"1 line of code to accept digital dollars. No fee, 2 second settlement, $0.001 minimum payment."
app.use(
// How much you want to charge, and where you want the funds to land
paymentMiddleware("0xYourAddress", {"/your-endpoint": "$0.01"})
);
// Thats it! See examples/typescript/servers/express.ts for a complete example. Instruction below for running on base-sepolia.Payments on the internet are fundamentally flawed. Credit Cards are high friction, hard to accept, have minimum payments that are far too high, and don't fit into the programmatic nature of the internet. It's time for an open, internet-native form of payments. A payment rail that doesn't have high minimums + % based fee. Payments that are amazing for humans and AI agents.
- Open standard: the x402 protocol will never force reliance on a single party
- HTTP Native: x402 is meant to seemlessly compliment the existing HTTP request made by traditional web services, it should not mandate additional requests outside the scope of a typical client / server flow.
- Chain and token agnostic: we welcome contributions that add support for new chains, signing standards, or schemes, so long as they meet our acceptance criteria layed out in CONTRIBUTING.md
- Trust minimizing: all payment schemes must not allow for the facilitator or resource server to move funds, other than in accordance with client intentions
- Easy to use: x402 needs to be 10x better than existing pays to pay on the internet. This means abstracting as many details of crypto as possible away from the client and resource server, and into the facilitator. This means the client/server should not need to think about gas, rpc, etc.
Roadmap: see ROADMAP.md
resource: Something on the internet. This could be a webpage, file server, RPC service, API, any resource on the internet that accepts HTTP / HTTPS requests.client: An entity wanting to pay for a resource.facilitator server: A server that facilitates verification and execution of on-chain payments.resource server: An HTTP server that provides an API or other resource for a client.
- Permissionless and secure for clients and servers
- Gassless for client and resource servers
- Minimal integration for the resource server and client (1 line for the server, 1 function for the client)
- Ability to trade off speed of response for guarantee of payment
- Extensible to different payment flows and chains
The x402 protocol is a chain agnostic standard for payments on top of HTTP, leverage the existing 402 Payment Required HTTP status code to indicate that a payment is required for access to the resource.
It specifies:
- A schema for how servers can respond to clients to facilitate payment for a resource (
PaymentRequirements) - A standard header
X-PAYMENTthat is set by clients paying for resources - A standard schema and encoding method for data in the
X-PAYMENTheader - A recommended flow for how payments should be verified and settled by a resource server
- A REST specification for how a resource server can perform verification and settlement against a remote 3rd party server (
facilitator) - A specification for a
X-PAYMENT-RESPONSEheader that can be used by resource servers to communicate blockchain transactions details to the client in their HTTP response
The following outlines the flow of a payment using the x402 protocol. Note that steps (1) and (2) are optional if the client already knows
the payment details accepted for a resource.
-
Clientmakes an HTTP request to aresource server -
Resource serverresponds with a402 Payment Requiredstatus and aPayment Required ResponseJSON object in the response body. -
Clientselects one of thepaymentRequirementsreturned by the server response and creates aPayment Payloadbased on theschemeof thepaymentRequirementsthey have selected. -
Clientsends the HTTP request with theX-PAYMENTheader containing thePayment Payloadto the resource server -
Resource serververifies thePayment Payloadis valid either via local verification or by POSTing thePayment PayloadandPayment Requirementsto the/verifyendpoint of afacilitator server. -
Facilitator serverperforms verification of the object based on theschemeandnetworkof thePayment Payloadand returns aVerification Response -
If the
Verification Responseis valid, the resource server performs the work to fulfill the request. If theVerification Responseis invalid, the resource server returns a402 Payment Requiredstatus and aPayment Required ResponseJSON object in the response body. -
Resource servereither settles the payment by interacting with a blockchain directly, or by POSTing thePayment PayloadandPayment PaymentRequirementsto the/settleendpoint of afacilitator server. -
Facilitator serversubmits the payment to the blockchain based on theschemeandnetworkof thePayment Payload. -
Facilitator serverwaits for the payment to be confirmed on the blockchain. -
Facilitator serverreturns aPayment Execution Responseto the resource server. -
Resource serverreturns a200 OKresponse to theClientwith the resource they requested as the body of the HTTP response, and aX-PAYMENT-RESPONSEheader containing theSettlement Responseas Base64 encoded JSON if the payment was executed successfully.
