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Overview

fx is Vercel Labs’ native CLI coding agent — a minimalist, terminal-first agent with a small built-in tool surface and first-class MCP support. Instead of loading every connected server’s full tool list up front, fx searches for the right capability on demand and only pulls in the tool it needs, which keeps context usage low even with several MCP servers connected. Connecting Kernel’s MCP server gives fx a real cloud browser: it can create a session, drive it with Playwright via execute_playwright_code, and tear it down — the same toolset described in the MCP server reference, including managed auth, profiles, proxies, and replays.

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Setup

Follow the fx client guide to add Kernel to ~/.fx/mcp.json. Two paths, depending on how you run fx:
  • Interactive session (recommended) — kernel mcp install --target fx, then /mcp reload and /mcp auth kernel --open to authorize via OAuth in a browser.
  • Headless or scripted (fx ask, fx acp, CI) — OAuth needs a browser, so it doesn’t work outside an interactive session. Use a Kernel API key with bearer_token_env instead; see Headless and scripted use for the config.

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Example

With Kernel connected, fx can drive a browser from a single prompt:
fx searches its connected servers for the right capability, calls manage_browsers to create the session, execute_playwright_code to read the title, and manage_browsers again to delete it:

fx MCP client guide

Full setup steps, including headless auth

MCP Server

All tools the Kernel MCP server exposes

execute_playwright_code

Run Playwright against a session