Server as a Function. We meant it literally — no annotations, no reflection, no container, no magic. Just immutable Kotlin functions you can read, test in-memory, and trust in production.
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Everything ships under a single BOM version, so it just works together — pull in only what you need.
| 🧩 Core | Servers, clients, routing, typesafe lenses, formats & a full testing toolkit. Zero dependencies. |
| 🤖 AI | LLM adapters, MCP and A2A — with Fakes so you can test AI integrations offline. |
| 🔌 Connect | Typed clients for cloud & SaaS APIs, each with a stateful in-memory Fake. |
| 🛡️ Pro & Enterprise | Premium modules, LTS, priority support and verifiable supply-chain security. |
- Testable — call your whole app in-memory, no server, no ports.
- Portable — swap Netty → Lambda → GraalVM with one line.
- Transparent — what you read is exactly what runs. Zero reflection.
- Proven — 5M+ downloads/month, in production since 2017.
val app: HttpHandler = { req -> Response(OK).body("hello ${req.query("name")}") }
app.asServer(SunHttp(9000)).start()We do our security homework in public — see our advisories and coordinated disclosure policy.
Apache 2.0 core · Built & maintained by http4k Ltd
Peace out. // the http4k team