| name | selector-decode |
| description | Use when you encounter an EVM 4-byte function selector (0x followed by 8 hex chars at the start of calldata) and need to identify which function it represents, or when authoring a forbiddenSelectors policy rule. Provides a curated table of common selectors and a decoding workflow for unknown ones. |
selector-decode
A 4-byte selector is the first 4 bytes of EVM calldata. It is keccak256(canonicalSignature)[0:4] where canonicalSignature is the function name plus its parameter type list, with no spaces, e.g. transfer(address,uint256).
Curated table (most common in DeFi)
ERC-20
| Selector | Signature | Risk profile |
|---|
0xa9059cbb | transfer(address,uint256) | Direct outflow. Cap by destination + amount. |
0x095ea7b3 | approve(address,uint256) | Authorization to drain. Block infinite approvals; cap by spender + amount. |
0x23b872dd | transferFrom(address,address,uint256) | Pull payment. Often invoked by routers/protocols on behalf of the user. |
0x39509351 | increaseAllowance(address,uint256) | Quietly raises an existing approval. Treat like approve. |
0xa457c2d7 | decreaseAllowance(address,uint256) | Safe to allow; reduces exposure. |
0x70a08231 | balanceOf(address) | View only; no policy concern. |
ERC-721 / ERC-1155
| Selector | Signature | Risk profile |
|---|
0x42842e0e | safeTransferFrom(address,address,uint256) | NFT outflow. |
0x23b872dd | transferFrom(address,address,uint256) | NFT outflow (overlap with ERC-20). |
0xa22cb465 | setApprovalForAll(address,bool) | Critical. Grants spender control over ALL NFTs in the collection. Block by default. |
0x095ea7b3 | approve(address,uint256) | Per-token approval (uint256 = tokenId). |
Pausable / Ownable / Access control
| Selector | Signature | Risk profile |
|---|
0x8456cb59 | pause() | Pause contract. Often a remediation primitive. |
0x3f4ba83a | unpause() | Resume. |
0xf2fde38b | transferOwnership(address) | Hand over admin. Block unless explicitly allowlisted. |
0x715018a6 | renounceOwnership() | Brick contract. Block unless intentional. |
DEX routing (Uniswap V2/V3 representative)
| Selector | Signature | Notes |
|---|
0x38ed1739 | swapExactTokensForTokens(uint256,uint256,address[],address,uint256) | V2-style swap with deadline + min-out. |
0x414bf389 | exactInputSingle((address,address,uint24,address,uint256,uint256,uint256,uint160)) | V3 single-hop swap. |
0xc04b8d59 | exactInput((bytes,address,uint256,uint256,uint256)) | V3 multi-hop. |
0xfb3bdb41 | swapETHForExactTokens(uint256,address[],address,uint256) | ETH in, exact tokens out. |
Workflow when you see an unknown selector
- Read the selector from
intent.data slice [0:10] (the 0x plus 8 hex chars).
- Search 4byte.directory:
https://www.4byte.directory/signatures/?bytes4_signature=0x.... Multiple signatures collide on the same 4 bytes occasionally; pick the one consistent with the destination contract.
- Cross-check with the destination contract's verified ABI on the relevant block explorer (Etherscan, Basescan, Chainscan-Galileo).
- If still ambiguous and the call is high-value, recommend
REQUIRE_HUMAN_CONFIRMATION rather than ALLOW.
When authoring a forbiddenSelectors rule
Treat these as default-block for any treasury policy:
setApprovalForAll(address,bool) (0xa22cb465)transferOwnership(address) (0xf2fde38b)renounceOwnership() (0x715018a6)
Treat these as block-with-cap (use approvalCapByToken instead of a flat ban):
approve(address,uint256) (0x095ea7b3)increaseAllowance(address,uint256) (0x39509351)
Checking in code
src/core/selectors.ts exposes:
selectorOf(data) returns the lowercase 10-char selector or null if calldata is too short.decodeAddress(data, paramIndex) reads the paramIndex-th 32-byte word and returns the trailing 20 bytes as a hex address.decodeUint256(data, paramIndex) returns the paramIndex-th 32-byte word as a bigint.
When extending these helpers, keep them dependency-free (no ethers ABI coder) so the engine stays cheap to run.
