Why doesn't MQTT have its own Express? Introducing mqttkit

mqttkit: Elysia-style application framework for MQTT An ordered middleware pipeline, typed topic routes, MQTT 5 RPC, and auto-generated AsyncAPI docs — sitting on top of any MQTT broker. If you've ever built a serious MQTT backend in Node, you've probably written this code at least once: client . on ( ' message ' , ( topic , payload ) => { if ( topic . startsWith ( ' devices/ ' ) && topic . endsWith ( ' /events ' )) { const uid = topic . split ( ' / ' )[ 1 ] // ad-hoc auth check // ad-hoc JSON.parse + validation // ad-hoc error handling // ad-hoc metrics // ... } else if ( topic . startsWith ( ' server/ ' )) { // ... } }) That's the MQTT equivalent of writing an HTTP server with http.createServer((req, res) => { if (req.url === '/users') ... }) . We solved that pattern for HTTP a decade ago with Express, Koa, Fastify, and more recently Hono and Elysia. For MQTT, we haven't. That's the gap mqttkit is filling. The design choice: don't reimplement the protocol There are already excellent MQTT brokers in the Node ecosystem — most notably Aedes , which handles CONNECT, SUBSCRIBE, PUBLISH, QoS, retain, sessions, persistence, and MQTT-over-WebSocket. EMQX and Mosquitto cover production scale. None of these need replacing. What's missing is the application layer — the part where you ask: How do I declaratively say "this topic requires this auth check"? How do I validate payloads with the same schema I already use for HTTP? How do I do MQTT 5 request/response without writing correlation-id bookkeeping? How do I get AsyncAPI docs for free? How do I attach Prometheus / OpenTelemetry without lifting broker internals? mqttkit is purely that layer. It plugs into Aedes via @mqttkit/aedes , but the broker is just an adapter — you can write your own for EMQX, NanoMQ, or any other broker. What the code looks like import { aedes } from ' @mqttkit/aedes ' import { MqttApp , router } from ' @mqttkit/core ' import { z } from ' zod ' const app = new MqttApp < { principal ?: { uid : string