A new macOS terminal app called Calyx ships with a built-in MCP server that lets Claude Code and Codex CLI instances running in separate panes discover each other and exchange messages — no custom integration required. Activate it from the command palette and Calyx writes the necessary config entries to ~/.claude.json and ~/.codex/config.toml automatically. The exposed tools — register_peer, list_peers, send_message, broadcast, receive_messages, ack_messages, and get_peer_status — give agents a direct coordination channel across panes and tabs.
A separate set of 19 <a href="/news/2026-03-14-agent-browser-protocol-abp-chromium-fork-ai-agent-web-navigation">browser automation MCP tools</a> rounds out the agent story. Those let agents control an embedded WKWebView, snapshot accessibility trees, interact with page elements, and execute JavaScript — all from within the terminal environment.
Calyx is built by developer yuuichieguchi on top of libghostty, the embeddable rendering engine that powers Mitchell Hashimoto's Ghostty terminal. The stated motivation was simple: Ghostty lacks tab organization, so yuuichieguchi built the wrapper to fill that gap. On top of Ghostty's Metal GPU-accelerated renderer, Calyx layers tab groups with color coding, split panes, session persistence, a command palette, inline git diff view, and a WKWebView browser panel. It targets macOS 26 (Tahoe) and is built with Swift 6.2, AppKit, and SwiftUI.
The Hacker News thread surfaced some caveats worth reading. Commenter jasonjmcghee questioned whether the advertised Liquid Glass UI is genuine — Apple's SwiftUI Liquid Glass API takes only a few lines, and jasonjmcghee suggested the codebase may not actually use it. The same commenter flagged discrepancies between comments claiming features are implemented and their apparent absence in the code. The MCP server architecture appears to be the most fully realized piece; the macOS Tahoe design language angle looks more aspirational at this stage.
Calyx is available via Homebrew or manual download.