Navigation: instant without a client router

The feature

June ships no client router — and navigation is still instant, because the browser already has one. Every HTML page carries three things:

  1. Speculation Rules. A <script type="speculationrules"> block tells the browser to prerender same-origin links on hover (eagerness: moderate). By the time you click, the next page is already rendered — the click is a zero-network activation.
  2. A fallback for the rest. Browsers without Speculation Rules get a tiny inline script that turns pointerover into <link rel="prefetch"> — progressive enhancement, not a polyfill bundle.
  3. View Transitions. @view-transition { navigation: auto } animates the document swap (and respects prefers-reduced-motion). Cross-document navigation stops looking like a full reload because the browser paints it as one continuous surface.

The agent surfaces are deliberately excluded: .md, .json, and /mcp never prerender — machines don't hover.

Try it right now

This page is the demo. Hover any link in the sidebar, watch the network panel prerender it, then click: no fetch, one smooth transition. Everything you just experienced shipped as ~1KB of declarative rules — not a router, not a virtual DOM, not a client cache to invalidate.

The posture

Client routers exist to make navigation fast and transitions smooth. The platform now does both natively, so June's default is the same choice it makes everywhere (Standards): use the browser's mechanism and ship nothing. This is also why a full document — not a Flight payload (RSC) — is what crosses the wire: it covers most sites with zero client state to manage.

When an app-like surface genuinely needs in-memory state to survive a navigation (a dashboard, an open websocket), the opt-in Client Router adds soft swaps as progressive enhancement — off by default, and this site keeps it off.

Configured by speculation in june.config.ts, on by default — the config exists to turn it off.

Why it matters

A client router is the single biggest source of accidental JavaScript: the router pulls in state, the state pulls in hydration, and suddenly a document site ships a runtime. Letting the browser navigate keeps the zero-JS default (Islands) honest.