# Overview

Fast Skill is complete payment infrastructure designed for AI agents. Its payment stack consists of three integrated layers shown below:

These docs are intentionally high-level. The implementation source of truth lives in the [Fast SDK monorepo on GitHub](https://github.com/fastxyz/fast-sdk), which contains the SDKs, shared packages, and CLI used across the Fast developer stack.

The monorepo currently includes seven core packages:

| Package                     | Role                                                       | GitHub                                                                                                         |
| --------------------------- | ---------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------- |
| `@fastxyz/sdk`              | Core Fast network SDK for signing, submission, and queries | [packages/fast-sdk](https://github.com/fastxyz/fast-sdk/blob/main/packages/fast-sdk/README.md)                 |
| `@fastxyz/allset-sdk`       | Cross-network settlement and bridging through AllSet       | [packages/allset-sdk](https://github.com/fastxyz/fast-sdk/blob/main/packages/allset-sdk/README.md)             |
| `@fastxyz/x402-client`      | Client-side support for x402-paid HTTP requests            | [packages/x402-client](https://github.com/fastxyz/fast-sdk/blob/main/packages/x402-client/README.md)           |
| `@fastxyz/x402-server`      | Server-side middleware for x402-protected routes           | [packages/x402-server](https://github.com/fastxyz/fast-sdk/blob/main/packages/x402-server/README.md)           |
| `@fastxyz/x402-facilitator` | Verification and settlement service for x402 flows         | [packages/x402-facilitator](https://github.com/fastxyz/fast-sdk/blob/main/packages/x402-facilitator/README.md) |
| `@fastxyz/fast-schema`      | Shared schemas and codecs for Fast APIs and payloads       | [packages/fast-schema](https://github.com/fastxyz/fast-sdk/blob/main/packages/fast-schema/README.md)           |
| `@fastxyz/x402-types`       | Shared protocol types and helpers for x402                 | [packages/x402-types](https://github.com/fastxyz/fast-sdk/blob/main/packages/x402-types/README.md)             |

The same monorepo also includes the [Fast CLI](https://github.com/fastxyz/fast-sdk/blob/main/app/cli/README.md), which exposes account, funding, transfer, and x402 payment workflows from the terminal.

```
                        FAST SKILL PAYMENT STACK

 +-----------------------------------+  +-------------------------------+
 |    Payment Protocol Adapters      |  |     Funding Abstraction       |
 |    Entity <-> Entity Agreement    |  |   Fiat <-> Crypto Agreement   |
 |                                   |  |                               |
 |  +-------+  +-------+  +-------+  |  |  +--------+ +-------+ +-----+ |
 |  | x402  |  |  ACP  |  |Stripe |  |  |  | Credit | |Stable-| |Bank | |
 |  +-------+  +-------+  +-------+  |  |  |  Card  | | coins | |Xfer | |
 |                                   |  |  +--------+ +-------+ +-----+ |
 +-----------------+-----------------+  +---------------+---------------+
                   |                                    |
                  API                            On/Off ramping
                   |                                    |
                   v                                    v
 +---------------------------------------------------------------------+
 |                                                                     |
 |                       Core SDK Execution                            |
 |                  Account <-> Account Agreement                      |
 |                                                                     |
 |   +---------------------+     +---------------------------+         |
 |   |      Fast SDK       |     |        AllSet SDK         |         |
 |   |   Fast <-> Fast     |     | Fast/Chain <-> Fast/Chain |         |
 |   +----------+----------+     +-------------+-------------+         |
 |              |                              |                       |
 |              v                              v                       |
 |   +-----------------------------------------------------+           |
 |   |                   FAST network                      |           |
 |   +-----------------------------------------------------+           |
 |                                                                     |
 +---------------------------------------------------------------------+

```

### Core SDK Execution

The foundation layer handles account-to-account operations on the Fast network:\
\
• Fast SDK — Native Fast-to-Fast transfers with sub-second settlement\
• AllSet SDK — Seamless movement between Fast and external networks (Base, Arbitrum, Ethereum, etc.) without bridging complexity

### Payment Protocol Adapters

Entity-to-entity payment protocols that standardize how agents request and send payments:\
\
• x402 — HTTP-native payment protocol (pay-per-API-call)\
• ACP — Agent Communication Protocol for agent-to-agent commerce\
• Stripe — Traditional payment rails integration

### Funding Abstraction

Simplifies how money enters and exits the system:\
\
• Credit card on-ramps\
• Stablecoin deposits\
• Bank transfers

The SDK exposes these layers through three composable primitives — `FastProvider`, `Signer`, and `TransactionBuilder` — that handle serialization, signing, and network communication automatically. For installation details, runnable examples, and package-level APIs, see the [Fast SDK monorepo on GitHub](https://github.com/fastxyz/fast-sdk).


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