MCP Dev Summit Seoul 2026

Same MCP server. Same prompt. Three different IDEs. Three different outcomes — and one of them is silently wrong.

After documenting a production MCP server across Cursor, Claude Desktop, and Windsurf, the speaker has the war stories. Tool descriptions one client truncates and another expands. Resource limits that vary by 10x. Notification semantics that work in one host and silently no-op in another. OAuth flows that route through different dances depending on the client. Session-lifetime assumptions that turn into "why did my context vanish?" support tickets.

This talk is a field guide, organized by client, with the actual diffs server authors should care about. Live side-by-side traces of the same tool call across three clients, showing where each one quietly diverges from the spec — and the small defensive changes (in tool naming, description length, error semantics) that make a single server work the same way in all three.

Closes with a proposal: a "client compatibility matrix" the MCP ecosystem should publish and maintain, modeled on Can I Use for the web.

For MCP server authors who have only ever tested in one client.