21tunnel

21tunnel is an open-source tunneling service built for the age of AI coding agents. Assistants like Claude Code, Cursor, Aider, and Devin increasingly need public URLs for webhooks, previews, and MCP servers running on localhost — and the common workaround of pasting a full-access API token into the agent's environment creates serious security exposure. 21tunnel replaces it with a delegation pattern: a master key that cannot open tunnels itself mints scoped, short-lived child keys the agent works with, isolated per project, with one-click cascade revoke for everything the agent ever created.

Beyond the AI-agent workflow, it is a complete ngrok alternative: HTTP, TCP, SSH, and gRPC tunnels from a single static Rust binary, sticky subdomains, custom domains on the free tier, edge auth via Google sign-in, a live request inspector, and teams with RBAC plus audit logs. The entire stack self-hosts free forever under MIT and Apache-2.0.