Single Message Transforms for Confluent Platform

Single Message Transformations (SMTs) are applied to messages as they flow through Connect. SMTs transform inbound messages after a source connector has produced them, but before they are written to Kafka. SMTs transform outbound messages before they are sent to a sink connector. The following SMTs are available for use with Kafka Connect.


For a tutorial and a deep dive into this topic, see How to Use Single Message Transforms in Kafka Connect.

If none of the available SMTs provide the necessary transformation, you can create your own. See Custom transformations for more information.


This document contains SMT information that applies to all connectors, self-managed and fully-managed. However, some information linked to from this page may go to platform-specific docs that do not apply to fully-managed connectors. For instance, RegexrRouter and Custom SMTs are not currently available with managed connector SMTs.

Transform Description
Cast Cast fields or the entire key or value to a specific type (for example, to force an integer field to a smaller width).
Drop Drop either a key or a value from a record and set it to null.
ExtractField Extract the specified field from a Struct when schema present, or a Map in the case of schemaless data. Any null values are passed through unmodified.
ExtractTopic Replace the record topic with a new topic derived from its key or value.
Filter (Apache Kafka) Drop all records. Designed to be used in conjunction with a Predicate.
Filter (Confluent) Include or drop records that match a configurable filter.condition.
Flatten Flatten a nested data structure. This generates names for each field by concatenating the field names at each level with a configurable delimiter character.
HoistField Wrap data using the specified field name in a Struct when schema present, or a Map in the case of schemaless data.
InsertField Insert field using attributes from the record metadata or a configured static value.
MaskField Mask specified fields with a valid null value for the field type.
MessageTimeStampRouter Update the record’s topic field as a function of the original topic value and the record’s timestamp field.
RegexRouter Not currently available for managed connectors. Update the record topic using the configured regular expression and replacement string.
ReplaceField Filter or rename fields.
SetSchemaMetadata Set the schema name, version, or both on the record’s key or value schema.
TimestampConverter Convert timestamps between different formats such as Unix epoch, strings, and Connect Date and Timestamp types.
TimestampRouter Update the record’s topic field as a function of the original topic value and the record timestamp.
TombstoneHandler Manage tombstone records. A tombstone record is defined as a record with the entire value field being null, whether or not it has ValueSchema.
ValueToKey Replace the record key with a new key formed from a subset of fields in the record value.