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https://github.com/coinbase/x402

A payments protocol for the internet. Built on HTTP.
https://github.com/coinbase/x402

Last synced: 14 days ago
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A payments protocol for the internet. Built on HTTP.

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README 

        
# x402 payments protocol



> "1 line of code to accept digital dollars. No fee, 2 second settlement, $0.001 minimum payment."



```typescript

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.

```



## Philosophy



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.



## Principals



- **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](https://github.com/coinbase/x402/blob/main/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](https://github.com/coinbase/x402/blob/main/ROADMAP.md)



## Terms:



- `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.



## Technical Goals:



- 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



## V1 Protocol



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:



1. A schema for how servers can respond to clients to facilitate payment for a resource (`PaymentRequirements`)

2. A standard header `X-PAYMENT` that is set by clients paying for resources

3. A standard schema and encoding method for data in the `X-PAYMENT` header

4. A recommended flow for how payments should be verified and settled by a resource server

5. A REST specification for how a resource server can perform verification and settlement against a remote 3rd party server (`facilitator`)

6. A specification for a `X-PAYMENT-RESPONSE` header that can be used by resource servers to communicate blockchain transactions details to the client in their HTTP response



### V1 Protocol Sequencing



![](./static/x402-protocol-flow.png)



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.



1. `Client` makes an HTTP request to a `resource server`



2. `Resource server` responds with a `402 Payment Required` status and a `Payment Required Response` JSON object in the response body.



3. `Client` selects one of the `paymentRequirements` returned by the server response and creates a `Payment Payload` based on the `scheme` of the `paymentRequirements` they have selected.



4. `Client` sends the HTTP request with the `X-PAYMENT` header containing the `Payment Payload` to the resource server



5. `Resource server` verifies the `Payment Payload` is valid either via local verification or by POSTing the `Payment Payload` and `Payment Requirements` to the `/verify` endpoint of a `facilitator server`.



6. `Facilitator server` performs verification of the object based on the `scheme` and `network` of the `Payment Payload` and returns a `Verification Response`



7. If the `Verification Response` is valid, the resource server performs the work to fulfill the request. If the `Verification Response` is invalid, the resource server returns a `402 Payment Required` status and a `Payment Required Response` JSON object in the response body.



8. `Resource server` either settles the payment by interacting with a blockchain directly, or by POSTing the `Payment Payload` and `Payment PaymentRequirements` to the `/settle` endpoint of a `facilitator server`.



9. `Facilitator server` submits the payment to the blockchain based on the `scheme` and `network` of the `Payment Payload`.



10. `Facilitator server` waits for the payment to be confirmed on the blockchain.



11. `Facilitator server` returns a `Payment Execution Response` to the resource server.



12. `Resource server` returns a `200 OK` response to the `Client` with the resource they requested as the body of the HTTP response, and a `X-PAYMENT-RESPONSE` header containing the `Settlement Response` as Base64 encoded JSON if the payment was executed successfully.



### Type Specifications



#### Data types



```

// 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: ;

}

```



#### Facilitator Types & Interface



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,

    }

  ]

}



```



### Schemes



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.



### Schemes vs Networks



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.



## Running example



1. From `examples/typescript` run `pnpm install` and `pnpm build` to ensure all dependent packages and examples are setup.



2. 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.



3. 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.



## Running tests



1. Navigate to the typescript directory: `cd typescript`

2. Install dependencies: `pnpm install`

3. Run the unit tests: `pnpm test`



This will run the unit tests for the x402 packages.