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The Machine Payments Protocol (MPP) lets an HTTP client pay for a web service through a standardized request-and-response flow: the service issues a payment challenge, the client fulfills it and retries, and the service verifies the payment before returning the resource. Its three payment intents cover one-time charges, metered sessions and recurring subscriptions. MPP is a developing, payment-method-agnostic protocol—not a single coin, payment processor or finalized standard.
What is the Machine Payments Protocol?
MPP is an open protocol for machine-to-machine payments. It applies HTTP authentication semantics to payments so agents, applications and people can pay for a service through a common interface. Rather than assuming that a user can create an account, navigate a checkout page and type in payment details, MPP gives a client and server a way to negotiate and verify payment programmatically.
The design separates three concerns: the commercial intent (what kind of access is being purchased), the payment method (how value moves), and the HTTP transport (how the challenge, credential, receipt and any error are exchanged). The protocol is not itself a currency or a processor. Its specifications are published as Internet-Drafts, so implementations should be pinned to a documented version and checked against the current specifications as they evolve.
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Many web payment flows were designed around a person: create an account, choose a plan, enter payment information and configure billing. That is cumbersome when software needs to pay for a small amount of data, a model inference, an API request or one MCP tool call without stopping for a human checkout.
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Stripe introduced MPP with Tempo on March 18, 2026, describing it as an open standard for agents to pay programmatically, including microtransactions and recurring payments. Its stated use cases include browser sessions, physical mail ordered by an agent, food orders and programmatic contributions. These examples show the range of resources that can be sold through a machine-readable flow; they do not establish a general adoption rate for MPP.
How the HTTP payment flow works
- Request: The client requests a protected resource in the ordinary way.
- Challenge: If payment is required, the service responds with HTTP
402 Payment Requiredand a machine-readable payment challenge. - Fulfill: The client interprets the challenge and completes payment using an available method.
- Retry: The client sends the request again with a payment credential.
- Verify and respond: The service validates the credential and, if accepted, returns the resource with a payment receipt.
MPP uses WWW-Authenticate: Payment for the challenge, Authorization: Payment for the payment credential and Payment-Receipt for a successful receipt. Those fields make payment part of the HTTP exchange rather than a separate browser checkout. The service still has to decide whether the proof is valid and whether it authorizes the requested resource.
The same general exchange can be used with MCP tools through JSON-RPC. That lets an agent encounter a payment-required response while calling a tool and handle the challenge in the tool interaction rather than relying on a human to complete a conventional webpage checkout.
MPP’s three payment intents
An intent describes the commercial arrangement. It is distinct from the payment method used to transfer or authorize funds.
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| Intent | What it means | Typical use |
|---|---|---|
charge |
A one-time payment for a particular resource or action. | A paid data query, API call or browser session. |
session |
Measured usage, typically under a cap or deposit authorization. | An interaction whose final cost depends on how much of a service is consumed. |
subscription |
Recurring access or billing. | Ongoing access to a service rather than a single request. |
One-time charges
A charge is the simplest model: the client pays once for a defined transaction. Solana’s documentation describes two modes for a charge on Solana. In pull mode, the server verifies and broadcasts a signed transaction. In push mode, the client broadcasts the transaction and supplies its confirmed signature. The server’s implementation must verify what the transaction actually does; receiving a signature alone is not enough.
Metered sessions
A session is useful when the service is consumed over time or by usage units, so the final amount is not known at the first request. Solana’s documented session model uses an on-chain payment channel with a maximum deposit and cumulative signed vouchers. The server can check usage off-chain and settle the highest accepted amount later. This is a specific Solana implementation model, not a requirement that every MPP session use a payment channel.
Subscriptions
The subscription intent represents recurring access. The protocol’s separation of intent from payment method means the recurring arrangement can be expressed without making one particular asset or processor synonymous with MPP. Exact subscription behavior depends on the method and implementation; operators should consult the version of the specification and payment integration they actually deploy.
Which payment methods can MPP use?
MPP is designed to be payment-method agnostic. Cloudflare describes stablecoins, cards through Stripe and custom methods. Stripe describes support through its infrastructure for stablecoins as well as fiat card and buy-now-pay-later methods. Solana documents native SOL and SPL-token support for charges. These are documented paths in particular integrations, not a guarantee that every MPP server accepts every method.
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For a client, the practical question is what payment methods the service advertises in its challenge and what the client knows how to fulfill. For a service operator, support depends on the selected integration, assets, networks and verification or settlement components. Do not infer that a service accepts a particular token, card or network just because MPP itself is payment-method agnostic.
MPP vs. x402: what is different?
