Transports

stdio (the default)

npx klaridian generate --spec ./api.yaml --out ./my-server

The generated server talks to its client over standard input/output. This is what most MCP clients (Claude Desktop, Claude Code, and others) expect when they spawn a server as a local process. Use this unless you have a reason not to.

streamable-http

npx klaridian generate --spec ./api.yaml --out ./my-server \
  --transport streamable-http --port 3000

The server listens on a network port instead. Use this when the server needs to run somewhere other than the client's own machine—for example, behind OAuth (see OAuth 2.1). This requires streamable-http—it doesn't work with stdio.

Built-in test client

A streamable-http server serves a small, dependency-free HTML test client at its root (TypeScript target). With the server running, open http://localhost:3000/ (or whatever --port you chose) in a browser: it connects to the server's /mcp endpoint, lists the tools the server exposes, and lets you call any one with a JSON arguments field. Because it just asks the running server what it can do, it works the same regardless of how the server was generated—per-tool or code-mode. MCP itself stays on /mcp—the client is only served on GET /. The client's source is vendored in the generated project (src/test-client.ts), so you can read, edit, or remove it.

Deploying behind a public host

The --port you pass at generation time is only the default. The generated streamable-http server reads three environment variables at runtime, so one build runs unchanged across environments:

Variable	What it does	Default
`PORT`	The port to listen on. Takes precedence over `KLARIDIAN_PORT` and the generated default. Most platforms (Cloud Run, Render, Railway, Heroku) inject this automatically.	the `--port` value
`KLARIDIAN_BIND_HOST`	The network interface to bind. Set to `0.0.0.0` inside a container or PaaS so the server accepts traffic from outside its own loopback.	`127.0.0.1`
`KLARIDIAN_ALLOWED_HOSTS`	Comma-separated hostnames allowed in the `Host` header. By default only localhost is accepted (per the MCP spec's DNS-rebinding protection). When the server is reached through a public hostname—`myapp.fly.dev`, `name.workers.dev`, a custom domain—add it here, or every request is rejected with `403 Invalid Host`.	localhost only

For example, deploying to a host that serves myapp.fly.dev on the platform's injected port:

PORT=8080 \
KLARIDIAN_BIND_HOST=0.0.0.0 \
KLARIDIAN_ALLOWED_HOSTS=myapp.fly.dev \
npm start

Leaving KLARIDIAN_ALLOWED_HOSTS unset keeps the secure localhost-only default, so local runs need no configuration. Only the hostnames you list are accepted—an unlisted Host still gets a 403.

Which one should I pick?

Start with stdio. Switch to streamable-http only when you need remote access or OAuth.