Inspect, debug, and test Machine Payments Protocol (HTTP 402) endpoints directly from Claude Code. Parses spec-compliant WWW-Authenticate challenges, discovers MPP endpoints on any domain, compares pricing across services, validates receipts, and dry-runs payment flows. Supports Tempo, Stripe, Lightning, Solana, and Card payment methods. Includes 4 slash commands (/mpp-inspect, /mpp-scan, /mpp-flow, /mpp-protocol) and 5 MCP tools for programmatic access.