> ## Documentation Index
> Fetch the complete documentation index at: https://docs.x0protocol.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# x0 Protocol

> Autonomous agent payment infrastructure on Solana — policy-enforced transfers, conditional escrow, on-chain reputation, and zero-knowledge proof verification.

## What is x0?

x0 is a suite of **eight interoperating Solana programs** and a **TypeScript SDK** that enables autonomous AI agents to transact with programmable guardrails. Every transfer is policy-enforced at the Token-2022 level via transfer hooks, ensuring agents can never exceed their configured spend limits — even if their signing keys are compromised.

The protocol employs the **HTTP 402 Payment Required** flow for machine-to-machine commerce: an agent discovers a service, negotiates price on-chain, pays via policy-gated transfer, and receives a cryptographic receipt — all without human intervention.

<Columns cols={3}>
  <Card title="Protocol Specifications" icon="book" href="/protocol/architecture">
    Deep technical reference for all eight on-chain programs, state accounts, instructions, and cryptographic primitives.
  </Card>

  <Card title="SDK for Developers" icon="code" href="/sdk/installation">
    TypeScript SDK with instruction builders, PDA derivation, Blink generation, x402 helpers, and confidential transfer support.
  </Card>

  <Card title="Security Analysis" icon="shield" href="/security/threat-model">
    Threat model, attack vector mitigations, formal invariants, and audit status.
  </Card>
</Columns>

***

## Architecture at a Glance

The protocol consists of three layers:

<Steps>
  <Step title="Policy Enforcement Layer">
    **x0-guard** acts as a Token-2022 transfer hook. Every token transfer is intercepted and validated against the agent's `AgentPolicy` — checking daily spend limits, rolling window budgets, whitelist membership, and privacy mode. Transfers that violate policy are rejected at the Solana runtime level.
  </Step>

  <Step title="Service Layer">
    **x0-escrow**, **x0-registry**, **x0-reputation**, and **x0-wrapper** provide the transactional infrastructure: conditional escrow with dispute resolution, agent discovery with capability metadata, on-chain reputation scoring, and a 1:1 USDC-backed stablecoin wrapper (x0-USD) with timelocked governance.
  </Step>

  <Step title="Cryptographic Layer">
    **x0-token**, **x0-zk-verifier**, and the off-chain **x0-zk-proofs** WASM library handle Token-2022 mint management, confidential transfers via Twisted ElGamal encryption, and on-chain Groth16 proof verification for balance privacy.
  </Step>
</Steps>

***

## Program Map

| Program        | Address                                        | Purpose                                                     |
| -------------- | ---------------------------------------------- | ----------------------------------------------------------- |
| x0-guard       | `2uYGW3fQUGfhrwVbkupdasXBpRPfGYBGTLUdaPTXU9vP` | Policy enforcement via transfer hook                        |
| x0-token       | `EHHTCSyGkmnsBhGsvCmLzKgcSxtsN31ScrfiwcCbjHci` | Token-2022 mint with transfer fees + confidential transfers |
| x0-escrow      | `AhaDyVm8LBxpUwFdArA37LnHvNx6cNWe3KAiy8zGqhHF` | Conditional escrow with dispute resolution                  |
| x0-registry    | `Bebty49EPhFoANKDw7TqLQ2bX61ackNav5iNkj36eVJo` | Agent discovery and capability registry                     |
| x0-reputation  | `FfzkTWRGAJQPDePbujZdEhKHqC1UpqvDrpv4TEiWpx6y` | On-chain reputation oracle                                  |
| x0-wrapper     | `EomiXBbg94Smu4ipDoJtuguazcd1KjLFDFJt2fCabvJ8` | USDC → x0-USD 1:1 wrapper with governance                   |
| x0-zk-verifier | `zQWSrznKgcK8aHA4ry7xbSCdP36FqgUHj766YM3pwre`  | On-chain zero-knowledge proof verification                  |
| x0-common      | *(library)*                                    | Shared constants, errors, events, state types               |

<Card title="Read the Whitepaper" icon="file-lines" href="https://raw.githubusercontent.com/0xTnxl/x0/main/whitepaper.pdf">
  Full formal specification with mathematical proofs, security analysis, and protocol economics.
</Card>