# x402

- [Welcome to x402](https://docs.x402.org/introduction.md): This guide will help you understand x402, the open payment standard, and help you get started building or integrating services with x402.
- [FAQ](https://docs.x402.org/faq.md)
- [Quickstart for Buyers](https://docs.x402.org/getting-started/quickstart-for-buyers.md): This guide walks you through how to use **x402** to interact with services that require payment. By the end of this guide, you will be able to programmatically discover payment requirements, complete a payment, and access a paid resource.
- [Quickstart for Sellers](https://docs.x402.org/getting-started/quickstart-for-sellers.md): This guide walks you through integrating with **x402** to enable payments for your API or service. By the end, your API will be able to charge buyers and AI agents for access.
- [HTTP 402](https://docs.x402.org/core-concepts/http-402.md): For decades, HTTP 402 Payment Required has been reserved for future use. x402 unlocks it, and [absolves the internet of its original sin](https://economyofbits.substack.com/p/marc-andreessens-original-sin).
- [Client / Server](https://docs.x402.org/core-concepts/client-server.md): This page explains the roles and responsibilities of the **client** and **server** in the x402 protocol.
- [Facilitator](https://docs.x402.org/core-concepts/facilitator.md): This page explains the role of the **facilitator** in the x402 protocol.
- [Wallet](https://docs.x402.org/core-concepts/wallet.md): This page explains the role of the **wallet** in the x402 protocol.
- [Networks & Token Support](https://docs.x402.org/core-concepts/network-and-token-support.md): This page explains which blockchain networks and tokens are supported by x402, and how to extend support to additional networks.
- [Payment Schemes](https://docs.x402.org/schemes/overview.md): Choose between exact, upto, and batch-settlement payment schemes in x402.
- [Exact](https://docs.x402.org/schemes/exact.md): Fixed-price x402 payments where the buyer authorizes exactly the advertised amount.
- [Upto](https://docs.x402.org/schemes/upto.md): Usage-based x402 payments where the buyer authorizes a maximum and the seller charges actual usage.
- [Batch Settlement](https://docs.x402.org/schemes/batch-settlement.md): High-throughput EVM payments with escrow, off-chain vouchers, and batched onchain redemption.
- [Extensions Overview](https://docs.x402.org/extensions/overview.md): x402 extensions are composable, optional capabilities that plug into the payment lifecycle. They enrich 402 responses, settlement responses, or both — without changing your business logic.
- [Bazaar (Discovery Layer)](https://docs.x402.org/extensions/bazaar.md): The x402 Bazaar is the discovery layer for the x402 ecosystem - a machine-readable catalog that helps developers and AI agents find and integrate with x402-compatible API endpoints and MCP tools.
- [Builder Code (ERC-8021)](https://docs.x402.org/extensions/builder-code.md): The builder-code extension enables on-chain attribution tracking for x402 payments by appending ERC-8021 Schema 2 builder codes to settlement transaction calldata.
- [Payment-Identifier (Idempotency)](https://docs.x402.org/extensions/payment-identifier.md): The payment-identifier extension enables idempotency for x402 payments, allowing clients to safely retry requests without duplicate payment processing.
- [Sign-In-With-X (SIWX)](https://docs.x402.org/extensions/sign-in-with-x.md): CAIP-122 wallet authentication for x402-protected resources. Prove wallet ownership to access previously purchased content without repaying.
- [Signed Offers & Receipts](https://docs.x402.org/extensions/offer-receipt.md): Sign offers on 402 responses and receipts on 200 responses, producing cryptographic proof-of-interaction artifacts that clients can use for reputation, auditing, or dispute resolution.
- [EIP-2612 Gas Sponsoring](https://docs.x402.org/extensions/eip2612-gas-sponsoring.md): Gasless Permit2 approval for ERC-20 tokens that implement EIP-2612. The facilitator submits the permit onchain, so the client never pays gas for the approval step.
- [ERC-20 Approval Gas Sponsoring](https://docs.x402.org/extensions/erc20-approval-gas-sponsoring.md): Gasless Permit2 approval for any ERC-20 token, including those without EIP-2612. The facilitator sponsors the gas for the approval transaction.
- [Lifecycle Hooks](https://docs.x402.org/advanced-concepts/lifecycle-hooks.md): This page explains how to use lifecycle hooks to customize x402 payment flows.
- [Wallet Compatibility](https://docs.x402.org/advanced-concepts/wallet-compatibility.md): Which wallet types work with which x402 schemes, and why, based on how signatures are verified on-chain.
- [MCP Server with x402](https://docs.x402.org/guides/mcp-server-with-x402.md): [Model Context Protocol (MCP)](https://modelcontextprotocol.io/) is a protocol for passing context between LLMs and other AI agents. This page shows how to use the x402 payment protocol with MCP to make paid API requests through an MCP server, and how to connect it to Claude Desktop.
- [Migration Guide: V1 to V2](https://docs.x402.org/guides/migration-v1-to-v2.md): This guide helps you migrate from x402 V1 to V2. The V2 protocol introduces standardized identifiers, improved type safety, and a more modular architecture.
- [Developer Tools](https://docs.x402.org/dev-tools/overview.md): Community-built x402 packages and tools.
- [Third-Party SDKs](https://docs.x402.org/dev-tools/third-party-sdks.md): Community-maintained x402 SDKs.
- [Third-Party Extensions](https://docs.x402.org/dev-tools/third-party-extensions.md): Packages built by ecosystem partners that extend x402 beyond the core specification.
- [Facilitators](https://docs.x402.org/dev-tools/facilitators.md): Production facilitator services for x402 payments.
- [SDK Features](https://docs.x402.org/sdk-features.md): Feature parity across TypeScript, Go, and Python SDKs

## Optional

- [x402.org](https://x402.org)
- [GitHub](https://github.com/x402-foundation/x402)
- [Slack](http://slack.x402.org/)
- [Vercel Starter](https://vercel.com/templates/ai/x402-ai-starter)