machine-payments-protocol

Machine Payments Protocol (MPP)

• Name: Machine Payments Protocol (MPP)
• URL: https://mpp.dev/
• Category: machine-payments protocol / HTTP 402 payment standard / multi-rail paid-request infrastructure
• Tags: bitcoin-ecosystem ethereum-ecosystem
• Summary: MPP is a general paid-request auth spec, not a rail. It defines a WWW-Authenticate: Payment / Authorization: Payment pattern and lets concrete methods plug in cards, stablecoins, Lightning, and other networks. The useful part is the abstraction layer: one grammar, many settlement methods.
• What it does:
  • Standardizes a machine-payment flow where servers return 402 Payment Required plus a WWW-Authenticate: Payment challenge and clients retry with an Authorization: Payment credential
  • Defines reusable protocol objects such as challenges, credentials, receipts, payment intents, and method identifiers
  • Publishes SDK and transport guidance for ordinary HTTP APIs as well as MCP and other machine-oriented service patterns
  • Supports multiple payment methods rather than binding the protocol to one rail
  • Frames itself as infrastructure for paid APIs, AI tool calls, and machine-to-machine commerce
• Key claims:
  • The official site calls MPP the open standard for machine-to-machine payments via HTTP 402
  • The docs and public draft say the core protocol is payment-method agnostic and designed to work across different networks and currencies
  • The architecture separates core mechanics from method-specific payment specs, which is the main reason to track MPP as a protocol layer instead of as a Stripe or Tempo feature
  • The docs explicitly market MPP for paid APIs, AI tool calls, MCP servers, and micropayments rather than human checkout alone
  • The protocol is trying to normalize paid-request semantics above whichever concrete rail does the money movement
• Whitepaper: No canonical standalone MPP whitepaper or litepaper surfaced in this pass. The clearest current source of truth is the official MPP docs site, the public mpp-specs repository, and the linked IETF Internet-Draft for the Payment HTTP authentication scheme; see ../../whitepapers/machine-payments-protocol-primary-sources-2026-05-02.md.
• Sources:
  • https://mpp.dev/
  • https://mpp.dev/protocol/
  • https://mpp.dev/payment-methods/
  • https://raw.githubusercontent.com/tempoxyz/mpp-specs/main/README.md
  • https://datatracker.ietf.org/doc/draft-ryan-httpauth-payment/

Internal linkages

• Closest protocol peers: x402 and l402

• Main contrast when discovery or grants matter more than request auth: open-payments

• Last reviewed: 2026-05-30 UTC