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The Subtext hosted browser runs in the cloud — which means it can’t reach your localhost dev server directly. The tunnel solves this: a separate local MCP server (subtext-tunnel) runs on your machine, bridges the hosted browser to your local server, and hands your agent a relay URL it can pass to live-connect.
Tunnel is part of the Verify beta. It is available to the closed beta cohort and may change before general availability.

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How the tunnel works

When you start a tunnel, subtext-tunnel opens a reverse connection from your machine to Subtext’s relay infrastructure. The hosted browser then reaches your local dev server through that relay — no firewall changes, no public IP required. Your agent calls tunnel-connect from the local side and live-tunnel from the hosted browser side to get the relay URL.
subtext-tunnel is a separate MCP server from the main Subtext MCP. It runs entirely on your local machine. Add it as a second entry in your MCP config — do not replace your existing Subtext entry with it.

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Add subtext-tunnel to your MCP config

Add the following entry alongside your existing Subtext MCP server configuration:
Your MCP config will have two entries when both are present: one for the main subtext server and one for subtext-tunnel.

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Tunnel tools

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Connect your agent to localhost

1

Add subtext-tunnel to your MCP config

Add the subtext-tunnel entry shown above to your MCP configuration file. Restart your agent or MCP host to pick up the new server.
2

Start your local dev server

Run your development server as usual — for example, npm run dev on port 3000. Confirm it is reachable at http://localhost:3000 before proceeding.
3

Open a tunnel from the local side

Ask your agent to call tunnel-connect with your local server URL:
This establishes the reverse connection from your machine to the relay.
4

Get the relay URL on the hosted browser side

Ask your agent to call live-tunnel on the hosted browser side. It returns the relay URL that the cloud browser can reach.
5

Open your app in the hosted browser

Pass the relay URL to live-connect. The hosted browser navigates to your local app through the tunnel, and your agent can interact with it just like any other live session.