# Set field

Writes a value into a field of the event type.

| Configuration | Content                                                                                             |
| :------------ | :---------------------------------------------------------------------------------------------------- |
| Destination   | field of the event type                                                                             |
| Value         | [fixed value or expression](/en/rules/actions/#fixed-value-or-expression), validated according to the field type |

It is the most common action, applied to cases such as flagging a transaction for review, classifying an event, or recording the risk band assigned to it.

```
Condition:  $amount > 10000 and $issuer_country != "BR"
Action:     Set field → review = "true"          (fixed value)
```

In expression mode, the value written comes from another field, from a temporary variable, or from a join, which makes it possible to carry a result computed during the rule into the event:

```
Condition:  $amount > 0                    → Run analysis: bot
Condition:  %bot.triggered == true         → Set field: bot_score = %bot.score   (expression)
```

The value is validated when the rule is saved, according to the destination field's rules: a numeric field does not accept text, a text field respects the configured size. Fields reserved by the platform (starting with `_`) cannot be filled in by an action.

When the destination is a boolean field, the fixed value is chosen from a list with the field's own two labels: you select **Blocked**, not `true`. To copy a boolean from somewhere else, such as `%bot.triggered`, use expression mode.

If two conditions fill in the same field, the last one executed wins.