HookOn Field

Specify which transaction types a Hook should be triggered on

Understanding the HookOn field

Each bit in this unsigned 256-bit integer indicates whether the Hook should execute on a particular transaction type. All bits are active low except bit 22 which is active high. Since 22 is ttHOOK_SET this means the default value of all 0's will not fire on a SetHook transaction but will fire on every other transaction type. This is a deliberate design choice to help people avoid bricking their XRPL account with a misbehaving hook.

Bits are numbered from right to left:

• bit 0 - right most, i.e. the least significant bit.
• bit 63 - the left-most, i.e. the most significant bit.

Examples (assuming a 256-bit unsigned integer type):

1. If we want to completely disable the hook:

C

~(1ULL << 22) /* every bit is 1 except bit 22 which is 0 */

2. If we want to disable the hook on everything except ttPAYMENT:

C

~(1ULL << 22) & ~(1ULL)

3. If we want to enable the hook on everything except ttHOOK_SET

C

0

4. If we want to enable hook firing on ttHOOK_SET (dangerous) and every other transaction type:

C

(1ULL << 22)

HookOn Calculator