive or store these inputs. Theme and cookie preferences may be stored on this device.

Known limits

What this estimate cannot guarantee

A selector alone does not prove contract intent or safety.
Proxy contracts and overloaded functions can require the implementation ABI.
CoinCalcs does not query an external selector database in Phase 1.

FAQ

Questions about this tool

Is my ABI uploaded?

No. Decoding runs in your browser and the input is not sent to CoinCalcs.

Can I decode calldata without an ABI?

The tool can show the selector, but parameter decoding requires a matching function definition.

Does decoded calldata mean a transaction is safe?

No. Decoding improves readability but does not audit contract behavior or destination safety.

Last reviewed: July 18, 2026

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