Kafka Config Upgrade Checker

Paste a Kafka config, pick the version you run and the one you are moving to, and see what changes. The settings that stop existing, the values that stop being accepted, and the defaults that move under a setting you never wrote down.

Kafka's own ConfigDef for all 16 releases from 2.5 to 4.1, compiled into this page. The kind is detected from the settings you paste and the report says which one it used, so override it if the guess is wrong.

Paste below, or drop a file anywhere on this panel

Or drop a file anywhere on this panel. Nothing is uploaded: the analysis runs in this tab.

The answer appears here

Paste on the left and press Check upgrade. Nothing leaves this tab.

Common mistakes

These are the ones that fail silently. The config is accepted, nothing raises an error, and the consequence arrives later.

  1. Upgrading brokers and clients at the same time

    The documented order is brokers first, then inter.broker.protocol.version, then clients. Doing it together turns one rollback into two.

    Instead:Follow the documented sequence and pause between steps.

  2. Leaving inter.broker.protocol.version pinned after the upgrade

    The cluster runs on the old protocol indefinitely and none of the new features work, which then looks like the upgrade failed.

    Instead:Raise it as a separate deliberate step once every broker is on the new version.

  3. Assuming a removed setting fails loudly

    Some removed settings are ignored rather than rejected, so the broker starts and behaves differently from the config you wrote.

    Instead:Check for removals against the target version before the upgrade.

Why a Kafka upgrade breaks a config nobody edited

Three separate things change between releases, and only one of them is visible in a diff of your own files.

A setting stops existing

Kafka removes configs, and the client does not tell you in a way anybody notices. It logs one line at WARN, "The configuration 'x' was supplied but isn't a known config.", and starts. Whatever that setting was tuning goes back to the built-in behaviour. There is no error, no failed health check and nothing in a diff, because your file did not change. 4.0 removed the most at once, since it dropped ZooKeeper mode entirely.

A default moves under a setting you never wrote down

Kafka 3.0 turned the idempotent producer on by default, which changed acks from 1 to all and enable.idempotence from false to true. A producer config that mentioned neither got different durability and different throughput on the same file. 3.0 also raised the consumer session.timeout.ms from 10 to 45 seconds, and 4.0 changed the producer linger.ms from 0 to 5 milliseconds, which moves the latency profile of every default producer. None of these appear in a diff of your config, and all of them appear here.

A value stops being accepted

This is the one that does fail loudly. ConfigDef validates a value against its permitted set and throws a ConfigException at startup rather than ignoring it, so a value that was valid on the old release stops the client dead on the new one. It is the least common of the three and the easiest to fix, because the error names the setting.

Deprecated is not the same as removed

Kafka's ConfigDef carries no deprecation flag, so the only signal is the wording of the documentation. Where a setting's own description says it is deprecated, that is reported as planned work rather than a blocker, along with the release the documentation names for its removal. It is read narrowly on purpose: several settings describe some *other* thing as deprecated while being the recommended replacement themselves, and flagging those would tell you to stop using the setting you should be moving to.

What this cannot see

It reads a .properties file against Kafka's ConfigDef. It does not know your broker count, your topics, your actual throughput or which client library version you run, and it cannot tell you whether a default change matters for your workload, only that it happened. It also cannot see settings belonging to interceptors, metrics reporters or Connect plugins, and it says so rather than calling them mistakes. For the runtime questions, the producer and consumer linters on this site answer a different half.

