Machine Payments Protocol (MPP)

The open protocol for machine-to-machine payments.

• IETF Draft: the core specification
• Full Rendered Spec: all specs including methods and extensions
• Learn more

What is MPP?

The Machine Payments Protocol (MPP) is an open standard for machine-to-machine payments, co-authored by Tempo and Stripe. Paying for an internet resource, such as an API call, a dataset, or a unit of compute, still typically requires an account, API key, or billing relationship set up in advance. MPP lets any client pay as part of the HTTP exchange using the native 402 Payment Required status code.

Primary use cases include agentic payments, such as an AI agent paying per API call, machine-to-machine commerce, and usage-based billing without pre-provisioned accounts.

MPP lets businesses offer services to agents, apps, and humans via a standard HTTP control flow. The protocol defines a payment-method agnostic core alongside extensions for specific payment method flows, discovery, and identity.

sequenceDiagram
    participant Client
    participant Server

    Client->>Server: GET /resource
    Server-->>Client: 402 Payment Required<br/>WWW-Authenticate: Payment ...

    Note over Client: Client fulfills payment challenge

    Client->>Server: GET /resource<br/>Authorization: Payment credential
    Server-->>Client: 200 OK

1. Client requests a protected resource
2. Server responds with 402 Payment Required and a WWW-Authenticate: Payment challenge describing what payment is needed
3. Client fulfills the payment (off-band, via the specified payment method)
4. Client retries the request with an Authorization: Payment credential proving payment
5. Server validates the credential and grants access

Design Principles

MPP is designed to be simple, secure, and performant, holding the following design principles as guides:

• Extensible core: Minimal protocol designed for safe extension.
• Network agnostic and multi-rail: Designed to support a number of payment networks and settlement layers, including bank rails, credit cards, and stablecoins.
• Currency agnostic: No implicit advantages for any currency or asset.
• Durable by design: All designs follow web standards and are designed for security and replay protection as first class concerns.

See STYLE.md for the full design principles and RFC writing conventions.

Architecture

The specification is modular, separating stable protocol mechanics from evolving payment ecosystems:

• Core: HTTP 402 semantics, headers, IANA registries.
• Intents: Abstract payment patterns such as charge, authorize, and subscription. Define what kind of payment without specifying how.
• Methods: Concrete implementations for specific networks (Tempo, Stripe, ACH).
• Extensions: Optional protocol additions, such as discovery and identity.

Related projects

The MPP repository contains the mpp.dev documentation and service directory. SDKs are available for TypeScript, Python, Rust, Go, and Ruby.

Contributing

The Machine Payments Protocol specification is currently maintained by the following organizations:

• Tempo Labs
• Stripe

We welcome contributions from a wide variety of individuals and organizations.

See CONTRIBUTING.md for building instructions and contribution guidelines.

License

Specifications: CC0 1.0 Universal (Public Domain)

Tooling: Apache 2.0 or MIT, at your option