Paste a definitions export and see what stops working on RabbitMQ 4.x: mirroring policies, transient queues, queue arguments that 4.3 refuses, and the quorum delivery limit that now drops messages. It also lists the traps that lose messages on any version, like a dead-letter exchange that routes nowhere. Every rule was checked against the RabbitMQ docs and a real RabbitMQ 4.3.6.
It runs in your browser; nothing is sent anywhere. Users, password hashes and permissions in the file are ignored. The export stays in this browser tab, so the other three tools pick it up without pasting it again.
Some 4.x changes live in the client code or in rabbitmq.conf, not in the definitions. Check these by hand:
basic_qos(global=True)) is a deprecated feature denied by default since 4.3, and quorum queues answer it with a channel error. Use per-consumer prefetch.durable=False and not exclusive are refused by 4.3 (the connection is closed). They only show up here if they existed when you exported.classic_queue.default_version = 1 in rabbitmq.conf stops a 4.0 node from starting.max_message_size).x-death header that a client sends when it republishes, so retry counters that relied on it start over. See the x-death decoder.rabbitmq-diagnostics check_if_any_deprecated_features_are_used exits non-zero if anything deprecated is in use.Sources: deprecated features list, 4.0 release notes, 4.3.0 release notes, quorum queues.