More kafka tools

Kafka Confluent Wire Format Decoder The five junk bytes in front of your payload Kafka Key to Partition Mapper Which partition does this key land on? Kafka Topic Name Validator Legal, risky, or 249 characters too long? Kafka Replication Safety Checker How many brokers can you lose Kafka Producer Config Linter Will it start, and will it lose a record? Kafka Message Payload Decoder The first five bytes are usually not data Kafka Connect Source Connector Generator tasks.max is a ceiling, not a count Kafka Connect Sink Connector Generator A dead letter queue with no context headers is a pile of records Kafka Connect SMT Chain Builder The order is the transforms list Kafka MirrorMaker 2 Config Generator It renames every topic by default Kafka Partition Reassignment Generator The throttle is not optional Strimzi Kafka Resource Generator Without the cluster label, nothing happens Kafka mTLS Config Generator The certificate is the identity Kafka Schema Registry Config Generator The compatibility direction is your deployment order Kafka Exactly-Once Config Generator Half of it is worse than none Kafka Broker and KRaft Config Generator The internal topics that break a one-broker cluster Kafka Quota Generator Byte rates are per broker, not per cluster Kafka Streams Config Generator application.id is four things at once Kafka Connect Worker Config Generator Security three times, or the tasks fail Kafka Retention and Unit Converter log.retention.hours does not take milliseconds Kafka Timestamp Converter Two sentinels and two meanings Kafka .properties to YAML Converter Dotted keys stay flat Kafka Streams Internal Topic Predictor Create them before Streams does Kafka ACL Generator The grant you forgot is on another resource type Kafka Topic Config Generator min.insync.replicas is the one that matters Kafka client.properties Generator The file every CLI tool asks for Kafka Producer Config Generator No password field, on purpose Kafka Consumer Config Generator The commit mode decides the semantics Kafka Disk and Retention Calculator retention.bytes is per partition Kafka Partition Count Calculator The number you can never reduce Kafka Cluster Sizing Calculator The traffic no client metric shows Kafka Consumer Lag Catch-Up Calculator Whether it ever clears, not just when Kafka Producer Batching Calculator linger.ms=0 still batches Kafka Segment and Index Sizing Why retention.ms is a lower bound Kafka Rebalance Duration Estimator What a rolling restart really costs Kafka Cost Estimator Your rates, so nothing goes stale Kafka Config Explorer by Version The answer depends on the release Kafka Default Config Reference What moved under a config you never edited Kafka OAuth Bearer Token Decoder Will Kafka accept it, and can it refresh Kafka Record Header Viewer Headers are a list, not a map Kafka Topic Regex Subscription Tester Kafka matches the whole name Kafka ACL Permission Matrix Viewer DENY beats every ALLOW Kafka Connect Config Validator The mistakes that raise no error Kafka Consumer Group Id Validator Which broker coordinates the group Kafka Partition Assignment Visualizer Leadership is the load, not replicas Kafka Consumer Assignment Visualizer The three assignors disagree Kafka ZooKeeper to KRaft Config Converter The authorizer class nobody changes Kafka Config to Strimzi Half of it belongs elsewhere Kafka Docker Compose Generator (KRaft) Reachable from inside and outside Kafka JAAS Config Decoder The line that stops SASL working Kafka CRC32C Calculator Which CRC, over which bytes Kafka Config Diff Which change actually changed something Kafka Consumer Config Linter Why the group rebalances, and where the records went Kafka Avro Schema Validator The defaults Avro accepts and rejects Kafka Schema Compatibility Checker What the registry will say, before you ask it Kafka Avro Schema Diff Which direction each change breaks Kafka Compression Comparison Measured on your bytes Kafka Delivery Semantics Exactly-once has a consumer half Kafka ksqlDB Query Builder It looks like SQL and the rules are not Kafka Connect SMT Predicate Tester negate reads backwards Kafka Streams Topology Viewer Count the repartitions Kafka Connect Pipeline Visualizer The order things really run in Kafka Protobuf Binary Decoder Works without the .proto Kafka Protobuf JSON Converter Why your JSON does not round-trip Kafka Protobuf to Avro Schema What does not survive the conversion Kafka Avro Binary Decoder Wrong schema, no error Kafka Avro JSON Converter Why the console producer rejects your line Kafka Avro Sample Data Generator Records that actually serialize Kafka JSON to Avro Schema What JSON cannot tell you Kafka JSON Schema to Avro What does not survive the conversion Kafka SASL JAAS Generator One login module, four syntaxes Kafka CLI Command Builder kcat is librdkafka, not Kafka

Elsewhere on the site

Terraform Validator & Formatter Kubernetes YAML Generator Kubernetes YAML Validator AWS IAM Policy Validator & Analyzer