Predicates and Safety

Use validity predicates safely.

Predicates are inclusion conditions. They do not guarantee inclusion or successful execution.

Predicate Types

Type	Parameters
balance	address, op, value
storage	address, slot, op, value, optional mask
block_number	op, value
flashblock_index	op, value

The supported operators are <, <=, =, !=, >, and >=. Predicate values use 0x-prefixed hexadecimal strings.

Evaluation

Base evaluates predicates against the state immediately before the transaction would execute. If any predicate is false, the transaction remains pending.

An earlier transaction can change the balance or storage value that a pending transaction watches. The pending transaction can then become eligible in the same Flashblock.

Balance Example

Balance predicate

{
  "type": "balance",
  "params": {
    "address": "0x2222222222222222222222222222222222222222",
    "op": ">=",
    "value": "0x1"
  }
}

Storage Example

Storage predicate

{
  "type": "storage",
  "params": {
    "address": "0x2222222222222222222222222222222222222222",
    "slot": "0x7",
    "mask": "0xff",
    "op": "=",
    "value": "0x2a"
  }
}

Base compares (storage[address][slot] & mask) with value. Omit mask to compare the full storage word.

Block and Flashblock Position

Use block_number to target a block and flashblock_index to target a position within that Flashblock. Add separate predicates when both conditions must match. Valid flashblock_index values range from 1 through 10, inclusive; the corresponding hexadecimal values are 0x1 through 0xa.

Safety

A predicate does not simulate a transaction. Keep critical checks in the application call.

Predicates read raw storage. They cannot call view functions or evaluate computed values. Verify the target contract’s storage layout before using a storage predicate.

Do not use transaction placement as a source of randomness. Do not assume a zero-valued slot makes a CREATE2 address, proxy, or uninitialized contract safe to call.

Validity criteria are not recorded onchain. Do not include secrets in calldata or predicate values.