sunpeak
Open-source MCP framework for cross-platform AI apps and testing
The only open-source framework purpose-built for cross-platform MCP app development. Strong testing tooling and local inspector make it invaluable for serious developers, but steep learning curve limits appeal for non-React teams.
- Developers building ChatGPT Apps with React
- Developers building Claude Connectors with custom UI
- Teams needing to test MCP servers in CI/CD without accounts
- Prototyping interactive chat-based AI apps for multiple hosts
- Non-developers looking for a no-code chat builder
- Organizations that require a hosted platform with SLAs
- Teams using non-React frontend frameworks
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In short
sunpeak — Open-source MCP framework for cross-platform AI apps and testing. Best for Developers building ChatGPT Apps with React, Developers building Claude Connectors with custom UI, Teams needing to test MCP servers in CI/CD without accounts. Free to use.
What's new in sunpeak
Checked 14 days agoAcross the latest 7 updates: 7 feature updates.
Live Testing for Claude Connectors and ChatGPT Apps: Test Against Real Hosts with Playwright
Sunpeak introduces Playwright-based live testing against real ChatGPT and Claude sessions for end-to-end validation.
Debugging Claude Connectors: Fix Common Errors in Development and Production
Guide to diagnosing and fixing connection failures, OAuth errors, and UI rendering bugs in Claude Connectors.
Claude Connector Authentication: How OAuth Works and When You Need It
Developer guide to OAuth 2.1 for Claude Connectors including callback URLs and submission requirements.
What Are Claude Connectors? Data Access, Auth, Custom Setup, and Troubleshooting
Overview of Claude Connectors: data access via MCP, authentication, and troubleshooting common issues.
The Fastest Way to Prototype ChatGPT & MCP Apps
Guest post on validating ChatGPT App ideas with users before committing engineering time.
Claude Connectors Tutorial: Build and Deploy a Connector to Claude
Step-by-step tutorial building an interactive Claude Connector from scratch with ngrok and directory submission.
Claude Inspector for MCP Apps: Test Claude Connectors Locally with sunpeak
New Inspector tool allows local testing of Claude Connectors and MCP Apps with multi-host runtime switching.
What independent users actually report about sunpeak
We ran a structured research pass across product reviews, community discussions, and post-purchase forum threads to surface the patterns vendors won't publish themselves. Below: the recurring strengths, the hidden costs people mention most, and the cohort that consistently regrets adopting this tool.
49 mentions across 4 sources (Hacker News, YouTube, Bluesky, GitHub).
- +Eliminates platform boilerplate for building MCP apps across ChatGPT and Claude.
- +Multi-host inspector replicates ChatGPT and Claude runtimes for local testing.
- +Hot-reloading dev server speeds up development iteration cycles.
- +Built-in Playwright E2E testing with visual regression across hosts.
- +Simulation fixtures enable testing without needing real host accounts.
- −Very early-stage with few GitHub stars and scarce community feedback.
- −OAuth authentication for secrets under construction.
- −URL state not persisted in inspector, hampering reproducibility.
- −Documentation limited mainly to tutorials and blog posts.
- −Name confusion with Sun Peaks ski resort dominates search results.
Viability Score
How likely is sunpeak to still be operational in 12 months? Based on 4 signals — momentum (how recently it shipped), wrapper dependency, revenue model, and web presence.
Last calculated: July 2026
How we score →Key Features
- Convention-over-configuration MCP app framework
- Multi-host inspector (ChatGPT & Claude runtimes)
- 20+ typed React hooks for cross-platform development
- Hot-reloading MCP dev server
- Built-in Playwright E2E testing
- Visual regression testing across hosts and themes
- Live host tests against real ChatGPT and Claude sessions
- Multi-model tool calling evaluations
- Simulation fixtures for testing without accounts
- CLI for scaffolding, building, testing, and shipping
- Auto-discovery of tools, resources, and simulations
- Pre-built MCP App UI components following host guidelines
- ChatGPT App and Claude Connector support from one codebase
- CI/CD integration with no paid accounts needed
- OAuth 2.1 flow for Claude Connector authentication
About sunpeak
sunpeak is an open-source (MIT), server-agnostic MCP testing framework and full-stack MCP App framework. It lets you build interactive UIs that run inside AI hosts like ChatGPT and Claude via the Model Context Protocol. With sunpeak, you can create ChatGPT Apps and Claude Connectors from a single codebase without needing paid host accounts or AI credits. The framework provides a convention-over-configuration project structure where tools, resources, and simulations are auto-discovered from the filesystem. It includes a dev server with hot reloading, a multi-host inspector for testing in replicated ChatGPT and Claude runtimes, and 20+ typed React hooks for cross-platform development. sunpeak also features a built-in testing framework with Playwright E2E tests, visual regression testing, live host tests, and multi-model evals. What makes sunpeak different is its focus on cross-platform compatibility and developer tooling. Unlike rolling your own MCP setup, sunpeak abstracts away protocol message routing, resource HTML bundling, and platform-specific CSS variables. You write your app once and deploy it to ChatGPT, Claude, and future MCP-compatible hosts. The testing framework works with any MCP server (Python, Go, TypeScript, Rust, etc.) and replicates host environments for CI/CD testing without needing accounts or API credits. sunpeak is ideal for developers building chat-based applications for AI assistants, especially those targeting multiple platforms. It reduces boilerplate, provides a consistent development and testing experience, and is well-documented with a growing library of tutorials and blog posts.
Behind the Verdict
sunpeak fills a real gap for developers building MCP apps that need to run inside both ChatGPT and Claude. The convention-over-configuration approach cuts boilerplate significantly compared to wiring up an MCP server from scratch. The multi-host inspector is a standout feature — you can toggle between ChatGPT and Claude runtimes locally, see how your UI renders with host-specific themes, and test without needing paid accounts. The testing framework is where sunpeak really shines. Playwright E2E tests, visual regression across hosts/themes, live tests against real ChatGPT/Claude sessions, and multi-model evals cover CI/CD needs comprehensively. The recent live testing capabilities (announced June 2026) make it even more robust for production workflows. When should you pick sunpeak? If you're a React developer building ChatGPT Apps or Claude Connectors and want to maintain a single codebase, it's likely the best option. The CLI tooling (npx sunpeak new) gets you started fast with discoverable project structure. When should you pass? If your team isn't using React, sunpeak's pre-built hooks and components won't help. Non-developers looking for no-code chat builders should look elsewhere — this is squarely a developer tool. Also, if you only need a lightweight MCP server without any UI, a minimal npm package might be simpler. Compared to rolling your own MCP setup, sunpeak saves time on protocol routing, hot reloading, and testing infrastructure. The tradeoff is learning its conventions and React dependency. For teams already invested in React and targeting multiple MCP hosts, the investment pays off quickly.
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Use Cases
- Build a customer support chat widget that works in both ChatGPT and Claude.
- Test an MCP server’s response quality with automated multi-model evals.
- Prototype a data visualization tool that renders as an interactive resource inside Claude.
- Create a Claude Connector that accesses a live database and returns formatted results.
- Run Playwright tests against simulated ChatGPT runtime to catch UI regressions before deployment.
Limitations
- Requires familiarity with MCP protocol, React, and Node.js.
- Testing features are primarily CLI-based; no graphical test runner UI is provided.
- The framework is still relatively new, so community and third-party integrations are limited compared to established web frameworks.
Integrations
Resources & Guides
Official links
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