// Payment Required Response
{
// Version of the x402 payment protocol
x402Version: int,
// List of payment requirements that the resource server accepts. A resource server may accept on multiple chains, or in multiple currencies.
accepts: [paymentRequirements]
// Message from the resource server to the client to communicate errors in processing payment
error: string
}
// paymentRequirements
{
// Scheme of the payment protocol to use
scheme: string;
// Network of the blockchain to send payment on
network: string;
// Maximum amount required to pay for the resource in atomic units of the asset
maxAmountRequired: uint256 as string;
// URL of resource to pay for
resource: string;
// Description of the resource
description: string;
// MIME type of the resource response
mimeType: string;
// Output schema of the resource response
outputSchema?: object | null;
// Address to pay value to
payTo: string;
// Maximum time in seconds for the resource server to respond
maxTimeoutSeconds: number;
// Address of the EIP-3009 compliant ERC20 contract
asset: string;
// Extra information about the payment details specific to the scheme
// For `exact` scheme on a EVM network, expects extra to contain the records `name` and `version` pertaining to asset
extra: object | null;
}
// `Payment Payload` (included as the `X-PAYMENT` header as base64 encoded json)
{
// Version of the x402 payment protocol
x402Version: number;
// scheme is the scheme value of the accepted `paymentRequirements` the client is using to pay
scheme: string;
// network is the network id of the accepted `paymentRequirements` the client is using to pay
network: string;
// payload is scheme dependent
payload: <scheme dependent>;
}
A facilitator server is a 3rd party service that can be used by a resource server to verify and settle payments, without the resource server needing to have access to a blockchain node or wallet.
// Verify a payment with a supported scheme and network
POST /verify
Request body JSON:
{
x402Version: number;
paymentHeader: string;
paymentRequirements: paymentRequirements;
}
Response:
{
isValid: boolean;
invalidReason: string | null;
}
// Settle a payment with a supported scheme and network
POST /settle
Request body JSON:
{
x402Version: number;
paymentHeader: string;
paymentRequirements: paymentRequirements;
}
Response:
{
// Whether the payment was successful
success: boolean;
// Error message from the facilitator server
error: string | null;
// Transaction hash of the settled payment
txHash: string | null;
// Network id of the blockchain the payment was settled on
networkId: string | null;
}
// Get supported payment schemes and networks
GET /supported
Response:
{
kinds: [
{
"scheme": string,
"network": string,
}
]
}
A scheme is a logical way of moving money.
Blockchains allow for a large number of flexible ways to move money. To help facilitate an expanding number of payment use cases, the x402 protocol is extensible to different ways of settling payments via its scheme field.
Each payment scheme may have different operational functionality depending on what actions are necessary to fulfill the payment.
For example exact, the first scheme shipping as part of the protocol, would have different behavior than upto. exact transfers a specific amount (ex: pay $1 to read an article) while a theoretical upto would transfer up to an amount, based on the resources consumed during a request (ex: generating tokens from an LLM).
See specs/schemes for more details on schemes, and see specs/schemes/exact/scheme_exact_evm.md to see the first proposed scheme for exact payment on EVM chains.
Because a scheme is a logical way of moving money, the way a scheme is implemented can be different for different blockchains. (ex: the way you need to implement exact on Ethereum is very different than the way you need to implement exact on Solana)
Clients and facilitator must explicitly support different (scheme, network) pairs in order to be able to create proper payloads and verify / settle payments.
-
From
examples/typescriptrunpnpm installandpnpm buildto ensure all dependent packages and examples are setup. -
Select a server, i.e. express, and cd to that example. Add your servers ethereum address to get paid to into the .env file, and then run pnpm dev in that directory.
-
Select a client, i.e. axios, and cd into that example. Add your private key for the account making payments into the .env file, and then run pnpm dev in that directory.
You should see activity across both terminals, and the client terminal will display a weather report.
- Navigate to the typescript directory:
cd typescript - Install dependencies:
pnpm install - Run the unit tests:
pnpm test
This will run the unit tests for the x402 packages.