Define your API once in plain TypeScript. Get end-to-end inference, one proxy route for every endpoint, React Query bindings and middleware — against any REST backend, which needs zero changes.
WORKS WHERE YOU ALREADY ARE
Ten official server adapters, each one line to mount — and any client that can call fetch.
SCROLL TO REFACTOR
SCROLL TO REFACTOR
Keep scrolling. This is what one typed, proxied, cache-aware call costs today — and what is left once Courier owns it.
3 files · 20 lines left
Each one is shown running below. All of it ships with Courier — nothing to find, nothing to wire by hand.
UPLOADS
In the browser it comes from XHR: onUploadProgress reports percent and bytes as they leave the machine — not a jump from 0 to 100.
await caller.files .with({ onUploadProgress: (p) => setPct(p.percent * 100) }) .upload(form)
STREAMING
One option turns the response into a stream. SSE and chunked bodies paint token by token.
const body = await caller.chat .with({ stream: true }) .ask({ q })
DEDUPLICATION
Three components ask for the same user. One derived query key, one request.
// the same read in three components q.users.useQuery("getById", { variables: { id: "5" }, })
MIDDLEWARE
Koa-style middleware wraps every call in both directions — logging, retry, auth, rate limits and caching compose in the order you list them.
middleware: [ logMiddleware(), retryMiddleware({ limit: 3 }), authMiddleware({ getToken }), ]
VALIDATION
Pass a Zod, Valibot or ArkType schema to .variables(). Types are inferred from it and invalid data is stopped before the network.
create: endpoint.post("") .variables(CreateUser) .response(UserSchema)
catch (error)unknownisHTTPError<ApiError>(error)trueerror.status404error.data.message"User not found"ERRORS
Every non-2xx rejects with an HTTPError carrying status, headers and a typed body. The guard narrows unknown in a single line.
if (isHTTPError<ApiError>(error) && error.status === 404) notFound()
Not a handler per endpoint — a single zero-argument handler that reads your registered sources and does the tedious parts for you.
// app/api/request/route.ts import { apiRoute } from "@noverax/courier-next" export const { GET, POST } = apiRoute()
Your backend can be Express, FastAPI, Rails, Go or Laravel. Courier asks nothing of it — unlike tRPC, which requires the server to be yours.
MCP SERVER
Mark an endpoint .agent() and Claude Code, Cursor or any MCP client can call it — typed from your schemas, run through your middleware, and recorded in Studio.
cancel: endpoint .post(":id/cancel") .variables(z.object({ id: z.string() })) .agent({ description: "Cancel an order that has not shipped yet", access: "destructive", })
cwd ~/shop · MCP shop (courier-mcp) connected, 2 tools
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STUDIO · TIMELINE
Full inference like tRPC — but against a REST backend you do not control.
| FEATURE | fetch2 / 12 | axios3 / 12 | tRPC7 / 12 | courier12 / 12 |
|---|---|---|---|---|
| Type safety | Manual casts | Manual casts | Full | Full inference |
| Any REST backend | Yes | Yes | tRPC server only | Unchanged |
| No code generation | None | None | None | None |
| React Query | Manual | Manual | Built-in | Built-in |
| Server components | Manual | Manual | Server callers | First-class |
| Middleware | No | Interceptors | Built-in | Koa-style chain |
| Runtime validation | No | No | Any validator | Any Standard Schema |
| Upload progress | No | Yes | No | Built-in |
| Typed streams & sockets | Manual | No | Subscriptions | SSE and WebSocket |
| Retries & caching | Manual | Plugins | Via React Query | Built-in |
| Mock server from the API | Separate tool | Separate tool | Separate tool | From the definition |
| Devtools for every call | Browser only | Browser only | Community tools | Courier Studio |
Every adapter handler is zero-argument — it reads sources from the registry. Switch frameworks: only the import and one call change.