Rank 6previewMPP

Machine Payments Protocol (MPP)

The 'Payment' HTTP authentication scheme — one 402 challenge, many payment methods

preview: The core is draft-ryan-httpauth-payment-01 (March 2026), an individual Internet-Draft with no formal IETF standing; method and intent specs are also drafts.

Vendor documentation Website

Rank: 6 of 14
Composite score: 8.3 / 10
Schemes: MPP
Role: Pays 402 challenges; Charges with 402
Kind: protocol
Maturity: preview
Protocol / rail: Multi-method: Tempo, Stripe, Lightning, EVM, Solana and more
Assets: USD (card), USDC, BTC (Lightning), other stablecoins
Networks: tempo, solana, evm, lightning, stellar, xrpl, hedera, card
Custody model: Depends on the payment method (self-custodial methods exist)
Node management: Not required
MCP native: No
License: Not stated
Last verified: 2026-10-15

Overview

The Machine Payments Protocol, co-authored by Tempo and Stripe and launched in March 2026, defines a 'Payment' HTTP authentication scheme. A server answers with 402 and WWW-Authenticate: Payment carrying an id, realm, method, intent and a base64url-encoded JSON request; the client pays through the named method and retries with Authorization: Payment and a base64url credential; successful responses may carry a Payment-Receipt. The core is method-agnostic, with drafts for charge, session and subscription intents and for methods including Tempo, Stripe, card, Lightning, EVM, Solana, Stellar and others, plus drafts for discovery and an MCP transport. Stripe and Lightning Labs' Aperture implement it server-side. It is still a draft: the core is an individual Internet-Draft with no formal IETF standing, and custody, fees and speed depend on the method.

Key advantages

Method-agnostic: one challenge format across cards, stablecoins and Lightning
Standard HTTP authentication framing — WWW-Authenticate and Authorization: Payment, with a Payment-Receipt
Charge, session and subscription intents
Drafts for discovery and for an MCP / JSON-RPC transport
Implemented server-side by Stripe and by Lightning Labs' Aperture

Trade-offs

An individual Internet-Draft with no formal IETF standing; method specs are still drafts
Custody, fees and settlement speed depend entirely on the method chosen
A younger ecosystem than x402

Evaluation matrix

Custody & Sovereignty8.0
Self-custodial with exit guarantees vs. centralized/custodial risk. A 10 means the holder keeps their own keys and can unilaterally exit to the base chain; a custodial platform scores around 4.
Operational Friction8.0
Infrastructure burden. Zero nodes, channels or liquidity to manage scores a 10; running and maintaining your own Lightning node scores around 4–5.
Agent Native Support8.5
Out-of-the-box MCP server integration, typed tool calls and LLM-friendly setup. A first-party MCP server scores 9–10; a library or CLI an agent can drive scores 6–8.
Payment Rails & Assets9.5
Breadth of settlement rails and assets: Lightning for true micropayments, stablecoins for a stable unit of account, cards for mainstream reach. A single asset on a single network scores around 7.
Settlement Speed & Fees8.0
Instant sub-second settlement with near-zero overhead scores a 10. Block-bound settlement scores around 8; card-network settlement and fees score lower.
Developer DX7.5
SDK quality, documentation, maintenance and copy-paste integration speed. Alpha-stage API churn, stale releases or inconsistent docs lower the score.

Why these scores. Custody 8: self-custodial methods exist, but it depends on the method. Friction 8: the protocol needs no node; method infrastructure varies. Agent 8.5: an MCP transport is drafted in the spec. Rails 9.5: the broadest method coverage of any scheme. Settlement 8: method-dependent. DX 7.5: draft specs and a 0.x SDK.

Integration

TypeScript SDK

npm install mppx

Challenge — example from the IETF draft

HTTP/1.1 402 Payment Required
Cache-Control: no-store
WWW-Authenticate: Payment id="x7Tg2pLqR9mKvNwY3hBcZa",
    realm="api.example.com",
    method="example",
    intent="charge",
    expires="2025-01-15T12:05:00Z",
    request="eyJhbW91bnQiOiIxMDAwIiwiY3VycmVuY3kiOiJVU0QiLCJyZWNpcGllbnQiOiJhY2N0XzEyMyJ9"

Best for

Services that want one 402 integration accepting several payment methods — cards, stablecoins and Lightning.

Sources

Every claim on this page was checked against these sources on 2026-10-15. Maturity “preview” means: the vendor labels it preview, frontier, or draft.

Machine-readable

fetch this entry as JSON

curl "https://402mcp.org/api/v1/solutions?id=machine-payments-protocol&view=full"

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