Claude Simulator for MCP Apps: Test Claude Apps Locally with sunpeak

TL;DR: sunpeak v0.15 adds a local Claude simulator. Run sunpeak dev , pick Claude from the Host dropdown (or ?host=claude URL Param), and test your MCP App in both Claude and ChatGPT from one dev server. Until now, sunpeak's local simulator only replicated the ChatGPT runtime. If you wanted to test how your MCP App looked in Claude, you had to deploy it and connect it manually. That's fixed. sunpeak v0.15 ships with first-class Claude support. The old ChatGPTSimulator is now just Simulator , and both Claude and ChatGPT are registered as host shells out of the box. Switch between them with a dropdown, a URL param, or a prop. What Changed The simulator is now multi-host. Instead of a single ChatGPT-specific component, sunpeak uses a pluggable host shell system. Each host registers its own conversation chrome, color palette, and theme behavior. The Simulator component renders whichever host you select. Two hosts ship by default: ChatGPT uses the familiar gray/white palette with the ChatGP