MPP and x402 both use HTTP 402 to make paid web resources available to software, and both can be used with stablecoins. They differ in their HTTP representation, payment models and settlement patterns. Neither is automatically the right choice for every service: the deciding factors are the intended billing model and the clients and infrastructure that need to interoperate.
| Area | MPP | x402 |
|---|---|---|
| Challenge | WWW-Authenticate: Payment |
PAYMENT-REQUIRED |
| Client authorization | Authorization: Payment |
PAYMENT-SIGNATURE |
| Receipt or response | Payment-Receipt |
PAYMENT-RESPONSE |
| Payment model | charge, session and subscription |
Schemes including exact, upto and batch settlement |
| Verification and settlement | Server validation, with optional relay or gateway | Local verification or a facilitator service |
| Fit described by Solana | HTTP authentication semantics and repeated metering | Pay-per-request resources and existing x402 clients |
Cloudflare says MPP clients can consume existing x402 services, so choosing MPP does not necessarily require abandoning those services. Solana’s comparison emphasizes choosing based on payment model and interoperability needs. Check the current implementations and supported schemes before treating the protocols as interchangeable: similarly named concepts do not mean their headers or credentials can be swapped.
What developers need to secure in production
A payment response is security-sensitive input. Solana’s production guidance calls for verifying the challenge and the resulting transaction or session state, not merely accepting a well-formed header.
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- Accepts all payment types: NFC/CTLS, mobile wallets, EMV and magstripe
- Supports a variety of third-party apps through Verifone’s Merchant Marketplace
- Optional features, such as dual-band WiFi and Bluetooth 4.2 BLE
- Supports Verifone’s estate management solution for remote device management, value-added services, updates and diagnostics
- Confirm the challenge is authentic, unexpired, bound to the request and intended for the correct realm.
- For transactions, verify the expected network, asset, recipient, amount and token program.
- Confirm the transaction succeeded at the required commitment level before granting access.
- Prevent replay: ensure a payment signature has not already been consumed, and make replay checking and consumption atomic across server instances.
- For sessions, persist channel state, the accepted cumulative amount and the settlement watermark.
- Document how unused funds are recovered if the server becomes unavailable.
These checks address different failure modes. Challenge binding limits using a valid payment proof for the wrong request; expiry limits stale proofs; transaction checks catch a transfer to the wrong recipient or for the wrong amount; and atomic replay protection prevents concurrent server instances from granting access twice for one payment. Durable session state is essential if a service must resume safely after a restart.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Implementation choices and versioning
Cloudflare documents charging a Worker route or MCP tool and using its Agents SDK to pay HTTP services. Solana provides an Express example using @solana/pay-kit, @solana/kit and an MPP-enabled route. Its example’s sandbox defaults are not production settings: operators must explicitly configure the network, recipient, RPC endpoint, signer and replay storage.
Before implementing, decide which intent you need, which payment method and network you will accept, where verification happens, and what state must persist. Then pin the MPP specification and SDK versions used by the service and client. The specifications remain Internet-Drafts; Solana identifies the current specifications at paymentauth.org as the source of truth, and the MPP site lists 2026 updates covering identity support, relays, sessions and EVM/x402 support. A draft or integration update can change details, so recheck the current specification rather than relying on an older example as a permanent contract.
Where ScreenshotNeo fits—and where it does not
ScreenshotNeo is a website screenshot API and MCP server, not an MPP payment method, payment processor or documented MPP integration. If an agent needs a screenshot resource, it can use ScreenshotNeo as the screenshot service; whether an MPP-enabled intermediary charges for access to any resource is a separate service design. ScreenshotNeo’s endpoint uses an access key, so do not treat that key as an MPP payment credential.
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- Accepts all payment types: NFC/CTLS, mobile wallets, EMV and magstripe
- Supports a variety of third-party apps through Verifone’s Merchant Marketplace
- Optional features, such as dual-band WiFi and Bluetooth 4.2 BLE
- Supports Verifone’s estate management solution for remote device management, value-added services, updates and diagnostics
For developers building an agent workflow that needs a screenshot, ScreenshotNeo is an alternative to building and operating a browser-capture stack: it returns a screenshot or PDF from one GET request. It can accept cookie or consent banners and remove more than 60 known consent platforms, newsletter popups and chat widgets before capture; those steps can be disabled. Bot checks, blank pages, timeouts, failed loads and cache hits are not billed, and response headers indicate the page verdict and billing status. Its MCP server provides take_screenshot, get_page_info and capture_pdf for AI agents.
For example, this cURL request captures a page as WebP:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpSee the ScreenshotNeo API documentation for request options. The free plan includes 1,000 screenshots per month with no card; paid plans start at $5 for 3,000. Learn about ScreenshotNeo or sign up for 1,000 free screenshots a month, with no card.
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Frequently Asked Questions
Does using HTTP 402 mean the client has already paid?
No. A 402 response is the service’s payment challenge; the client still has to fulfill it and retry with a credential that the service verifies.
Does MPP require cryptocurrency?
No. MPP separates the payment flow from the payment method. Particular implementations may support stablecoins, cards, SOL, SPL tokens or custom methods, but support depends on the service.
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