> For the complete documentation index, see [llms.txt](https://x402.gitbook.io/x402/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://x402.gitbook.io/x402/core-concepts.md).

# core-concepts

- [Client / Server](https://x402.gitbook.io/x402/core-concepts/client-server.md): This page explains the roles and responsibilities of the \*\*client\*\* and \*\*server\*\* in the x402 protocol.
- [Facilitator](https://x402.gitbook.io/x402/core-concepts/facilitator.md): This page explains the role of the \*\*facilitator\*\* in the x402 protocol.
- [HTTP 402](https://x402.gitbook.io/x402/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
- [Wallet](https://x402.gitbook.io/x402/core-concepts/wallet.md): This page explains the role of the \*\*wallet\*\* in the x402 protocol.