Paste a Java class, pom.xml/build.gradle, or application.properties/.yml. Pick your upgrade path and the analyzer flags what breaks — and, unlike a blind javax→jakarta replace, it tells you which javax.* imports are JDK packages you must leave alone.
Everything runs in your browser — nothing is uploaded. Mixed input is fine; each rule set only fires where it applies.
javax.* import as MIGRATE (Jakarta EE 9) or KEEP (JDK). Keeps javax.sql, javax.crypto, javax.net.ssl, javax.naming, javax.management, javax.xml.parsers/transform/xpath, javax.transaction.xa, javax.annotation.processing, javax.security.auth.WebSecurityConfigurerAdapter, antMatchers, authorizeRequests, @EnableGlobalMethodSecurity), and deprecated Hibernate 6 dialects (versioned + InnoDB/MyISAM).spring.redis.*, spring.data.cassandra.*, server.max-http-header-size, spring.datasource.initialization-mode, spring.sleuth.*, management.metrics.export.*, spring.session.store-type, spring.batch.job.names, SAML2 identity-provider→asserting-party, httptrace→httpexchanges.HttpTraceRepository→HttpExchangeRepository, type-level @ConstructorBinding, @EnableBatchProcessing, Elasticsearch RestHighLevelClient.mysql-connector-java→com.mysql:mysql-connector-j, git-commit-id plugin, javax.* Java EE artifacts.spring-boot-starter-web→-webmvc, -aop→-aspectj, -oauth2-*→-security-oauth2-*, Undertow removed.EnvironmentPostProcessor, BootstrapRegistry, @EntityScan, @PropertyMapping, TestRestTemplate, Spring's @Nullable→JSpecify; hibernate-jpamodelgen→hibernate-processor.com.fasterxml.jackson→tools.jackson (annotations excepted), @JsonComponent→@JacksonComponent.@MockBean→@MockitoBean, @SpyBean→@MockitoSpyBean, MockitoTestExecutionListener removed.Rest5ClientBuilderCustomizer, Kafka StreamsBuilderFactoryBeanConfigurer, RabbitMQ retry customizers.spring.session.redis.*, spring.data.mongodb.*→spring.mongodb.* (incl. ssl/protocol/uuid), management.health.mongo.*→mongodb, spring.jackson.read.*, spring.dao.exceptiontranslation.*, spring-authorization-server.version…Rules verified against the official Spring Boot 3.0 and 4.0 migration guides. It reads imports, config keys, starter artifactIds and well-known annotations — not fully-qualified inline usages — and does not resolve deeply nested YAML.