Agents, Browser Run - Agents SDK: Preview dev servers in the browser without public URLs
Cloudflare Agents SDK introduces internal hostnames, allowing an agent's browser to securely preview internal dev servers or sandboxes without exposing them to the public internet.
Why this signal matters
Cloudflare Agents SDK (v0.31.0 and later) now supports internal hostnames in its persistent browser environment. This feature enables agents that build websites or applications to navigate and preview sandboxed dev servers, local workspace folders, or companion Workers without publicly exposing those services. Requests to specified internal hostnames (such as preview.internal) are routed to a fetch function executing inside the agent's Durable Object, retaining access to the object's bindings and state, or directly to another Worker via service bindings. Target schemas can be configured so models dynamically determine target parameters such as ports or directories. The capability works independently of specific harnesses, offering built-in adapters for Pi Durable, AI SDK, and TanStack AI, as well as a generic implementation via browser.session().
Actionable summary
Cloudflare Agents SDK v0.31.0+ adds internal hostnames to its persistent browser feature, routing requests (e.g., preview.internal) to a Durable Object fetch handler or service binding instead of the public web.
- Agent usefulness
- 80/100
- Confidence
- 90%
- Canonical data
- JSON + Markdown
What builders should check
- Upgrade to Cloudflare Agents SDK version 0.31.0 or higher if internal browser dev server previewing is needed.
- Configure internalHosts in the browser configuration and define fetchInternalHost() or corresponding fetch logic in the Durable Object to route private requests.