zekebuilds-lab/captcha-mcp

What it does

captcha-mcp is a Model Context Protocol (MCP) server middleware that implements L402 Lightning paywall functionality combined with Hashcash proof-of-work mechanisms. It provides two-tier access control for MCP tool calls: a free tier requiring users to solve computational proof-of-work challenges, and a premium tier accepting Lightning Network payments processed through self-hosted LNBits infrastructure.

How to set up

Clone the repository from GitHub and install dependencies. Configure your LNBits instance for Lightning payments (optional, for paid tier). Deploy the MCP server as middleware in front of your existing MCP tools. No API keys, user accounts, or third-party SaaS integration required—operates entirely on your infrastructure.

Key features

• Dual-tier access: Free PoW challenges or paid Lightning invoices
• L402 standard compliance for HTTP authentication
• Self-hosted payment processing via LNBits
• No user accounts or centralized authentication needed
• Works as drop-in middleware for any MCP server
• Supports multiple platforms: ChatGPT, Claude, AI Studio, Antigravity
• Privacy-preserving monetization model