> ## Documentation Index
> Fetch the complete documentation index at: https://docs.base.org/llms.txt
> Use this file to discover all available pages before exploring further.

# 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 checks a transaction before inclusion. If a 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

```json Balance predicate lines wrap expandable theme={null}
{
  "type": "balance",
  "params": {
    "address": "0x2222222222222222222222222222222222222222",
    "op": ">=",
    "value": "0x1"
  }
}
```

## Storage Example

```json Storage predicate lines wrap expandable theme={null}
{
  "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.

## 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.

State can change during block building. A condition can become true or false before inclusion.

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.