Beyond parameter types, you might need to provide additional type information about state or context properties that aren't covered by the global declarations in core/api/env.d.ts.

Perhaps a specific route uses middleware that adds context properties that aren't used elsewhere, making them inappropriate for the global interface.

The defineRoute function is a generic that accepts three type arguments, all optional.

🔹 The first is a params refinement tuple we just covered.

🔹 The second lets you type the ctx.state object.

🔹 The third lets you declare additional properties on the context object.

api/example/index.ts

import { defineRoute } from "@front/{api}/users/[id]";
import type { User } from "@front/types";

export default defineRoute<
  [number], // params refinements
  { permissions: Array<"read" | "write"> }, // route-specific state
  { authorizedUser: User }, // route-specific context
>(({ GET }) => [
  GET(async (ctx) => {
    // ctx.typedParams.id is number
    // ctx.state.permissions is Array<"read" | "write">
    // ctx.authorizedUser is User
  }),
]);

This approach is useful for route-specific types, but remember that if you find yourself declaring the same context properties in many routes, it's better to add them to DefaultContext in core/api/env.d.ts instead. (Details)

Use route-specific type arguments for properties that truly are unique to specific endpoints.